US20090306302A1

US20090306302A1 - Process of free-radical polymerization in aqueous disperasion for the preparation of polymers

Info

Publication number: US20090306302A1
Application number: US12/308,977
Authority: US
Inventors: Patrick Lacroix-Desmazes; Jeff Tonnar
Original assignee: CID CENTRO DE INVESTIGACION Y DESARROLLO TECNOLOGICO SADECV
Current assignee: Macro M SA de CV
Priority date: 2006-07-04
Filing date: 2007-07-04
Publication date: 2009-12-10
Also published as: EP2041185B1; US8541524B2; FR2903409A1; JP5201419B2; WO2008003729A3; MX2008016485A; JP2009541567A; EP2041185A1; EP2049573A2; WO2008003728A1; US20090292071A1; WO2008003729A2

Abstract

Process of free-radical polymerization in aqueous dispersion for the preparation of polymers, employing (A) at least one ethylenically unsaturated monomer, one of which is employed as the principal monomer and is selected from styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers, (B) at least one free-radical initiator selected from diazo compounds, peroxides and dialkyldiphenylalkanes, (C) molecular iodine, and (D) at least one oxidizing agent whose solubility in water is at least 10 g/l, of which at least one may be the one (B); said process comprising the steps whereby (1) at least one fraction of each of compounds (A), (B), (C) and (D) is introduced into a reactor, and (2) the contents of the reactor are reacted while introducing into the reactor the remainder, where appropriate, of each of compounds (A), (B), (C) and (D). Process of free-radical polymerization in aqueous dispersion for the preparation of block copolymers starting from polymers prepared by the abovementioned process.

Description

The present application claims the benefit of the provisional U.S. application Ser. No. 60/818276 filed on Jul. 5, 2006.
The present invention relates to a process of free-radical polymerization in aqueous dispersion for the preparation of polymers and a process of free-radical polymerization in aqueous dispersion for the preparation of block copolymers.
Although free-radical polymerization is the mechanism of chain polymerization that is capable of accepting the least stringent experimental conditions and the widest range of monomers, providing it with the characteristics of a living polymerization has presented a major challenge for a long time. The main limitation of conventional free-radical polymerization originates in the decisive significance of the irreversible termination reactions via combination and/or dismutation of the free radicals assuring the growth of the chains.
The growing chains are initiated, they grow, and are then terminated in a random, irreversible manner, in parallel with the initiation of new chains. The polymerization stops when all of the polymer chains, whose lengths are variable and non-predictable, are inactive. This technique thus offers only few possibilities of influencing molecular weight, molecular weight distribution, the nature of the chain ends, and, more generally, the molecular structure of the polymer.
In recent years there have been significant and successful attempts to develop novel free-radical polymerization techniques permitting the minimization of the relative significance of irreversible termination reactions in comparison with initiation and propagation reactions. These techniques are known as controlled free-radical polymerization. The characteristic that these novel techniques have in common is the employment of a control agent (X) which brings about transient conversion of the free radical of the growing chain to a dormant species (P-X), i.e., in equilibrium with the active species (P).
Among the best known methods, mention may be made of free-radical polymerization controlled by nitroxides (nitroxide mediated polymerization or NMP), atom transfer (atom transfer radical polymerization or ATRP), chain transfer (reversible addition-fragmentation chain transfer polymerization (RAFT/MADIX), and iodine transfer (iodine transfer polymerization or ITP), which employ nitroxide radicals, halogens activated in the presence of metallic complexes, dithiocarbonyl compounds, and organic iodide molecules, respectively, as control agents.
Although these methods have been successfully studied for the case of polymerization in solution and in bulk, few studies have dealt with polymerization in aqueous dispersion, which is widely employed in industry.
More recently, the reverse iodine transfer polymerization (RITP) technique, which employs iodine as a control agent, has been developed. For example, patent application WO 03/097704 discloses such a process of mediated free-radical polymerization, wherein at least one ethylenically unsaturated monomer is polymerized in the presence of at least one free-radical initiator (free-radical generator) and molecular iodine.
In the particular case of RITP, wherein an iodine molecule controls two polymerization chains, the intended molecular weight (M_n) of the polymer, for 100% conversion, is controlled by the ratio between the weight of monomer and twice the number of initial moles of iodine (n_{I2, initial}), according to equation 1 below, wherein M_A-Iis the molecular weight of the chain ends:
M _n=(weight of monomer)/(2×n_{I2, initial})+M _A-I (equation 1)
Although the text of the application WO 03/097704 describes the polymerization of vinyl chloride in aqueous suspension, the process concerned does not, however, provide a polymer of which the experimental average molecular weight (20,000) closely approximates the theoretical average molecular weight (intended molecular weight, taking into account the degree of conversion) (8700).
Thus there is still a need to develop a process of controlled free-radical polymerization in aqueous dispersion, wherein the control agent is such that the intended theoretical average molecular weight closely approximates the molecular weight actually measured after polymerization.
An object of the present invention is therefore to provide a process of free-radical polymerization in aqueous dispersion for the preparation of polymers that permits better control of the polymerization and therefore the average molecular weight of the polymers obtained compared with the processes of the prior art, while retaining their advantages.
The invention therefore relates to a process of free-radical polymerization in aqueous suspension for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer, one of which is employed as the principal monomer and is selected from styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one free-radical initiator selected among diazo compounds, peroxides and dialkyldiphenylalkanes,
(C) molecular iodine, and
(D) at least one oxidizing agent whose solubility in water is at least 10 g/l, of which at least one may be one of (B); said process comprising the steps whereby
(1) at least one fraction of each of the compounds (A), (B), (C) and (D) is introduced into a reactor, and
(2) the contents of the reactor are reacted while introducing into the reactor any remainder of each of the compounds (A), (B), (C) and (D).
By polymerization in aqueous dispersion, it is intended to denote processes of polymerization taking place in water in the presence of at least one surfactant.
The expression at least one surfactant means that the process of ploymerization may take place in the presence of one or more surfactants.
By surfactant, it is intended to denote any compound having in its structure one or more hydrophilic components and one or more hydrophobic components. This hydrophilic/hydrophobic interplay enables the surfactant to have an interfacial activity, which in turn ensures dispersion and stabilization of the aqueous and organic phases.
Certain polymerizations in aqueous dispersion may also be achieved with exclusion of surfactant(s), but as a consequence, with the formation of unstable aqueous dispersions characterized by a very low solid content. The present invention does not relate to such polymerizations but instead to polymerizations in aqueous dispersion achieved in the presence of at least one surfactant.
Among the surfactants, mention may be made of dispersing agents, also known as protective colloids or suspension agents (henceforth known as dispersers), as well as emulsifiers.
By polymerization in aqueous dispersion, it is intended to denote free-radical polymerization in aqueous suspension, free-radical polymerization in aqueous microsuspension, free-radical polymerization in aqueous emulsion, and free-radical polymerization in aqueous mini-emulsion.
By free-radical polymerization in aqueous suspension, it is intended to denote any process of free-radical polymerization taking place in aqueous medium in the presence of dispersers as surfactants and oil-soluble free-radical initiators.
By polymerization in aqueous microsuspension, also known as polymerization in homogenized aqueous dispersion, it is intended to denote any process of free-radical polymerization in which oil-soluble radical generators are employed and in which a monomer droplet emulsion is obtained by high power mechanical stirring and which is characterized by having emulsifiers as surfactants.
By free-radical polymerization in aqueous emulsion, it is intended to denote any process of free-radical polymerization taking place in aqueous medium in the presence of emulsifiers as surfactants and water-soluble radical generators. Free-radical polymerization in aqueous emulsion is sometimes also known as polymerization in ab initio emulsion.
By polymerization in aqueous mini-emulsion, it is intended to denote any process of free-radical polymerization in which oil-soluble radical generators and/or water-soluble radical generators as well as a hydrophobe are employed and a monomer droplet emulsion is obtained by high power mechanical stirring and which is characterized by having emulsifiers and, where appropriate, dispersers as surfactants.
As examples of dispersers, mention may be made of partially hydrolized polyvinylacetates, gelatin, starch, polyvinylpyrrolidinone, vinyl acetate and maleic anhydride copolymers, derivatives of water soluble cellolose ethers such as methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxypropyl methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose.
As dispersers, preference is given to derivatives of water-soluble cellulose ethers. Among the latter, particular preference is given to hydroxypropyl methylcellulose.
Emulsifiers can be anionic emulsifiers, nonionic emulsifiers, or cationic emulsifiers.
Among the anionic emulsifiers, non-limiting mention may made of alkyl sulfates such as sodium laurylsulfate, alkyl sulfonates such as sodium dodecylbenzene sulfonate and sodium 1-hexadecanesulphonate in pure form or in a mixture of C₁₂-C₂₀alkyl sulfonates, sometimes known as paraffin sulfonates, alkylaryl mono- or disulfonates, and dialkyl sulfosuccinates such as sodium diethylhexylsulfosuccinate and sodium dihexylsulfosuccinate.
Among the nonionic emulsifiers, non-limiting mention may be made of alkyl or alkylaryl ethoxylated derivatives, alkyl or alkylaryl propoxylated derivatives, and sugar esters or sugar ethers.
Among the cationic emulsifiers, non-limiting mention may be made of ethoxylated and propoxylated alkylamines.
Preference is given to anionic emulsifiers as emulsifiers, where appropriate in mixtures with one or more nonionic emulsifiers. Particular preference is given to anionic emulsifiers.
Hydrophobes can be alkanes such as hexadecane, silanes, siloxanes, perfluorinated alkanes, or compounds standardly employed as pigments, comonomers, transfer agents, generators, or plasticizers, as long as they are hydrophobes.
The process of the invention for the preparation of polymers employs at least one ethylenically unsaturated monomer, one of which is employed as a principal monomer and is selected from styrene and its derives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers.
The expression at least one ethylenically unsaturated monomer, one of which is employed as a principal monomer, means that the process of polymerization may employ one or more ethylenically unsaturated monomers and that in the case where several monomers are employed, one of them is employed as a principal monomer.
By principal monomer, it is intended to denote the monomer comprising at least 100/n/% by weight of the monomer mixture and which will generate at least 100/n/% by weight of the monomer units of the ploymer obtained, n being the number of monomers in the monomer mixture.
The ethylenically unsaturated monomer employed as a principal monomer is selected among styrene and its derives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers.
Among the styrene derivatives, mention may be made of para-tert-butylstyrene, para-methylstyrene, meta-methylstyrene, alpha-methylstyrene, para-bromostyrene, para-chlorostyrene, meta-(1-chloroethyl) styrene, para-fluorostyrene, para-trifluoromethylstyrene, meta-trifluoromethylstyrene, pentafluorostyrene, para-acetoxystyrene, para-methoxystyrene, para-tert-butoxystyrene, para-epoxystyrene, para-aminostyrene, the alkali metal salts of styrene-para-sulfonic acid, vinylbenzoic acid, para-chloromethylstyrene, perfluorooctyl-ethyleneoxy-methylstyrene, N,N-dimethyl-vinyl-benzylamine, vinyl-benzyl-trimethyl ammonium chloride, and 3-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate. Particular preference is given to styrene.
By acrylic acid derivatives, it is intended to denote acrylic acid salts such as alkali metal salts, acrylic acid protected by a trimethylsilyl, tert-butyl, tetrahydropyranyl, 1-ethoxyethyl, or benzyl group, alkyl acrylates, acrylonitrile, acrylamide and its derivatives.
Among the alkyl acrylates, mention may be made of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, s-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, stearyl acrylate, glycidyl acrylate, benzyl acrylate, isobornyl acrylate, lauryl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, 2-dimethylaminoethyl acrylate, 2-trimethylaminoethyl acrylate chloride, the potassium salt of 3-sulfopropyl acrylate, the fluoroalkyl acrylates such as 1,1,2,2-tetrahydroperfluorodecyl acrylate, allyl acrylate, vinyl acrylate, protected or unprotected sugars and nucleotides such as 2-beta-D-glucopyranosyloxyethyl acrylate, n-butyl alpha-fluoro acrylate, 2-(2-bromopropionyloxy)ethyl acrylate, 2-(2-bromoisobutyryloxy) ethyl acrylate, carboxyethylacrylate, tetrahydropyranyl acrylate, 1-ethoxyethyl acrylate, and acrylate macromonomers such as poly(ethylene oxide) acrylate and poly(dimethylsiloxane) acrylate. Particular preference is given to butyl acrylate and 2-ethylhexyl acrylate.
Among the acrylamide derivatives, mention may be made of N,N-dimethylacrylamide, tert-butylacrylamide, N-hydroxymethylacrylamide, N-acetamidoacrylamide, N-methylolacrylamide, N-methylolacrylamide methyl ether, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) or one of its salts, such as the sodium salt, the sodium salt of 3-acrylamido-3-methylbutanoate, and N-isopropylacrylamide.
By methacrylic acid derivatives, it is intended to denote methacrylic acid salts such as alkali metal salts, methacrylic acid protected by a trimethylsilyl, tert-butyl, tetrahydropyranyl, 1-ethoxyethyl, or benzyl group, alkyl methacrylates, methacrylonitrile, and methacrylamide and its derivatives.
Among the alkyl methacrylates, mention may be made of methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, s-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, glycidyl methacrylate, benzyl methacrylate, isobornyl methacrylate, bornyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, fluoroalkyl methacrylates such as 1,1,2,2-tetrahydroperfluorodecyl methacrylate, allyl methacrylate, vinyl methacrylate, tetrahydropyranyl methacrylate, 2-(N-morpholino)ethyl methacrylate, 2-(dimethylamino)ethyl methacrylate, 2-trimethylaminoethyl methacrylate chloride, 2-aminoethyl methacrylate, dimethylaminopropyl methacrylate, 2-sulfoethyl methacrylate, the potassium salt of 3-sulfopropyl methacrylate, protected or unprotected sugars and nucleotides such as 5′-methacrylouridine, 2-(2-bromopropionyloxy)ethyl methacrylate, 2-(2-bromoisobutyryloxy)ethyl methacrylate, N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropylammonium betame), acetoacetoxyethyl methacrylate, carboxyethyl methacrylate, 1-ethoxyethyl methacrylate, and methacrylate macromonomers such as poly(ethylene oxide) methacrylate and poly(dimethylsiloxane) methacrylate. Particular preference is given to methyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate.
Among the methacrylamide derivatives, mention may be made of N,N-(2-hydroxypropyl)methacrylamide, [3-(methacryloylamino)propyl]trimethyl ammonium chloride, methacryloyl aminopropyl dimethyl ammonium sulfobetaine.
Among the diene monomers, mention may be made of butadiene, isoprene, chloroprene, and isobutene. Particular preference is given to butadiene and chloroprene.
Among the vinyl esters, mention may be made of vinyl acetate, vinyl trifluoroacetate, vinyl versatate, tert-decanoic acid ethylene ester (VeoVa10), neononanoic acid ethylene ester (VeoVa9), and vinyl pivalate. Particular preference is given to vinyl acetate.
Among the vinyl ethers, mention may be made of methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isobutyl vinyl ether, n-butyl vinyl ether, cyclohexyl vinyl ether, 2-methoxyethyl vinyl ether, 2-chloroethyl vinyl ether, 2-chloroethyl propenyl ether, 3-bromo-n-propyl vinyl ether, 4-chloro-n-butyl vinyl ether, 2-hydroxy ethyl vinyl ether, 4-hydroxy butyl vinyl ether, 6-hydroxyhexyl vinyl ether, 4-hydroxymethyl cyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether, diethylene glycol monovinyl ether, n-butyldiethoxy vinyl ether, n-hexylethoxy vinyl ether, methyl dipropylene glycol vinyl ether, cyclohexanediethanol monovinyl ether, and 2-ethylhexylethoxy vinyl ether.
Among the vinylic pyridine derivatives, mention may be made of 4-vinyl pyridine, 3-vinyl pyridine, 2-vinyl pyridine, and 1-(3-sulfopropyl)-2-vinylpyridinium betaine.
Among the vinyl sulfonic acid and vinyl phosphonic acid derivatives, mention may be made of their salts and their esters.
Among the N-vinyl monomers, mention may be made of N-vinylcarbazole, N-vinylcarbamate, N-vinylcaprolactam, N-vinylpyrrolidinone, and N-vinylimidazole.
The process of the invention is therefore advantageously a process of free-radical polymerization in aqueous dispersion for the preparation of polymers of styrene and its derivatives, of acrylic acid and its derivatives, of methacrylic acid and its derivatives, of dienes, of vinyl esters, of vinylic pyridine derivatives, of vinylsulfonic acid and its derivatives, of vinylphosphonic acid and its derivatives, and of N-vinyl monomers.
By polymers, it is intended to denote the homopolymers and the copolymers of these monomers as principal monomer. By copolymers, it is intended to denote the copolymers of one of the aforementioned monomers, which is the principal monomer, with one or more monomers copolymerizable therewith. Among the copolymerizable monomers, non-limiting mention may made of the monomers listed above as principal monomer but also maleimide-, maleate-, fumarate-, and allyl-type monomers as well as itaconic acid, crotonic acid, and maleic anhydride.
Preference is given to the process of the invention being a process of free-radical polymerization in aqueous dispersion for the preparation of polymers of styrene and its derivatives, of acrylic acid and its derivatives, of methacrylic acid and its derivatives, of dienes, of vinyl esters, and of vinyl ethers.
Particular preference is given to the process of the invention being a process of free-radical polymerization in aqueous dispersion for the preparation of polymers of styrene and its derivatives, of acrylic acid and its derivatives, and of methacrylic acid and its derivatives.
The manner of introducing the ethylenically unsaturated monomer(s) (A) in the process of the invention may be variable.
For example, in the case where (A) consists of a single ethylenically unsaturated monomer, the entirety of the monomer can be introduced in step (1) or a fraction thereof can be introduced in step (1) and the remainder in step (2). Preference is given to the introduction in step (2) being continuous.
In the case where (A) consists of at least two ethylenically unsaturated monomers, a portion of the monomers can be introduced in step (1) and the remaining portion in step (2), preferably in a continuous manner.
In the particular case where (A) consists of a mixture of at least two ethylenically unsaturated monomers, the entirety of the mixture can be introduced in step (1) or a fraction of the mixture can be introduced in step (1) and the remainder of the same mixture introduced in step (2), preferably in a continuous manner.
The process for the preparation of polymers of the invention employs at least one free-radical initiator selected among diazo compounds, peroxides, and dialkyldiphenyl alkanes.
The expression at least one free-radical initiator selected among diazo compounds, peroxides, and dialkyldiphenyl alkanes means that the process of polymerization may employ one or more free-radical initiators selected among diazo compounds, peroxides, and dialkyldiphenyl alkanes.
In the text that follows, the expression “free-radical initiator” used in the singular or the plural is to be understood as denoting one or several free-radical initiators, unless otherwise denoted.
Preference is given to the process of the invention employing at least one free-radical initiator selected among the diazo compounds and the peroxides.
Particular preference is given to the process of the invention employing a single free-radical initiator.
The free-radical initiators can be oil-soluble or water-soluble.
By oil-soluble free-radical initiators, it is intended to denote free-radical initiators that are soluble in the monomers, as used for polymerization in aqueous suspension, in microsuspension, or in aqueous mini-emulsion.
By water-soluble free-radical initiators, it is intended to denote free-radical initiators that are soluble in water, as used for polymerization in aqueous emulsion or in mini-emulsion.
The water-soluble free-radical initiator can be an oxidant as defined hereinafter.
Mention may be made of the following as examples of oil-soluble diazo compounds

- 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),
- 2,2′-azobis(2,4-dimethylvaleronitrile),
(1-phenylethyl)azodiphenyl methane,
- 2,2′-azobisisobutyronitrile,
- 1,1′-azobis(1-cyclohexanecarbonitrile),
- 2,2′-azobis(2-methylbutyronitrile),
- 2,2′-azobis(2,4,4-trimethyl pentane),
- 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, and
2,2′-azobis(2-methyl-propane).

Mention may be made of the following as examples of water-soluble diazo compounds

- 2-(carbamoylazo)-isobutyronitrile,
- 4,4′-azobis(4-cyanovaleric) acid,
- ammonium 4,4′-azobis(4-cyanovalerate),
sodium 4,4′-azobis(4-cyanovalerate),
- potassium 4,4′-azobis(4-cyanovalerate),
- 2,2′-azobis (N, N′-dimethyleneisobutyramidine),
- 2,2′-azobis(N, N′-dimethyleneisobutyramidine) dichloride,
- 2,2′-azobis(2-amidinopropane) dihydrochloride,
- 2,2′-azobis[2-methyl-N-(1,1-bis(hydroxymethyl)-2-hydroxyethyl) propionamide],
- 2,2′-azobis[2-methyl-N-(1,1-bis(hydroxymethyl)ethyl) propionamide],
- 2,2′-azobis[2-methyl-N-(2-hydroxyethyl) propionamide], and
- 2,2′-azobis(isobutyramide) dihydrate.

Preference is given to 4,4′-azobis(4-cyanovalerate), ammonium 4,4′-azobis(4-cyanovalerate), sodium 4,4′-azobis(4-cyanovalerate), and potassium 4,4′-azobis(4-cyanovalerate).
As examples of oil-soluble peroxides, mention may be made of

- diacyl peroxides such as dilauroyl peroxide, dibenzoyl peroxide, didecanoyl peroxide,
- succinoyl peroxide,
- organic hydroperoxides such as cumyl hydroperoxide and tert-amyl hydroperoxide,
- dialkyl peroxydicarbonates such as diisopropyl peroxydicarbonate, dimyristyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di[2-ethylhexyl]peroxydicarbonate, di[4-tert-butyl]cyclohexyl peroxydicarbonate, and dicetyl peroxydicarbonate,
- peresters such as t-amylperpivalate, t-butylperpivalate, t-amylperoxyneodecanoate, t-butylperoxyneodecanoate, and cumylperoxyneodecanoate.

As examples of water-soluble peroxides, mention may be made of

- inorganic peroxides such as sodium, potassium, and ammonium persulfate,
- tert-butyl hydroperoxide,
hydrogen peroxide, and
- the perborates.

Preference is given to sodium, potassium, and ammonium persulfate as well as to hydrogen peroxide.
The manner of introducing the free-radical initiators (B) into the process of the invention may be variable.
For example, in the case where (B) consists of a single free-radical initiator, the entirety of the free-radical initiator can be introduced in step (1) or a fraction thereof can be introduced in step (1) and the remainder in step (2). Preference is given to the introduction in step (2) being continuous.
In the case where (B) consists of at least two free-radical initiators, a portion of the free-radical initiators can be introduced in step (1) and the other portion in step (2), preferably in a continuous manner.
In the particular case where (B) consists of a mixture of at least to radical generators, the entirety of the mixture can be introduced in step (1) or a fraction of the mixture can be introduced in step (1) and the remainder of the same mixture in step (2), preferably in a continuous manner.
The method of the invention employs (C) molecular iodine. Molecular iodine can be employed as such or in the form of one of its a precursors.
A precursor is to be understood as a compound capable of forming molecular iodine in the polymerization medium. As examples of such precursors, mention may be made of alkali metal iodides, such as sodium iodide or potassium iodide. The conversion of the precursor into iodine can be brought about by addition of an oxidant (D′) to the polymerization medium. The oxidant (D′) capable of being employed for this purpose complies with the definition of an oxidant (D) detailed hereinafter.
The number of moles of molecular iodine (C) based on the number of moles of (A) is advantageously at least 2.5×10⁻⁵, preferably at least 5×10⁻⁵, and particularly preferably at least 10⁻⁴. Furthermore, the number of moles of molecular iodine (C) based on the number of moles of (A) is advantageously at most 10⁻¹and preferably at most 10⁻².
The molar proportion of the molecular iodine (C) or its precursor and of the oxidant (D′) introduced in the reactor in step (1) is advantageously at least 50%.
Preference is given to 100% of the molecular iodine (C) or its precursor and the oxidant (D′) being introduced in the reactor in step (1). They can be introduced in step (1) all at once or by continuous injection prior to the start of step (2). The oxidant (D′) can be introduced in the reactor from the beginning of step (1) or during step (1), all at once or by continuous injection.
The process of the invention employs (D) at least one oxidant whose solubility in water is at least 10 g/l, at least one of which can be one of (B).
By the expression at least one oxidant (D), it is intended to mean that the process of polymerization may employ one or several oxidants (D).
In the text that follows, the expression “oxidant” used in the singular or plural is to be understood as denoting one or several oxidants, unless denoted otherwise.
By oxidant (D), it is intended to denote any compound which is capable of oxidizing iodide ions to molecular iodine; in other words, which is capable of bringing about an oxidation-reduction reaction with iodide ions in which the iodide ions are oxidized to molecular iodine and in which the oxidant is reduced to its reduced form, i.e., a compound which possesses a redox potential greater than that of the I₂/I⁻ pair (0.53).
The oxidant (D) of the invention has a solubility in water of at least 10 g/l, preferably at least 20 g/l, and particularly preferably at least 30 g/l.
Among the oxidants (D) whose solubility in water is at least 10 g/l, particular mention may be made of sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, compounds generating the MnO₄ ⁻, CIO⁻, CIO₂ ⁻, CIO₃ ⁻ ions, the salts of manganese (III) and the salts of iron (III), e.g. ferric citrate, ammonium/ferric citrate, ammonium/ferric sulfate, ferric acetylacetonate, ferric bromide, ferric phosphate and ferric pyrophosphate.
Preference is given to sodium persulfate, potassium persulfate, ammonium persulfate and hydrogen peroxide.
The expression at least one oxidant of which at least one can be one of (B) means that at least one of the oxidants (D) is one of the free-radical initiators (B), in particular one of the water-soluble free-radical initiators (B), or that none of the oxidants is one of the free-radical initiators (B), particularly one of the water soluble free-radical initiators (B).
According to the process of the invention, it is advantageous to lower the acid pH of the aqueous phase to improve the yield of the reaction.
The manner of introducing the oxidant(s) (D) into the process of the invention can be variable. The entirety of (D) can be introduced in step (1) or a fraction thereof can be introduced in step (1) and the remainder in step (2). Preference is given to the introduction taking place continuously. Preference is given to the introduction in step (2) taking place continuously.
Preference is given to the entirety of (D) being introduced into the reactor between the start of step (1) and the time of step (2) when the degree of conversion reaches 70%.
According to a first preferred embodiment, the process of the invention is either a process of polymerization in aqueous suspension or a process of polymerization in aqueous microsuspension, preferably in aqueous suspension, for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer, one of which is employed as principal monomer and is selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one oil-soluble free-radical initiator selected among oil-soluble diazo compounds and oil-soluble peroxides,
(C) molecular iodine, and
(D) at least one oxidant whose solubility in water is at least 10 g/l, none of which is one of (B); comprising the steps according to which
(1) at least a fraction of each of the compounds (A), (B), (C), and (D) is introduced into a reactor; and
(2) the contents of the reactor are reacted while introducing any remainder of each of the compounds (A), (B), (C), and (D).
The characteristics generally defined above in the context of the process of the invention are applicable to the first preferred embodiment of the process of the invention.
In the particular case of the first preferred embodiment of the process of the invention, the free-radical initiator being oil-soluble, the process employs (D) at least one oxidant whose solubility in water is at least 10 g/l.
In the particular case of the first preferred embodiment of the process of the invention, advantageously, none of the oxidants is one of the free-radical initiators (B).
In the particular case of the first preferred embodiment of the process of the invention, preference is given to employment of only one oil-soluble free-radical initiator (B).
According to this first preferred embodiment, preference is given to employment of only one oxidant as oxidant (D). Preference is given to the oxidant (D) being hydrogen peroxide.
According to this first preferred embodiment, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and where it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, preference is given to the added oxidant (D′) being hydrogen peroxide.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)), based on the number of moles of molecular iodine, is preferably at least 0.5, particularly preferably at least 1.5, very particularly preferably at least 2 and especially very particularly preferably at least 3. A ratio of at least 4 is particularly advantageous.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)), based on the number of moles of molecular iodine, is preferably at most 10, particularly preferably at most 9.
According to a second preferred embodiment, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing

- (A) at least one ethylenically unsaturated monomer, one of which is employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,

(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) at least one oxidant whose solubility in water is at least 10 g/l, of which one may be one of (B); which comprises the steps according to which
(1) at least a fraction of each of the compounds (A), (B), (C), and (D) is introduced into a reactor; and
(2) the contents of the reactor are reacted, while introducing any remainder of each of each of the compounds (A), (B), (C), and (D).
The characteristics generally defined above in the context of the process of the invention are applicable to the second preferred embodiment of the process of the invention.
According to the second preferred embodiment of the process of the invention, at least one of the oxidants (D) may be one of the water-soluble free-radical initiators (B), and preference is given to at least one of the oxidants (D) being one of the water-soluble free-radical initiators (B).
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) and free-radical initiators (B) based on the number of moles of molecular iodine is preferably at least 1.5, particularly preferably at least 2, very particularly preferably at least 2.5, and especially very particularly preferably at least 3. A ratio of at least 4 is particularly advantageous.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) and free-radical initiators (B) based on the number of moles of molecular iodine is preferably at most 11, particularly preferably at most 10.
According to a particularly preferred first variant of the second preferred embodiment of the process of the invention, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing

- (A) at least one ethylenically unsaturated monomer, one of which is employed as a principal monomer and is chosen among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,

(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) an oxidant whose solubility in water is at least 10 g/l and which is one of (B), and comprising the aforementioned steps (1) and (2).
According to a first subvariant of the first particularly preferred variant, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer, one of which is employed as principal monomer and is selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) an oxidant whose solubility in water is at least 10 g/l which is (B), and comprising the aforementioned steps (1) and (2), Preference is given to selection of the free-radical initiator and oxidant among sodium persulfate, ammonium persulfate, and potassium persulfate.
According to this first subvariant, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, the oxidant (D′) can be the free-radical initiator (B) and oxidant (D) or an oxidant (D′) other than (B), such as, for example, hydrogen peroxide. Preference is given to the oxidant (D′) being the free-radical initiator (B) and oxidant (D).
According to a second subvariant of the first particularly preferred first variant, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer, one of which is employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) an oxidant whose solubility in water is at least 10 g/l and which is one of (B), and comprising the aforementioned steps (1) and (2),
Preference is given to selection of one of the free-radical initiators among ammonium 4,4′-azobis(4-cyanovalerate), sodium 4,4′-azobis(4-cyanovalerate), and potassium 4,4′-azobis(4-cyanovalerate) and to the other, which is also the oxidant (D), being hydrogen peroxide.
According to this second subvariant, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, preference is given to the oxidant (D′) being the oxidant (D), with particular preference therefore being given to hydrogen peroxide.
Preference is given to the first subvariant over the second subvariant.
According to a second preferred variant of the second preferred embodiment of the process of the invention, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) two oxidants whose solubility in water is at least 10 g/l, each one being the one of (B), comprising the aforementioned steps (1) and (2),
According to this second variant of the second preferred embodiment of the process of the invention, the process employs a persulfate selected among sodium persulfate, ammonium persulfate, and potassium persulfate, and hydrogen peroxide. According to this second variant, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, the oxidant (D′) can be one of the two oxidants (D) or an oxidant other than the two oxidants (D). Preference is given to the oxidant (D′) being one of the two oxidants (D), particular preference therefore being given to one of the aforementioned persulfates or hydrogen peroxide.
According to a third variant of the second preferred embodiment of the process of the invention, the process of the invention is a process of polymerization in aqueous emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) an oxidant whose solubility in water is at least 10 g/l and which is not the one of (B), and comprising the aforementioned steps (1) and (2).
According to a third preferred embodiment, the process of the invention is a process of polymerization in aqueous mini-emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one oil-soluble free-radical initiator selected among oil-soluble diazo compounds and oil-soluble peroxides and/or at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,

(C) molecular iodine, and

(D) at least one oxidant whose solubility in water is at least 10 g/l, at least one of which can be one of (B);
comprising the steps according to which
(1) at least a fraction of each of the compounds (A), (B), (C), and (D) is introduced into a reactor; and
(2) the contents of the reactor are reacted, while introducing any remainder of each of the compounds (A), (B), (C), and (D).
The characteristics generally defined above in the context of the process of the invention are applicable to the third preferred embodiment of the process of the invention.
According to a first preferred variant of the third preferred embodiment, the process of the invention is a process of polymerization in aqueous mini-emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one oil-soluble free-radical initiator selected among oil-soluble diazo compounds and oil-soluble peroxides,
(C) molecular iodine, and
(D) at least one oxidant whose solubility in water is at least 10 g/l, none of which is one of (B), and comprising the aforementioned steps (1) and (2).
According to this first preferred variant, the free-radical initiator being oil-soluble, the process employs (D) at least one oxidant whose solubility in water is at least 10 g/l.
According to this same variant, advantageously, none of the oxidants is one of the free-radical initiators (B).
According to this same variant, preference is given to employment of a single oil-soluble free-radical initiator (B). Furthermore, preference is given to employment of a single oxidant as the oxidant (D). Preference is given to the oxidant (D) being hydrogen peroxide.
According to this first preferred variant of the third embodiment, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and where it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, preference is given to the added oxidant (D′) being hydrogen peroxide.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) based on the number of moles of molecular iodine is preferably at least 0.5, particularly preferably at least 1.5, very particularly preferably at least 2, and especially very particularly preferably at least 3. A ratio of at least 4 is particularly advantageous.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) based on the number of moles of molecular iodine is preferably at most 10, particularly preferably at most 9.
According to a second variant of the third preferred embodiment, the process of the invention is a process of polymerization in aqueous mini-emulsion for the preparation of polymers employing
(A) at least one ethylenically unsaturated monomer employed as a principal monomer and selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,
(B) at least one water-soluble free-radical initiator selected among water-soluble diazo compounds and water-soluble peroxides,
(C) molecular iodine, and
(D) at least one oxidant whose solubility in water is at least 10 g/l, at least one of which is one of (B), and comprising the aforementioned steps (1) and (2).
According to this second variant, the free-radical initiator being water-soluble, the process employs (D) at least one oxidant whose solubility in water is at least 10 g/l, at least one of which is one of (B).
According to this same variant, preference is given to employment of a single water-soluble free-radical initiator (B). On the other hand, preference is given to employment of a single oxidant as the oxidant (D). Particular preference is given to the water-soluble free-radical initiator and the oxidant (D) being the same compound. The particularly preferred oxidant (D) and free-radical initiator (B) is selected among sodium persulfate, potassium persulfate, and ammonium persulfate.
According to this second variant of the third embodiment, in the illustrative case where molecular iodine (C) is employed in the form of a precursor and where it is then necessary to add an oxidant (D′) to the polymerization medium to generate the iodine, preference is given to the added oxidant (D′) being the free-radical initiator (B) and the oxidant (D).
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) and free-radical initiators (B) based on the number of moles of molecular iodine is preferably at least 1.5, particularly preferably at least 2, very particularly preferably at least 2.5, and especially very particularly preferably at least 3. A ratio of at least 4 is particularly advantageous.
The total number of moles of oxidants (oxidant (D) and optionally oxidant (D′)) and free-radical initiators (B) based on the number of moles of molecular iodine is preferably at most 11, particularly preferably at most 10.
To react the contents of the reactor according to step (2), means by which the radicals are generated within are employed. To this end, the contents can notably be heated or exposed to intense light radiation.
The temperature at which the contents of the reactor are reacted is advantageously at least 30° C. and preferably at least 40° C. Furthermore, it is advantageously at most 200° C. and preferably at most 120° C.
Advantageously, step (2) is continued until the ethylenically unsaturated monomer(s) have reacted within certain limits. Step (2) is continued until the degree of conversion of the ethylenically unsaturated monomer(s) is preferably at least 82%. Step (2) is continued until the degree of conversion of the ethylenically unsaturated monomer(s) is preferably at most 100%.
The process of free-radical polymerization for the preparation of polymers of the invention may optionally comprise another step (3) during which the reaction is terminated by introducing a chemical agent capable of decomposing the excess free-radical initiator and/or by extracting the unreacted fraction of (A), said operations being capable of being carried out simultaneously or successively, within or outside of the reactor.
When the unreacted fraction of (A) has sufficient volatility, it is advantageously extracted from the contents of the reactor by vacuum suction and/or by steam distillation.
The process of free-radical polymerization for the preparation of polymers of the invention may optionally comprise another step, after the above-mentioned steps, wherein the polymer is isolated from the contents of the reactor (step (4)).
To isolate the polymer from the contents of the reactor, besides the demonomerization technique already discussed above, any of the separation techniques known to the professional skilled in the art, notably centrifuging and fluidized bed drying (particularly when the polymer was produced by a process in suspension) and drying by atomization or coagulation (particularly when the polymer was produced by a process in emulsion or mini-emulsion) can be employed. These operations are advantageously carried out outside of the reactor.
In the case where the synthesis of block copolymers is envisioned, preference is given to no action being taken on the aqueous dispersion containing the polymer prepared by the process of the invention; said dispersion then being used as such for the process of synthesizing block copolymers of the invention.
A further object of the present invention is a process of free-radical polymerization in aqueous dispersion for the preparation of block copolymers.
To this end, the invention relates to a process of free-radical polymerization in aqueous dispersion for the preparation of block copolymers employing
(A′) at least one ethylenically unsaturated monomer selected among styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinylic pyridine derivatives, vinylsulfonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers, and (E′) at least one polymer selected among the polymers prepared by the process of the invention as described above and among the precursor block copolymers prepared by reacting at least one ethylenically unsaturated monomer as defined in (A′) and at least one polymer selected among the polymers prepared by the process of the invention as described above, which comprises the steps according to which
(1′) at least a fraction of (A′) and at least a fraction of (E′) are introduced into a reactor, then
(2′) the contents of the reactor are reacted, while introducing any remainder of (A′) and any remainder of (E′), and
(3′) the reaction is terminated.
In the event the polymerization is advantageously living, the process for the preparation of block copolymers of the invention advantageously permits preparation of copolymers comprising two blocks by polymerizing (A′) in the presence of a polymer prepared by the process of the invention as described above, and also of copolymers of more than two blocks, say, three blocks by polymerizing (A′) in the presence of a precursor block copolymer already comprising two blocks, and so forth.
The process of free-radical polymerization for the preparation of block copolymers of the invention complies with the same characteristics and preferences as those described above concerning the process of free-radical polymerization for the preparation of polymers of the invention, unless contraindicated or specified otherwise.
The number of ethylenically unsaturated monomers constituting (A′) can be any number.
(E′) can be introduced into the reactor in any form, notably in the form of a powder or an aqueous dispersion, and after having been isolated or not from the contents of the reactor in which it was previously prepared. Preference is given to the introduction of (E′) into the reactor in the form of an aqueous dispersion containing the polymer prepared by the process of the invention; said dispersion then being used as such for the process of synthesizing block copolymers of the invention, without having undergone treatment beforehand.
The number of polymers constituting (E′) can be any number, but preference is given to 1.
Preference is given to the entirety of (E′) being introduced into the reactor in step (1′).
The weight of (E′) based on the weight of (A′) is advantageously at least 0.05, preferably at least 0.1, and particularly preferably at least 0.5. Moreover, it is advantageously at most 19, preferably at most 10, and particularly preferably at most 4.
In the process of free-radical polymerization for the preparation of block copolymers of the invention, at least one free-radical initiator (B′) selected among peroxides, diazo compounds, and dialkyldiphenylalkanes may be introduced optionally into the reactor in step (1′) and/or step (2′). (B′) complies with the same characteristics and with the same preferences as (B), and to whatever degree of preference. Preference is given to introduction of (B′). (B′) can be introduced in its entirety in step (1′), partially in step (1′) and partially in step (2′) or in its entirety in step (2′).
To terminate the reaction (step (3′)), the contents of the reactor, for example, can be cooled and/or a chemical agent capable of decomposing the excess free-radical initiator can be introduced therein, and/or the unreacted fraction of (A′) can be extracted therefrom (demonomerization), said operations capable of being carried out simultaneously or successively, inside or outside of the reactor.
The demonomerization operation can be carried out in the manner described above for step (3). Finally, the process of free-radical polymerization for the preparation of block copolymers of the invention can optionally comprise an additional step (4′) after the previous steps, according to which the copolymer is isolated from the reactor contents. Step (4′) can be carried out in the manner described above for step (4).
The process of free-radical polymerization in aqueous dispersion for the preparation of polymers of the invention has multiple advantages.
It is characterized by a distinct controlled character, despite using well-known monomers having intrinsic susceptibility towards transfer of free-radical activity from growing polymer chains onto the monomers themselves (transfer-onto-monomer reactions) and/or onto non-living polymer chains (transfer-onto-polymer reactions).
When comparison is made with the standard process described in the prior art and using iodine as control agent, the process of the invention makes it possible to improve control of number-average (or weight-average) molecular weight of the polymers prepared in aqueous dispersion, and also their polydispersity. It is therefore worthy to note that the difference between the theoretical molecular weight and the experimental molecular weight is markedly lower than in the case of the prior process.
Another very significant advantage of the process of free-radical polymerization for the preparation of polymers and of the process of free-radical polymerization for the preparation of block copolymers of the invention is that the growth of the polymer chains prepared in aqueous dispersion can be re-started by undertaking a further reaction of the polymers with ethylenically unsaturated monomers identical with or different from those which had been polymerized previously. In this way block copolymers can be prepared. By contrast, according to the “traditional” process of free-radical polymerization, it is usually not possible to synthesize such copolymers.
Another advantage of the process of free-radical polymerization according to the invention is that it does not need to use starting materials which are usually expensive, e.g. iodinated organic chain-transfer agents.
A final advantage specific to the first subvariant of the first particularly preferred variant of the second embodiment is that it is very highly suitable for industrial operation in terms of cost economics and industrial hygiene.
The examples which follow have the purpose of illustrating the invention, without limiting its scope.

Determination of Monomer Conversion

The degree of monomer conversion was determined by gravimetric analysis in an aluminum dish. To this end, a known amount of the aqueous dispersion was weighed out. One grain of inhibitor was then added to this to stop the polymerization, and the water and the residual monomer were evaporated from the material. The dry extract of polymer was recovered after drying in a vacuum at 40° C. and the degree of conversion was calculated according to the following equation: (Esf-Eso)/(Esth-Eso) in which Esf is the final dry extract, Eso is the initial extract and Esth is the theoretical final dry extract at 100% conversion.

Determination of Molecular Weights

Intended molecular weight (M_{n, intended}), for 100% conversion, was determined by applying the formula according to equation (1), i.e.,
(M_{n, intended})=(weight of monomer)/(2×n_{I2, initial})+M_A-I(equation 1) according to which n_{I2, initial}is the number of initial moles of molecular iodine and M_A-Iis the molecular weight of the chain ends (A being the chain end deriving from the free-radical initiator and I being the atom of iodine).
Theoretical molecular weight (M_{n th}) was determined by considering conversion according to M_{n, th}=(weight of monomer)×(monomer conversion)/(2×ni_2,>initial)+M_A-I.
Experimental molecular weight (M_{n, exp}) was determined by steric exclusion chromatography on dry samples dissolved in tetrahydrofuran by means of a Spectra Physics Instruments SP8810 pump equipped with a Shodex RIse-61 refractometric detector, a Milton Roy Ultra-Violet spectrometric detector, and two 300 mm columns temperature-controlled to 30° C. (mixed-C PL-gel 5 μm columns, Polymer Laboratories—molecular weight range: 2×10²-2×10⁶g.mole⁻¹). Tetrahydrofuran was used as eluant at a flow rate of 1 ml.min⁻¹. Calibration was carried out by means of Polymer Laboratories polystyrene standards. The Mark-Houwink coefficients of polystyrene (K=11.4×10⁻⁵dl.g⁻¹, α=0.716) and of poly(n-butylacrylate) (K=12.2×10⁻⁵dl.g⁻¹, α=0.700) were used for the calculations in the case of the polyBuA samples.
The polydispersity index PDI=M_w/M_nis the ratio of the weight-average molecular weight to the number-average molecular weight determined by steric exclusion chromatography.

Determination of Average Diameter

The average diameter of the particles of the aqueous dispersion (d_p) was determined by means of a Nanotrac Particle Size Analyzer 250 (Microtrac Inc.) particle analyser based on back-scattering of light and the Doppler effect.

Materials Used

Styrene (Acros, 99%), n-butyl acrylate (BuA, Aldrich, 99%), and methyl methyl-acrylate (MMA, Aldrich) were purified by distillation in a vacuum before use.
Iodine (I₂, Aldrich, 99.8%), sodium iodide (Nal, Acros 99%), sodium 1-hexadecanesulfonate (Lancaster, 99%), sodium dodecyl sulfate (SDS, Aldrich, 98%), potassium persulfate (KPS, Aldrich, 99%), di(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16S, Akzo Nobel, 95%), hydrogen peroxide (Acros, 30% by weight solution in water), n-hexadecane (Acros, 99%), 4,4′-azobis(4-cyanovaleric) acid (ACPA, Fluka, 98%), soda (Carlos Erba), and hydroethylcellulose (Aldrich, Mv=9000 g.mole⁻¹, DS 1.50, MS 2.5), were used as received. The 2, 2′-azobisisobutyronitrile (AIBN, Fluka, 98%) was purified by recrystallization in methanol. The water was deionized by passage through ion exchange columns.

EXAMPLE 1 (ACCORDING TO THE INVENTION)

120 g water were placed into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The temperature of the reaction medium was controlled to 85° C., with stirring at 250 rpm. A solution of sodium 1-hexadecanesulfonate (0.031 g, M=328.49 g.mole⁻¹, 0.094 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of 12 (0.3815 g, M=253.81 g.mole⁻¹, 1.5 mmole) in BuA (15 g; M=128 g.mole⁻¹, 117 mmole). Finally, a solution of KPS (1.8 g, M=270.31 g.mole⁻¹, 6.65 mmole) in 20 g water was added and the polymerization was conducted under argon, with the exclusion of light, for 17 hours.
The molar ratio [KPS]/[I2], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 1.

EXAMPLE 2 (ACCORDING TO THE INVENTION)

120 g water were placed into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The temperature of the reaction medium was controlled to 85° C., with stirring at 250 rpm. A solution of sodium 1-hexadecanesulfonate (30 mg, M=328.49 g.mole⁻¹, 0.0913 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of I₂(190 mg, M=253.81 g. mole⁻, 0.748 mmole) in BuA (15 g, M=128 g. mole⁻, 117 mmole). Finally, a solution of KPS (907 mg, M=270.31 g. mole⁻¹, 3.35 mmole) in 20 g water was added and the polymerization was conducted under argon, with the exclusion of light, for 8 hours.
The molar ratio [KPS]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 1.

EXAMPLE 3 (ACCORDING TO THE INVENTION)

120 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The temperature of the reaction medium was controlled to 85° C., with stirring at 250 rpm. A solution of sodium 1-hexadecanesulfonate (30 mg, M=328.49 g.mole⁻¹, 0.0913 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of I₂(96.1 mg, M=253.81 g.mole⁻¹, 0.378 mmole) in BuA (15 g; M=128 g.mole⁻¹, 117 mmole). Finally, a solution of KPS (452 mg, M=270.31 g.mole⁻¹, 1.67 mmole) in 20 g water was added and the polymerization was conducted under argon, with the exclusion of light, for 22 hours.
The molar ratio [KPS]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 1.

EXAMPLE 4 (ACCORDING TO THE INVENTION)

110 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The temperature of the reaction medium was controlled to 85° C., with stirring at 250 rpm. A solution of sodium 1-hexadecanesulfonate (30 mg, M=328.49 g.mole⁻¹, 0.0913 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Nal (227 mg, M=149.89 g.mole⁻¹, 1.514 mmole) in water (10 g). Butyl acrylate (15 g, M=128 g.mole⁻¹, 117 mmole) was then added. Finally, a solution of KPS (1.164 g, M=270.31 g.mole⁻¹, 4.31 mmole) in 20 g water was added and the polymerization was conducted under argon, with the exclusion of light, for 8 hours.
The molar ratio [KPS]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 1.

TABLE 1

	[KPS]/[I₂]	M_{n, intended}	Time	Conv.		M_{n, exp}		d_p
Ex	(molar)	(g · mol⁻¹)	(hr)	(%)	M_{n, th}(g · mol⁻¹)	(g · mol⁻¹)	PDI	(nm)

1	4.4	5200	17	80	4200	5200	1.52	292
2	4.5	10,300	8	99	10,200	9800	1.8	83
3	4.4	20,100	22	86	17,400	20,500	2.28	111
4	5.7	9900	8	77	7600	7300	1.97	111

It can be seen in table 1 that the experimental molecular weight is either less than the theoretical molecular weight or slightly higher than the theoretical molecular weight; thus indicating a very good control of the polymerization.

EXAMPLE 5 (COMPARATIVE)

120 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The temperature of the reaction medium was controlled to 85° C., with stirring at 250 rpm. A solution of SDS (59 mg, M=228.28 g. moles⁻¹, 0.205 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of 1₂(191 mg, M=253.81 g. mole⁻¹, 0.753 mmole) in BuA (15.22 g; M=128 g. mole⁻¹, 119 mmole). Finally, a solution of ACPA (358.8 mg, M=280.28 g. moles⁻¹, 1.28 mmole) neutralized with soda (0.104 g, M=40 g. moles⁻¹, 2.6 mmole) in water (20 g) was added and the polymerization was conducted under argon, with the exclusion of light, for 7 hours. The pH measured at the end of the experiment after recovery of the aqueous dispersion was 5.2.
The intended molecular weight (M_{n, intended}) was 10,400 g. mole⁻¹, the polymerization time was 7 hours, the degree of conversion was 99%, the theoretical molecular weight (M_n>th) was 10,300 g.mole⁻¹, the experimental molecular weight (M_njexp) was 31,000 g. moles, the polydispersity index (PDI) was 1.97 and the average diameter of the particles of the aqueous dispersion (d_p) was 106.
The experimental molecular weight obtained was much higher than the theoretical molecular weight, thus indicating a poor control of the polymerization in this example where no oxidant was added.

EXAMPLE 6 (ACCORDING TO THE INVENTION)

A polyBuA-b-[poly(BuA-co-styrene)] block copolymer was prepared by styrene-seeded polymerization.
Thus, 40.45 g (0.64 mmole) of the aqueous dispersion obtained in example 1 (80% degree of conversion) were introduced into a 100 ml glass reactor and purged by argon bubbling for 20 minutes. A solution of AIBN (0.0182 g, M=164 g.mole⁻¹, 0.11 mmole) in styrene (5.02 g, M=104 g.mole⁻¹, 48.3 mmole) was added to the aqueous dispersion serving as a seed latex. The reaction medium was stirred for 1 hour and the polymerization was conducted under argon, with the exclusion of light, for 14 hours at 75° C.
The intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI) measured on the obtained block copolymer are given in table 2 along with the average diameter of the particles of the aqueous dispersion (d_p).
The theoretical molecular weight (M_{n, th}) was calculated using the equation
M_{n, th}=M_{n, first block}+[(weight of styrene and residual BuA)×degree of conversion (styrene+BuA)/(number of moles of polyBuA-I)]
A good correlation between the theoretical molecular weight (taking into account the monomer conversion in the second block) and the experimental molecular weight was noted, indicative of the living nature of the polyBuA obtained in example 1.

TABLE 2

	Time	Conv.	M_{n, intended}	M_{n, th}	M_{n, exp}
Ex	(hr)	(%)	(g · mol⁻¹)	(g · mol⁻¹)	(g · mol⁻¹)	PDI

6	14	89	14,200	12,600	13,200	1.45

EXAMPLE 7 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (1.495 mg, M=398.5 g.mole⁻¹, 3.75 mmole), of I₂(0.3833 g, M=253.81 g.mole⁻, 1.51 mmole), and n-hexadecane (0.45g; M=226.45 g.mole⁻¹, 1.99 mmole) in styrene (15 g, M=104 g.mole⁻¹, 144 mmole). Finally the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 5 min, 8 KHz) under a stream of argon and the mini-emulsion was purged for 15 minutes more with argon. The temperature of the reactor was controlled to 60° C. and the polymerization was conducted under argon, with magnetic stirring and with exclusion of light for 20 hours. An aqueous solution of hydrogen peroxide (0.7 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 6.17 mmole) in 15 g water was injected for 3 hours starting from the beginning of the reaction by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

EXAMPLE 8 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. The reaction medium was purged for 15 minutes with argon. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (746 mg, M=398.5 g.mole⁻¹, 1.87 mmole), of 12 (0.1903 g, M=253.81 g.mole⁻¹, 0.748 mmole) and of n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in styrene (15 g, M=104 g.mole⁻¹, 144 mmole). The solution was then mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 5 min, 8 KHz) under a stream of argon, and the mini-emulsion was purged 15 minutes more with argon. The temperature of the reactor was controlled to 60° C. and the polymerization was conducted under argon with magnetic stirring and with exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.3 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 2.65 mmole) in 15 g water was injected for 3 hours starting from the beginning of the reaction with a 20 ml Terumo syringe. The pH measured at the end of the experiment after recovery of the aqueous dispersion was 3.36.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

EXAMPLE 9 (COMPARATIVE)

Example 8 was replicated with the exclusion of iodine, hydrochloric acid, and hydrogen peroxide, all other conditions being the same. The pH measured at the end of the experiment after recovery of the aqueous dispersion was 4.74.
The polymerization time, the degree of conversion, the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

EXAMPLE 10 (COMPARATIVE)

Example 8 was replicated with the exclusion of hydrochloric acid and hydrogen peroxide and with a Perkadox/iodine ratio of 2 rather than 2.5, all other conditions being the same. The pH of the aqueous phase measured at the end of the experiment after recovery of the aqueous dispersion was 2.36.
The polymerization time, the degree of conversion, the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.
The intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

EXAMPLE 11 (ACCORDING TO THE INVENTION)

Example 8 was reproduced with the exclusion of hydrochloric acid, all other conditions being the same. The pH of the aqueous phase measured at the end of the experiment after recovery of the aqueous dispersion was 6.75 and the polymerization time was 18 hours.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

EXAMPLE 12 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. The reaction medium was purged for 15 minutes with argon. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (375 mg, M=398.5 g.mole⁻, 0.94 mmole), of 12 (0.0952 g, M=253.81 g/mole-⁻¹, 0.375 mmole), and n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in styrene (15 g, M=104 g.mole⁻¹, 144 mmole). The solution was then mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 5 min, 8 KHz) under a stream of argon and the mini-emulsion was purged for 14 minutes more with argon. The temperature of the reactor was controlled to 60° C. and the polymerization was conducted under argon with magnetic stirring and with the exclusion of light for 14 hours. An aqueous hydrogen peroxide solution (0.277 g at a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻, 2.44 mmole) in 15 g water was injected for 3 hours starting from the beginning of the reaction by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 3.

TABLE 3

	[hydrogen
	peroxide]/[I₂]	M_{n, intended}	Time	Conv.	M_{n, th}	M_{n, exp}		d_p
Ex	(molar)	(g · mol⁻¹)	(hr)	(%)	(g · mol⁻¹)	(g · mol⁻¹)	PDI	(nm)

7	4.1	5200	20	76	4000	4900	1.48	339
8	3.5	10,000	16	78	7900	7900	1.46	316
9	n.a.	n.a.	16	85	n.a.	13,300	2.40	204
10	n.a.	10,000	16	72	7200	13,900	1.73	334
11	3.5	9600	18	58	5600	4500	1.35	309
12	6.5	20,200	14	77	15,600	18,200	1.75	301

n.a.: non applicable

According to the results given in table 3, it can be seen that the experimental molecular weight of the polymers obtained from the examples according to the invention 7, 8, and 12 is either similar to, or slightly higher than the theoretical molecular weight, indicating a very good polymerization control.
In contrast, when the experimental molecular weight and theoretical molecular weight values for example 10 (comparative), in which an oxidant was not added, are compared, it can be seen that the control was poor.
The comparison of the results of examples 8 and 11 illustrates that acidification of the aqueous dispersion makes it possible to improve the yield of the polymerization reaction while still retaining good control of the polymerization.
When iodine is excluded (example 9), the PDI is much higher and the polymer obtained does not permit restarting of the chains in order to make a block copolymer from them.

EXAMPLE 13 (ACCORDING TO THE INVENTION)

42.5 g (M=4900 g.mole⁻, 0.55 mmole) of the aqueous dispersion obtained in example 7 (76% monomer conversion) were introduced in a 100 ml glass reactor and purged with argon bubbling for 20 minutes. A solution of AIBN (0.0233 g, M=164 g.mole⁻¹, 0.142 mmole) in styrene (3.01 g, M=104 g.mole⁻¹, 28.9 mmole) was added to the aqueous dispersion serving as a seed latex. The reaction medium was stirred for 1 hour and the polymerization was conducted under argon, with exclusion of light, for 22 hours at 75° C.
The intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), and the polydispersity index (PDI) measured on the block copolymer obtained are given in table 4, along with the average diameter of the particles of the aqueous dispersion (d_p).
The theoretical molecular weight (M_{n, th}) was calculated using the equation
M_{n, th}=M_{n, first block}+[(weight of styrene)×(degree of conversion)/(number of moles of the first block)]
A good correlation between the theoretical molecular weight and the experimental molecular weight was noted, indicating the living nature of the aqueous dispersion obtained in example 7.

TABLE 4

	Time	Conv.	M_{n, intended}	M_{n, th}	M_{n, exp}		d_p
Ex	(hr)	(%)	(g · mol⁻¹)	(g · mol⁻¹)	(g · mol⁻¹)	PDI	(nm)

13	22	82	10,600	8700	8900	1.80	419

EXAMPLE 14 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of AIBN (427 mg, M=164 g.mole⁻¹, 2.6 mmole), of 12 (0.1922 g, M=253.81 g.mole⁻¹, 0.76 mmole), and n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in butyl acrylate (15 g, M=128 g.mole⁻¹, 117 mmole). The reaction medium was then purged for 15 minutes with argon, the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon and the mini-emulsion was purged for 15 minutes more with argon. The temperature of the reactor was controlled to 85° C. and the polymerization was conducted under argon with magnetic stirring with the exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.53 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 4.71 mmole) in 10 g water was injected for 2 hours, the injection being started just before the total decoloration of the reaction medium, by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 5.

TABLE 5

	[hydrogen				M_{n, th}
	peroxide]/[I₂]	M_{n, intended}	Time	Conv	(g ·	M_{n, exp}		d_p
Ex	(molar)	(g · mole⁻¹)	(hr)	(%)	mole⁻¹)	(g · mole⁻¹)	PDI	(nm)

14	6.2	10,100	16	85	8600	9200	2.11	336

EXAMPLE 15 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of AIBN (931 mg, M=164 g.mole⁻¹, 5.67 mmole), of I₂(0.3865 g, M=253.81 g.mole⁻¹, 1.52 mmole), and n-hexadecane (0.45 g; M=226.45 g.mole⁻¹, 1.99 mmole) in butyl acrylate (15 g, M=128 g.mole⁻¹, 117 mmole). The reaction medium was then purged for 15 minutes with argon, the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon and the mini-emulsion was purged for 15 minutes more with argon. The temperature of the reactor was controlled to 85° C. and the polymerization was conducted under argon with magnetic stirring with the exclusion of light for 6 hours. An aqueous solution of hydrogen peroxide (0.97 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 8.56 mmole) in 10 g water was injected for 2 hours, the injection being started just before the total decoloration of the reaction medium, by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 6.

EXAMPLE 16 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid O.1N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of AIBN (0.224 mg, M=164 g.mole⁻, 1.36 mmole), of 12 (0. 0952 g, M=253.81 g.mole⁻¹, 0.375 mmole), and n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in butyl acrylate (15 g, M=128 g.mole⁻¹, 117 mmole). The reaction medium was then purged for 15 minutes with argon, the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon and the mini-emulsion was purged for 15 minutes more with argon. The temperature of the reactor was controlled to 85° C. and the polymerization was conducted under argon with magnetic stirring with the exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.265 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 2.33 mmole) in 10 g water was injected for 2 hours, the injection being started just before the total decoloration of the reaction medium, by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 6.

TABLE 6

	[hydrogen
	peroxide]/[I₂]	M_{n, intended}	Time	Conv	M_{n, th}	M_{n, exp}		d_p
Ex	(molar)	(g · mole⁻¹)	(hr)	(%)	(g · mole⁻¹)	(g · mole⁻¹)	PDI	(nm)

15	5.6	5100	6	72	3700	4800	1.99	338
16	6.21	20,200	16	81	16,400	21,600	2.28	359

EXAMPLE 17 (ACCORDING TO THE INVENTION)

A polyBuA-b-[poly(BuA-co-styrene)] block copolymer was prepared by styrene-seeded polymerization.
40.75 g (M=9200 g.mole⁻¹, 0.32 mmole) of the aqueous dispersion obtained in example 14 (85% monomer conversion) serving as seed latex and a solution of AIBN (0.02 g, M=164 g.mole⁻¹, 0.122 mmole) in styrene (5.14 g, M=104 g.mole⁻¹, 49.4 mmole) were introduced in a 100 ml glass reactor and purged by argon bubbling for 15 minutes. The polymerization was conducted for 20 hours, with magnetic stirring, under argon with exclusion of light at 80° C.
The intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), and the polydispersity index (PDI) measured on the block copolymer obtained are given in table 7, along with the average diameter of the particles of the aqueous dispersion (d_p).
The theoretical molecular weight (M_{n, th}) was calculated using the equation:
M_{n, th}=M_{n, first block}+[(weight of styrene and residual BuA)×(degree of conversion (styrene+BuA))/(number of moles of polyBuA-I)]
A good correlation between the theoretical molecular weight and the experimental molecular weight was noted, indicating the living nature of the aqueous dispersion obtained in example 14.

TABLE 7

				M_{n, th}
	Time	Conv.	M_{n, intended}	(g ·	M_{n, exp}		d_p
Ex	(hr)	(%)	(g · mole⁻¹)	mole⁻¹)	(g · mole⁻¹)	PDI	(nm)

17	20	60	26,900	19,800	19,400	1.77	434

EXAMPLE 18 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (1.06 g, M=398.5 g.mole⁻¹, 2.66 mmole), of I₂(0.1903 g, M=253.81 g.mole⁻¹, 0.75 mmole), and of n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in methyl methacrylate (15 g, M=100 g.mole⁻¹, 150 mmole). The reaction medium was then purged for 15 minutes with argon, the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon. The temperature of the reactor was controlled to 64° C. and the polymerization was conducted under argon with magnetic stirring and with the exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.59 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 5.20 mmole) in 15 g water was injected starting at the beginning of the reaction for 3 hours by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 8.

TABLE 8

	[hydrogen
	peroxide]/I₂]	M_{n, intended}	Time	Conv	M_{n, th}	M_{n, exp}		d_p
Ex	(molar)	(g · mole⁻¹)	(hr)	(%)	(g · mole⁻¹)	(g · mole⁻¹)	PDI	(nm)

18	6.9	10,300	16	86	8900	8800	1.26	293

EXAMPLE 19 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (2.115 g, M=398.5 g.mole⁻¹, 5.3 mmole), of I₂(0.3828 g, M=253.81 g.mole⁻, 1.51 mmole) and of n-hexadecane (0.45 g; M=226.45 g.mole⁻¹, 1.99 mmole) in methyl methacrylate (15 g, M=100 g.mole⁻¹, 150 mmole). The reaction medium was then purged for 15 minutes with argon and the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon. The temperature of the reactor was controlled to 64° C. and the polymerization was conducted under argon, with magnetic stirring and with exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.57 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 5.03 mmole) in 16 g water was injected starting from the beginning of the reaction for 3 hours by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}) the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 9.

EXAMPLE 20 (ACCORDING TO THE INVENTION)

140 g water were introduced into a 250 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 1 ml hydrochloric acid 0.1 N. A solution of SDS (400 mg, M=288.28 g.mole⁻¹, 1.39 mmole) in water (10 g) was added to the reactor under a stream of argon, followed by a solution of Perkadox 16S (0.5233 g, M=398.5 g.mole⁻¹, 1.31 mmole), of 12 (0.0975 g, M=253.81 g.mole⁻¹, 0.384 mmole) and of n-hexadecane (0.45 g ; M=226.45 g.mole⁻¹, 1.99 mmole) in methyl methacrylate (15 g, M=100 g.mole⁻¹, 150 mmole). The reaction medium was then purged for 15 minutes with argon and the solution was mini-emulsified by ultrasound (Bioclock Scientific Vibra Cell 75043, 1.5 min, 8 KHz) under a stream of argon. The temperature of the reactor was controlled to 64° C. and the polymerization was conducted under argon, with magnetic stirring and with exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.39 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 3.44 mmole) in 16 g water was injected
starting from the beginning of the reaction for 3 hours by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), the polydispersity index (PDI), and the average diameter of the particles of the aqueous dispersion (d_p) are given in table 9.

TABLE 9

	[hydrogen
	peroxide]/I₂]	M_{n, intended}	Time	Conv	M_{n, th}	M_{n, exp}		d_p
Ex	(molar)	(g · mole⁻¹)	(hr)	(%)	(g · mole⁻¹)	(g · mole⁻¹)	PDI	(nm)

19	3.33	5300	16	72	3800	4900	1.25	318
20	9.0	19,800	16	80	15,900	17,000	1.37	324

EXAMPLE 21 (ACCORDING TO THE INVENTION)

A solution of hydroxyethylcellulose (0.055 g) in 50 g water was introduced into a 100 ml glass reactor and thoroughly purged with argon for 30 minutes. The reaction medium was acidified by adding 0.5 ml hydrochloric acid 0.1 N. The temperature of the reactor was controlled to 60° C. A solution of Perkadox 16S (591 mg, M=398.5 g.mole⁻¹, 1.48 mmole), of I₂(0.1263 g, M=253.81 g.mole⁻¹, 0.50 mmole) in styrene (10 g M=104 g.mole⁻¹, 96 mmole) was added dropwise under argon to the reaction medium, with vigorous stirring, and the polymerization was conducted under argon, with magnetic stirring and with exclusion of light for 16 hours. An aqueous solution of hydrogen peroxide (0.34 g of a 30% by weight hydrogen peroxide solution in water, M=34 g.mole⁻¹, 3 mmole) in 12 g water was injected for the first 2 hours by means of a Compact Braun infusion pump equipped with a 20 ml Terumo syringe.
The molar ratio [hydrogen peroxide]/[I₂], the intended molecular weight (M_{n, intended}), the polymerization time, the degree of conversion, the theoretical molecular weight (M_{n, th}), the experimental molecular weight (M_{n, exp}), and the polydispersity index (PDI) are given in table 10.

TABLE 10

	[hydrogen				M_{n, th}	M_{n, exp}
	peroxide]/I₂]	M_{n, intended}	Time	Conv	(g ·	(g ·
Ex	(molar)	(g · mole⁻¹)	(hr)	(%)	mole⁻¹)	mole⁻¹)	PDI

21	6	10,100	16	83	8400	7300	1.5

Claims

1. Process of free-radical polymerization in aqueous dispersion for the preparation of polymers, employing

(A) at least one ethylenically unsaturated monomer, one of which is employed as the principal monomer and is chosen from styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinyl pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives, and N-vinyl monomers,

(B) at least one free-radical initiator chosen from diazo compounds, peroxides and dialkyldiphenylalkanes,

(C) molecular iodine, and

(D) at least one oxidizing agent whose solubility in water is at least 10 g/l, of which at least one may be the one of (B);

said process comprising the steps whereby

(1 ) at least one fraction of each of compounds (A), (B), (C) and (D) is introduced into a reactor, and

(2) the contents of the reactor are reacted while introducing into the reactor the remainder, where appropriate, of each of compounds (A), (B), (C) and (D).

2. Process according to claim 1, characterized in that it is a polymerization process in aqueous suspension, employing, in addition to (A) and (C),

(B) at least one oil-soluble free-radical initiator chosen from oil-soluble diazo compounds, and oil-soluble peroxides, and

(D) at least one oxidizing agent whose solubility in water is at least 10 g/l, of which none is the one of (B).

3. Process according to claim 1, characterized in that it is a polymerization process in aqueous emulsion employing, in addition to (A) and (C),

(B) at least one water-soluble free-radical initiator chosen from water-soluble diazo compounds and water-soluble peroxides, and

(D) at least one oxidizing agent whose solubility in water is at least 10 g/l, of which at least one may be the one of (B).

4. Process according to claim 3, characterized in that it employs

(D) one oxidizing agent whose solubility in water is at least 10 g/l, which is the one of (B).

5. Process according to claim 4, characterized in that it employs

(B) one water-soluble free-radical initiator chosen from water-soluble diazo compounds and water-soluble peroxides, and

(D) one oxidizing agent whose solubility in water is at least 10 g/l, which is (B).

6. Process according to claim 4, characterized in that it employs

(B) two water-soluble free-radical initiators chosen from water-soluble diazo compounds and water-soluble peroxides, and

7. Process according to claim 3, characterized in that it employs

(D) two oxidizing agents whose solubility in water is at least 10 g/l, each one being the one of (B).

8. Process according to claim 3, characterized in that it employs

(D) one oxidizing agent whose solubility in water is at least 10 g/l, which is not the one of (B).

9. Process according to claim 1, characterized in that it is a process of polymerization in aqueous mini-emulsion employing, in addition to (A) and (C),

(B) at least one oil-soluble free-radical initiator chosen from oil-soluble diazo compounds and oil-soluble peroxides and/or at least one water-soluble free-radical initiator, chosen from water-soluble diazo compounds and water-soluble peroxides, and

10. Process of free-radical polymerization in aqueous dispersion for the preparation of block copolymers, employing

(A′) At least one ethylenically unsaturated monomer chosen from styrene and its derivatives, acrylic acid and its derivatives, methacrylic acid and its derivatives, dienes, vinyl esters, vinyl ethers, vinyl pyridine derivatives, vinylsulphonic acid and its derivatives, vinylphosphonic acid and its derivatives and N-vinyl monomers, and

(E′) at least one polymer chosen from the polymers prepared by means of the process according to claim 1 and from the precursor block copolymers prepared by reacting at least one ethylenically unsaturated monomer as established in (A′) and at least one polymer chosen from the polymers prepared by the process according to claim 1,

said process comprising the steps whereby

(1′) at least one fraction of(A′) and at least one fraction of(E′) are introduced into a reactor, then

(2′) the contents of the reactor are reacted while introducing into the reactor the remainder, where appropriate, of (A′) and the remainder, where appropriate, of (E′), and

(3′) the reaction is ended.