NL1041960B1 - Catalytically active radical scavengers based on allylic-hydrogen functionalities - Google Patents

Abstract

An inhibitor to prevent oxidative radical degradation via an allylic hydrogen abstraction mechanism, effective in an amount of less than 1% (w/w) based on the solid weight of substrate or substrate composition. The inhibitor comprises a substituted allyl fragment x~:w Y~Z

Description

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The Netherlands

(21) Application number: 1041960 © Application submitted: 29/06/2016

1041960

BI PATENT (Tl) Int. Cl .:

C08K 5/09 (2017.01) C09K 15/06 (2017.01) C08K 5/092 (2017.01)

(Ti) Application registered: (73) Patent holder (s): 05/01/2018 Holland Novochem Technical Coatings B.V. in Houten. (43) Application published: (72) Inventor (s): (w) Patent granted: Alexander Maslow in Deventer. 05/01/2018 Erik Alexander Bijpost in Nieuwegein. (45) Patent issued: 01/02/2018 (74) Agent: O. Griebling in Tilburg.

© Catalytically active radical scavengers based on allylic-hydrogen functionalities (57) An inhibitor to prevent oxidative radical degradation via an allylic hydrogen abstraction mechanism, effective in an amount or less than 1% (w / w) based on the solid weight of substrate or substrate composition. The inhibitor comprises a varied allyl fragment

NL BI 1041960

This patent has been granted regardless of the attached result of the research into the state of the art and written opinion. The patent corresponds to the documents originally submitted.

ref .: P 2016 NL 015

TITLE: Catalytically active radical scavengers based on allylic-hydrogen functionalities

Introduction

It is generally known that many polymers are prone to degradation. Especially for durable outdoor products and rubber tires, the life time is limited due to influence of daylight, UV and ozone, initiating random radical reactions (metastable singlet oxygen as main initiator). Many attempts to prevent degradation, ranging from addition of metal deactivators, UV absorbers, peroxide decomposers, free radical chain stoppers to inhibitor regenerators etc. All these solutions have in common that it is a temporary inhibition, because they will lose activity in time as quenching / trapping occurs radically stoichiometrically.

Separate from polymers, a large group or monomers are prone to oxidation and / or radical-induced reactions. Known examples are styrene, divinylbenzene, acrylates, methacrylates, fatty acids etc. All these compounds have been stabilized to prevent any reaction upon storage. Usually hydroquinones, 2,6-di-tert-butyl-p-cresol (BHT) and the like are applied to stabilize the systems by quenching radicals. These compounds will oxidize to a thermodynamically stable compound. Hence, they act as stoichiometric radical scavengers.

Next to polymers and reactive monomers, many molecules, containing an active abstractable C-H donor, e.g. toluene, xylene, benzyl alcohol, natural oils and corresponding fatty acids will oxidize on aging. These raw materials are not always stabilized.

Proposed mechanism or radical-induced degradation

For polyalkylene radical-induced degradation one can distinguish two major pathways.

A. For linear polyalkylenes an oxygen radical will abstract a hydrogen radical from the polymer chain, forming a secondary reactive carbon radical. This species as such is very reactive, following mainly two pathways, viz. dimerization (cross-linking) and / or hydrogen abstraction from the matrix. Hardly any disproportionation or decomposition will occur. Owing to the dimerization the average molecular weight will increase in time, while the physical properties will change, such as brittleness.

B. For branched polyalkylenes, an oxygen radical will also include a hydrogen radical from the polymer backbone, forming a tertiary stabilized carbon radical. Predominantly an intramolecular disproportionation will take place, such as dezipping. The resulting degradation products will have a lower average molecular weight in time. Change, the physical properties of the polymer will change as well.

Invention

Surprisingly, Applicant found that radical-initiated degradation of polymers, monomers and reactive solvents can be prevented / inhibited catalytically. The origin of the invention has been filed by the Applicant in WO2011 / 008081, describing radical curing coating compositions, including biscitraconimides. Amongst others, it teaches the structural difference between maleimides and citraconimides. It is without saying that this is also valid for the corresponding acids, anhydrides, amides and esters. Although there is a strong chemical resemblance between maleic and citraconic acid, the methyl substituent in citraconic acid gives rise to completely different reaction paths, e.g. isomerization, allylic hydrogen abstraction, Michael addition etc.

These special characteristics have been employed to design an inhibitor, prevent oxidative / radical degradation or several polymers, such as polyethylene, polypropylene, and copolymers and terpolymers as well as functionalized polymers. Even under extreme conditions, eg storage at 200 ° C for 30 minutes under continuous air flow or under ozone treatment by gas high voltage UV lamp, the polymer or polymer compositions maintain its original properties, proven by viscosity, MEK rubbing or thin layers and minimal change in melting peak temperature T _pea k (DSC).

Compounds, such as itaconic acid, citraconic acid and their corresponding anhydrides, and derivatives, such as amides and imides etc, can stabilize the radical-induced degradation reactions as follows (for clarity only itaconic acid has been applied, but it is obvious for those skilled-in -the-art that the mechanism is valid for corresponding compounds as well):

A. For linear polyalkylenes, upon oxidation highly reactive secondary alkyl radicals are formed. They abstract rapidly an allylic hydrogen from itaconic acid or the corresponding alternatives. The linear polyalkylene polymer chain is re-manufactured and remains unaffected. The formed stable allylic itaconic radical will absorb in time a hydrogen radical from the matrix, reestablishing the catalyst. Moreover, the oxygen radical is trapped by itaconic acid, protecting the polyalkylene polymer to be attacked.

B. For branched polyalkylenes, upon oxidation more stable tertiary alkyl radicals are formed. Due to the structural properties, polyalkylenes will predominantly give in-cage (intramolecular) disproportionation / degradation. This is independent of the matrix. Cause, preventing this process the oxygen radical has been trapped before it attacks the polymer backbone via the highly reactive itaconic type or inhibitor. The formed stable allylic itaconic radical will absorb in time a hydrogen radical from the matrix, usually another neutral itaconic type molecule or termination via itaconic dimer formation, reestablishing the catalyst property. It must be noted that intramolecular disproportionation strongly depends on temperature. Upon severe heating (> 200 ° C) for a longer period of time, this thermal degradation process will dominate and the effect of catalytic inhibition will be negligible. Lowering the temperature will strongly diminish this thermally induced degradation process.

The efficiency of the catalytic action to prevent radical-induced degradation is based on allylic hydrogen abstraction, reactivity and stability as well as regeneration or the thermodynamically-favored allylic hydrogen bond. All molecules with an alpha-allylic hydrogen are basically able to inhibit radical-initiated decomposition or polymers. The higher the degree of conjugation the better the stabilization. Aromaticity is the best driving force for catalytic activity or inhibitors and maintenance / stability of the polymers. The inhibitors of choice contain the following functional moiety:

X can be selected from alkyl, aryl, substituted alkyls, substituted aryls, polar functional groups.

Y can be selected from hydrogen, alkyl, aryl, substituted alkyls, substituted aryls, polar functional groups, such as ketones, aldehydes.

W can be selected from oxygen, sulphur, nitrogen-containing groups or phosphor-containing groups.

Z can be selected from hydrogen, alkyl, aryl, hydroxyl, alkoxy, amino, aryloxy, amino derivative or the corresponding salts (ligands).

Typical candidates meeting these criteria are itaconic acid and citraconic acid. They comprise, two and three allylic hydrogen, respectively, making them highly suitable for the catalytic inhibition or the oxidative radical-induced degradation.

The alkene-carboxylic group can form tautomers, giving the stabilization and reactivity to a radical and regenerate the active species. Those skilled in the art know that several carboxylic derivatives, such as amidines, imides, amides can also stabilize allylic radicals.

It is clear for those skilled-in-the-art that the capacity of the catalytic inhibitor is concentration depend. To prevent alkyl radical formation side reaction the concentration of the catalyst should be equal or higher to the amount of the present oxygen radicals. The relative concentration is also dependent on reaction kinetics equilibria or the speed of deactivating the oxygen radical and the rate of reestablishing the catalyst property. The higher the amount of stabilizer the higher the stability and resistance of the polymer or other substrates under extreme oxygen radical attack induced conditions: sunlight, UV, temperature, oxygen, ozone, peroxide, metals and corresponding oxides.

It must be noted that grafted itaconic acid on polymers cannot show the same catalytic activity / polymer stabilization, as the allylic functionality has disappeared due to reaction with the polymer upon grafting. On the other hand, dimers, oligomers and polymers derived from allylic compounds, such as itaconic acid, usually contain an allylic end group. These moieties can be active as an inhibitor for radical scavenging.

Parallel to this invention, Applicant observed also excellent catalytic activity in radical scavenging or the conjugated benzylic molecules. Typical examples are phenol-formaldehyde condensation products, monomers, dimers, oligomers and resins, and triphenylmethane derivatives. These compounds are capable of reestablishing their original form as well as due to the stable thermodynamically favored molecule structure. The conjugated benzylic inhibitors can be combined and / or mixed with the allylic compounds according to this invention. It is evident for those skilled-in-5 molecules that include both an allylic moiety and a benzylic moiety, can show catalytic activity in radical scavenging as well.

Those ski-in-the-art know that catalytic inhibition or radical-induced reactions can be applied to many processes. All polymers in general are susceptible to oxy radical-induced attack / decomposition, e.g., polyethylene, polypropylene, homo and terpolymers as well as functionalized polymers. With the new invention these polymers can be catalytically stabilized instead of using traditional scavengers. In line with this invention, also monomers and reactive solvents, susceptible to oxidation in time upon storage, can be stabilized.

It is evident that also oxygen-containing radicals can be stabilized analogously. Typical examples of such radicals are oxygen, peroxy, aryloxy, alkoxy, alkyl peroxy, arylcarbonate and alkylcarbonate radicals and ozone.

The shelf life of natural oils, fatty acids, food stuff, wine and other beverages can be increased gently by compounds according to this invention as well.

Examples

A 100 ml open glass vessel is charged with 10 grams of polymer. A defined amount or inhibitor is added and thoroughly stirred. The mixture is heated up to 200 ° C in a Gallenkamp box oven. When the polymer has reached the softening point, the mixture is thoroughly stirred again. Then a continuous airflow is passed through the oven, allowing the mixture to come into contact with oxygen. The physical properties are monitored in time. T _pea k values have been determined by DSC (Mettler DSC 12E, 80 ° C-250 ° C, rate: 10 ° C / min).

Polymer Inhibitor (% w / w) Observations 30 min @ 200 ° C Tpeak (° C) PP No heating after. 163 PP 0 Clear slightly yellow liquid 153 PP 1% Itaconic acid Clear yellow liquid 159 PP 0.05% Itaconic acid Clear yellow liquid 158

PP 1% Citraconic anhydride Clear slightly yellow 155 PP 0.05% Itaconic acid + 0.05% Substituted phenol formaldehyde resin Clear yellow 163 LLDPE No heating after. 124 LLDPE 0 Clear liquid slightly yellow 121 LLDPE 0.05% Itaconic acid Clear liquid slightly yellow 122 LLDPE 0.05% Itaconic acid + 0.05% Substituted phenol formaldehyde resin Clear liquid slightly yellow 124

It can be concluded from the examples that radical-induced degradation reactions can be inhibited by functionalized allylic compounds, such as itaconic acid and citraconic anhydride. Even catalytic amounts or inhibitor added show the same activity. Upon mixing and / or combining these compounds with a conjugated benzyl compound, substituted phenol formaldehyde resin, a pronounced catalytic radical scavenging effect can be obtained as well.

Claims (14)

CONCLUSIONS An inhibitor to prevent oxidative radical degradation via an allylic hydrogen extraction mechanism effective in an amount of less than 1% (w / w) based on the solid weight of substrate or substrate composition. A compound according to claim 1, wherein the inhibitor comprises a substituted allyl group, X can be selected from alkyl, aryl, substituted alkyl groups, substituted aryl groups, polar functional groups. Y can be selected from hydrogen, alkyl, aryl, substituted alkyl groups, substituted aryl groups, polar functional groups such as ketones, aldehydes, W can be selected from oxygen, sulfur, nitrogen-containing groups or phosphorus-containing groups, Z can be selected from hydrogen, alkyl, aryl, hydroxyl, alkoxy, amino, aryloxy, amino derivative or the corresponding salts (ligands). A compound according to claims 1 and 2, wherein the inhibitor comprises at least one carboxyl-substituted or aminidine-substituted allyl group. A compound according to any one of claims 1 to 3, wherein a carboxylic acid, ester, amide, imide, aldehyde or ketone is present in the carboxyl substituent. A compound according to any one of claims 1-4, wherein the inhibitor is itaconic acid or citraconic acid. The compound or mixture of any one of claims 1-5, wherein the inhibitor further comprises a conjugated benzyl-stabilized group. The composition of claim 6, wherein the conjugated benzyl stabilized molecule is selected from phenolic monomers, phenolic oligomers, phenolic resins, mono-, bis- or tri-substituted phenol and / or hydroxylated polycyclic aromatic compounds. The composition of any one of claims 1-7, wherein the inhibitor is a mixture of at least two or more inhibitors. The composition of any one of claims 1-8, wherein the substrate is a polymer, monomer or reactive solvent. The composition of any one of claims 1-9, wherein the polymer comprises olefin groups. The composition of any one of claims 1 to 10, wherein the substrate is polyethylene, polypropylene, polybutadiene, polyisoprene, polyhexene or copolymers thereof, or grafted polymers. The composition of any one of claims 1 to 11, wherein the substrate is a monomer selected from acrylate, methacrylate, styrene, divinyl benzene, natural oils or corresponding fatty acids, food, wine, and beverages. The composition of any one of claims 1 to 12, wherein the substrate contains a reactive C-H bond, preferably aromatic, selected from toluene, xylene, cumene, benzyl alcohol or benzaldehyde. Compositions according to one or more of claims 1-13, wherein the inhibitor is effective in less than 0.5% (w / w), preferably less than 0.2% (w / w), and even more at preferably less than 0.05% (w / w) based on the total amount of solids. *