MXPA96005715A - Suspension procedure for preparing acrylic polymers - Google Patents

Abstract

The present invention relates to a process for the polymerization of acrylic monomers in aqueous suspension, wherein at least one comonomer has a solubility in water of at least 5 g 100 g., To obtain copolymers containing the water-soluble number of up to 60 % by weight in the presence of a radical initiator soluble in the monomer and a polymeric suspension agent selected from the homopolymer of a compound of the formula: (See Formula) wherein: R1 is H or CH3; R2 and R3, equal or different, are C1-C8 alkalis, optionally branched when possible, M is an alkaline or alkaline earth metal or an ammonium and A is HN or NCH3, wherein the aqueous polymerization phase is completely or partially formed by the obtained mother liquors of a polymerization of an acrylic monomer, said mother liquors containing an organic phase formed by the suspending agent and by other products formed during the polymerization, optional They are supplemented with an additional amount of said suspending agent to obtain an aqueous phase containing 0.01-1% by weight of suspending agent and 0.05-5% by weight of the aforementioned products formed during the polymerization.

Description

DESCRIPTIVE MEMORY The present invention relates to the manufacture of spheres of acrylic copolymers. lyes, in particular acrylic polymers containing water-soluble monomers as defined below. It is known to polymerize acrylic monomers in (&eession; by this process a system is carried out in which an acrylic monomer is generally suspended under the form of droplets in a continuous and polyrneized phase using a radical type initiator. The continuous phase is usually water The ratio between the continuous phase (water) and the discontinuous phase (monorne) is generally between 1: 1 and 3: 1. The final product is formed by a suspension of particles of polymer spheres) with 0.1-1 mm diameter easily removed from water by centrifugation. In the practical mode of this type of procedure, it is necessary to use suspension stabilizers which blocks the coalescence of the small rnonomer droplets in the most advanced stages of the polymerization. As suspension stabilizers, hydrosoluble compounds with affinity to the soil are used, which, by placing them at the interface between an organic phase and an aqueous phase, form a protective film that hides the particle formation. At the end of the polymerization, the suspension agent is removed from the surface of the polymer particles by washing with water. The agent suspension is a key factor since its characteristics condition the performances of the complete procedure as much from the point of view of the quality of the final product as from the point of view of the costs of manufacture, depending on the specific consumptions of Arteriales de departure, productivity, etc. Various methods of polymerization in aqueous suspension of acrylic monorials are known in general, among which the one described in the European patent application 457,356, wherein the particular polymers selected from the polylinkers of the compounds of the formula: agents for suspending and stabilizing the aqueous suspension are used, wherein: Ra- = H, CHa; Rs "and R3, identical or different, are H, C -Cβ alkyl, linear or branched when possible and M is an alkali metal or an alkaline earth metal, or copolymers of said compounds with acrylic monomers. Tests performed by the applicant have shown that the suspension polymerization procedures, or the suspension agents indicated in the application for The aforementioned European invention in water / rnonor relationships between 1: 1 and 3: 1 is useful for producing the copolymers which are the subject of the present invention. From the experiments carried out, the applicant has verified that when the monomers soluble in water are copolymerized the stability of the suspension is compromised and the phenomenon of agglomeration occurs which in the case of drastic cases may involve the entire polymer mass and block the agitation in the least of the drastic cases, producing crusting and blockage of polymers on the walls and on the defectors of the polymerization reactors. In any case, these phenomena mean that the process is not industrializable unless the version is critically reduced, for example by operating high water / polymerization and / or polymerization kinetics in any case, the aforementioned modifications will damage productivity. Other organic or inorganic suspending agents are well known in the art, for example polyvinyl alcohol, bidroxyalkyl cellulose, etc .; among the inorganics for example tricalcium phosphate in combination with the so-called extenders (surfactants). However, the disadvantage of these suspension agents is that the polymers obtained show optics not suitable for acrylic fields, for example lighting, automobile lights, signs, etc. Polymerizations in suspension in non-aqueous media (solvents) are also known, however, there are disadvantages due to the higher costs of solvent and problems of recovery and safety of polymers due to the flammability and explosiveness of the solvents. Other systems in the art to produce the of the invention can be in solution: the monomers are dissolved in a suitable solvent and then polyrneized in a radical manner. The copolymers of the invention can be produced with this method, however there is the disadvantage of removing the solvent from the polymer as stated above. Alternative procedures to those in bulk solution, where the solvent is the monomer itself. These procedures, in solution and in handle are generally used continuously from the industrial point of view to obtain superior productivities, the volumes of equipment used being the same compared to a continuous serni procedure. The disadvantage of continuous procedures lies in that they turn out to be not very flexible from the industrial point of view. Generally, the manufacturing volumes of copolymers with water-soluble coronomers have not yet Sticke a continuous dedicated plant. In this case, a continuous release would require frequent campaign changes with large recovery problems of the unreacted monomers of the polymer protected during the campaign transition. The copolymers of the invention can also be produced in emulsion, however there are higher plant and processing costs due to the separation of the emulsion. Furthermore, the polymers obtained turn out to be optically less for the presence of surfactants and / or coagulants. It feels the need to have at disposal an industrial procedure that allows to produce copolirneros that contain the homonorneros soluble in water with high performances combined with good mechanical and optical properties of the acrylic products of high quality and obtained , c-on multipurpose (discontinuous) plants. * It has now been unexpectedly and surprisingly found that this is possible using the procedure described below. The object of the present invention is therefore a process for the polymerization of acrylic monomers in aqueous suspension wherein at least one rnononero has a solubility in water of at least 5 g per 100 g, to obtain copolymers containing the water-soluble substance up to 50% by weight, preferably from 0.5 to 40%, most preferably from 2 to 20% in the presence of a radical initiator soluble in the monomer and in the suspension agent J "tg 'l lirnérica selected from: a ) The polymeric kiln of a compound of the formula: R = > I CI-.2 = C-CO-A-C-CHa-SOaM (I) I I Ra-Rs where: a. is H or CH; a and R ", the same or different, are H or C3-C3 alkyl, optionally branched when possible; 11 is an alkali metal or alkaline earth metal of α-ammonium and A is NH, 0 or NCH 3, b) The cornpolyners of said compound of the formula I with at most 40% by weight of acrylic monomers, characterized in that the aqueous phase of polymerization it is completely or partially formed by the mother liquors obtained from a polymerization of an acrylic resin, even different from that used for the polymer that is intended to be produced, and also without containing a water-soluble co -omer, after the separation of the spheres, said mother liquors containing an organic phase formed by the suspending agent and other products obtained during the polymerization, optionally charged with an additional amount of said suspension agent, to obtain the aqueous phase containing 0.01 -1% by weight of suspending agent and 0.05-5% by weight, preferably 0.05-1.5%, of the aforementioned products formed during the polymerization. The suspension agent is, in fact, in 0.09 to 0.3% co-concentration. The process according to the invention can be carried out with the embodiments suitable for aqueous suspension polymerizations, operating with ratios between the aqueous phase and the common phases generally comprised between 1: 1 and 3: 1, preferably 1.5: 1 and 2.5: 1, in the presence of a molecular weight regulator and a radical polymerization initiator, both soluble in the rnonomer. The reaction temperatures are those at <The decomposition of the initiators occurs, generally ranging from 50 ° C to 120 ° C. The aqueous phase is formed from 10% to 100%, preferably 30-100%, by weight by the mother liquors obtained by a previous polymerization, provided that the minimum concentrations of said suspension agent and said "Other products" obtained during the polymerization are respected. ?! K The mother liquors do not need to come from a polymerization with the same composition of the monomeric phase object of the invention as stated above. Said mother liquors after the separation of the acrylic polymer, for example, by centrifugation or filtration, generally contain, in relation to the region conditions used, from 0.3% to 3% by weight of organic phase (those indicated above as other products) , certain dry residue at 10 ° C. It is possible to re-circulate from 10 to 100% of said mother liquors, optionally 4 Supplementing if necessary with additional amounts of water containing fresh suspension agent. The nonornomeric mixture that can be polymerized according to the process of the present invention is formed: a) one or more Cx-Cß alkyl or alkylacrylates, linear or branched when possible such as, for example, methylmethacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate; bl) one or more water-soluble solvents having solubility in water of at least 5 g per 100 g of water at a temperature of 23 ° C, in amounts generally of 60% by weight at most, preferably 50% such as , for example, acrylic acid, methacrylic acid, acrylarnide, methacrylate ^^ of hydroxyethyl, hydroxypropyl methacrylate; cl) optionally another rnonomer in an amount of 50% by weight at most, such as, for example, styrene, alpha methyl styrene, methacrylonitrile, n-alkyl or aryl-maleinides with the alkyl being from 1 to 10 carbon atoms and the aryl of 6 to 12 carbon atoms, butadiene, styrenesulfonic, N-vinylpyrrolidone. As radical initiators, peroxides, for example, t-butyl peroxy-2-ethylhexate, dibenzoylperoxide peroxide, t-butyl peroxydiethyl acetate, or unstable azo compounds such as, for example, azodiisobutyronityl can be used. As chain transfer agents, alkylthions such as linear or branched alkyl can be employed.

Ca-Caa, preferably C -Ca-s--, such as, for example, n-butanethiol, n-octanotiol, n-dodocanothiol, ter-dodecanothiol, cyclohexanothiol, pinantiol. The stabilizing agents used in the process of the present invention are prepared by furnace-polymerization of the compounds of the formula (I) or by co-polymerization of said compounds of the formula (I) with acrylic monomers in aqueous solution in accordance with which is described in patent EP 457,356 incorporated herein by reference. In particular, the compounds of the formula (I) are, for example, sodium 2-acrylarnido-2-methylpropanesulfonate 2-methacrylamido-2-rnethylpropane sulfate, sodium 2-acrylamido-propansulphonate, 2-acrylarnido-2-ethanesulf - Sodium nato. Compounds of the formula (I) wherein R and R3 are C -Cß alkyl, also branched when possible are preferred. The acrylic monomers that can be co-polymerized with the compounds of the formula (I) can be, for example, methacrylamide, alkali metal or alkaline earth metal salts of methacrylic acid, esters of methacrylic acid with an alcohol With the process of the present invention, it is therefore possible to industrially prepare spheres of the aforementioned composition, that is, containing up to 60% of a water-soluble monomer, preferably a monomer of acrylic type, operating with agonist / mononer ratios even close to one and with polymerization kinetics of about 2 hours with the following Optimum stability of the suspension, without the appearance of undesirable phenomena of agglomeration of the polymer or fouling of the walls of the reactor; - Drastic reduction of processing waters that will be removed - Drastic reduction of specific agent consumption However, it does not modify the good mechanical and optical properties of the polymers thus obtained. Illustrative examples of the invention are given but without limiting the same.

EXAMPLE 1 * Preparation of the suspending agent 120 parts of 40% by weight of NaOH solution and 630 parts of deionized water are charged to a reactor. 250 parts of 2-acrylamido-2-methylpropane-phonic acid (AMPS) are fed slowly, then the pH is adjusted to a scale of 7-8 with small amounts of soda or AMPS. After the solution has been refluxed with nitrogen to remove fß-igene and heated to 50 ° C, 0.075 parts of potassium persulfate and 0.025 parts of sodium rnetabisulfite are added. The polymerization ends in about 60 minutes. It is then diluted with 4000 parts of deionized water to obtain a solution with a dry residue at 160 ° C of 5.5% by weight and a Brookfield viscosity of 4 Pa. measured at 25 ° C.

EXAMPLE 7. (COMPARATIVE) # Preparation of a methyl methacrylate CODO-methacrylic acid The suspension polymetering of methyl methacrylate and methacrylic acid is carried out using as suspension agent the homopolymer of the sodium salt of 2-acrylamido-2-methylpropanesulonic acid obtained in Example 1. 193 parts of deionized water and 7 parts of the solution obtained in Example 1, corresponding to 0.385 ^ Pieces of dry product are placed in a pressure-resistant reactor and are jacketed, shaken. The oxygen is removed by means of nitrogen flow and the solution is heated to 80 ° C. 100 parts of a mixture, also deoxygenated, formed by: methyl methacrylate 90 parts, methacrylic acid 8 parts, methyl acrylate 2 parts, peroxides-2-butyl ethylenexoate 0.25 parts, n-butanitol 0.19 parts are then fed. The reactor is hermetically sealed, put under pressure at 100 KPa under continuous stirring the mixture is gradually heated up to 110 ° C in 120 minutes. An unstable suspension is obtained with partial reactor blocking, the obtained polymer is not usable. The reactor is cleaned by mechanical blocking removal and its subsequent solvent washing.

EXAMPLE 3 (Comparative) # Preparation of Mother liquors The suspension poly-condensation of methyl methacrylate and ethyl acrylate is carried out using an oven-polyole suspension agent or the sodium salt of ~ 2 ~ acrylarnide-2-methylpropansulonic acid obtained in Example 1. 193 parts of deionized water and 7 parts of the solution obtained in Example 1, corresponding to 0.385 parts of dry product is placed in a stirred, pressure and jacketed reactor. The oxygen is removed by nitrogen and the solution is heated to 80 ° C. Then it is fed: methyl methacrylate 98 parts, methyl acrylate 2 parts, peroxides-2-ethylhexanoate t-butyl 0.25 parts, n-butanthiol 0.19 parts. The reactor is hermetically sealed, put under pressure at 100 KPa and under continuous stirring the mixture is gradually heated to 110 ° C in 120 minutes. The reactor is allowed to stand at 110 ° C for 15 minutes, then cooled. The polymer, in the form of waxes, ß, removed from the mother liquors by centrifugation, washed with deionized water and oven dried at 80 ° C. The polymer is passed over a 500 μ sieve and the fraction retained is less than 0.5%. The spheres are transformed by extrusion into granules for injection molding. The characteristics of the granules thus obtained have been reported in table 2. The mother liquors with a dry residue at 160 ° C of about 62% by weight, partially formed by the suspension agent (0.2% by weight) and for the The remaining fraction for other products obtained during the polyrneration, are collected for use in successive polymerization tests. The polymerization reactor, after the test outlet and flushing, appears clean and is therefore suitable for subsequent polymerization.

EXAMPLE 4 Preparation < 3e a copyrighted "Je methacrylate < faith me ilo-methacrylic acid In the same reactor already used in example 2, and with the general operating modes described in said example, the polymerization is carried out in suspension of methyl methacrylate and methacrylic acid using as suspension agent a fraction of the mother liquors that of the polymerization described in Example 3. 200 parts of mother liquors of Example 3 are then charged to the reactor, the solution is heated to 80 ° C and then methyl methacrylate 90 parts are fed, methacrylic acid 8 parts, acrylate methyl 2 parts, t-butyl peroxy-2-ethylexanoate 0.25 parts, butanitiol 0.19 parts. The polymerization is carried out according to the modalities already described in 2. At the end of the polymerization the reactor is left at 110 ° C for 15 minutes, then it is cooled. The polymer, under the form of spheres, is removed from the mother liquors by centrifugation, washed with deionized water and dried in an oven at 80 ° C. The polymer is passed over a sieve of 500 microns and the fraction retained is less than 0.5%. The spheres are transformed by extrusion into granules for injection molding. The characteristics of the granules thus obtained have been reported in Table 2. The polymerization reactor, after the test run and water jet, appears clean, therefore subsequent poly mer is suitable.

EXAMPLES 5-11 The subsequent examples from 5 to 11 are carried out with the same operation modalities of example 4, in the same polymerization reactor using the same composition of the aqueous phase. M 'a composition of the nonurnal phase is reported in table 1, the properties of the polymers obtained are reported in table 2. The polymerization reactor, after the ealida in each test and washing with water jet, seems clean and therefore, it is suitable for a sub-sequential polyrneration.

* - Table 1 é- s > (*) 2-buyl peroxy-2-ethylexanoate (**) n-butantiol (*) ASTM D1925-70Nbrmal. (**) Test thickness 3mm, ASTM D 1003-61 Norpal. (***) (400-900 poi) / test thickness 3 p.m., ASM D10O3-61 Normal.

(****) IS01628-116 Normal. (P) 230 ° C, 3.8 Kg, ISO 1133 Normal. (p *) ISO 360 Normal. (Q **) No spheres produced (blocked reactor).

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the polymerization of acrylic copolymers in aqueous suspension, wherein at least one comonomer has a solubility in water of at least 5 g per 100 g of water, to obtain copolymers containing the. coronorium hydroealuble up to 60% by weight, in the presence of a soluble phosphate of radicals in the rnonuron and of a polymeric solvent agent selected from: a) the homopoiirneros of cornpuestoe of the formula: where: Ra. is H or CH3; Ra and R3, the same or, are H or alkalis of Ca.-CT, optionally branched when it is possible; M is an alkali metal or alkaline earth metal or ammonium and A is NH, 0 or NCHa, b) copolymers of said compound of the formula I with 40% by weight, as well as many acrylics, characterized in that the aqueous phase of polymerization is completely or partially formed by the mother liquors obtained from a polymerization of an acrylic resin, even different from that used for the polymer intended to be produced, and also without containing a water-soluble coronomer, after the separation of the «cones, said mother liquors containing an organic phase is given by the suspending agent and other products obtained during the polymerization, optionally charged with an additional amount of said suspending agent, to thereby obtain an aqueous phase containing 0.01-1% by weight of suspending agent and 0.05% by weight. -5% by weight of the aforementioned products formed during the polymerization.

2. A process for the polymerization of acrylic monomers in an aqueous suspension wherein for the first time a coronary is soluble in water according to claim 1, wherein the aqueous phase contains 0.05-1.5% by weight of water. the other aforementioned products obtained during the polymerization and the suspending agent in a concentration of 0.03 to 0.3% by weight.

3. A process for the polymerization in aqueous suspension of acrylic monomers wherein at least ur. The comonomer is soluble in water according to claims 1 and 2, where the ratio of water to common water is between 1. 5: 1 and 2. 5: 1

4. A process for the polymerization in aqueous suspension of acrylic monomers in which at least one comonornero is soluble in water according to claims 1 and 3 wherein the monomer mixture is formed by: ai) by one or more acrylates or methacrylates Alkyl of Ca-Cß, linealee or fricae when possible, such as, for example, methyl methacrylate, ethyl methacrylate, rnene-propyl tacrilate, isopropyl methacrylate, ethyl acrylate, sec-butyl methacrylate, tert-butyl methacrylate; bl) by one or more water-soluble monomers having solubility in water of at least 5 g in 100 g of water at a temperature of 23 ° C, in amounts generally 60% by weight at most, preferably 50% such as, for example, acrylic acid, methacrylic acid, acrylamide, hydroxyethyl methacrylate, hydroxopropyl methacrylate; cl) optionally another monomer in an amount of 50% by weight at most, such; & amp; no, for example, styrene, alpha-rnetylstyrene, methacrylonitrile, n-alkyl, or aryl-aleimides with the alkyl of 1 to 10 carbon atoms and the aryl of 6 to 12 carbon atoms, butadiene, styrenesulfonic acid, N-vinylpyrrolidone.

5. A process for the polymerization in aqueous suspension of acrylic monomers in which at least one coronornero is soluble in water in accordance with that in which the suspending agent of: 2-acrylarnido-2-rneti lpropansul fonato de sodio Sodium 2-methacrylate-2-rnethylpropansulphonate, 2- acryl sodium lamidopropansul fonate, sodium 2-acrylarnide-2-ethansulfonate.