GB2137637A

GB2137637A - Polymers containing anhydride groups

Info

Publication number: GB2137637A
Application number: GB08408849A
Authority: GB
Inventors: Alastair Robert Marrion; Susan Roy; Raymond Leonard Herbert
Original assignee: International Paint Ltd
Current assignee: International Paint Ltd
Priority date: 1983-04-06
Filing date: 1984-04-05
Publication date: 1984-10-10
Also published as: GB2137637B; GB8408849D0

Abstract

A polymer containing cyclic carboxylic acid anhydride groups is prepared by copolymerising an olefinically unsaturated polycarboxylic acid with at least one olefinically unsaturated comonomer, which is in solution in an organic solvent, at elevated temperature to form a copolymer solution. The solution is heated during and/or after polymerisation under conditions such that water is removed from the reaction medium. The polycarboxylic acid contains two carboxylic acid groups which are in such a configuration that the acid is capable of forming a cyclic anhydride and is preferably a dicarboxylic acid, for example itaconic acid.

Description

SPECIFICATION Polymers containing anhydride groups This invention relates to polymers containing cyclic carboxylic acid anhydride groups and to a process for making them.

Polymers containing cyclic anhydride groups are used commercially as curing agents for epoxy resins in coatings, casting compositions and adhesives. Polymers containing cyclic anhydride groups have also been proposed in European Patent Application No. 48,128 for use in coating compositions curing at ambient temperature with a separate component containing hydroxyl groups. Most polymers containing cyclic anhydride groups are based on maleic anhydride but in the compositions of European Patent Application No. 48,128 polymers based on other olefinically unsaturated cyclic carboxylic acid anhydrides, particularly itaconic anhydride, may give films of superior properties.

Maleic anhydride is readily produced commercially by the catalytic oxidation of hydrocarbons such as benzene, butane, or butene.

Other olefinically unsaturated anhydrides, however, are considerably more expensive than the corresponding acids from which they have to be prepared.

A process according to the invention for the preparation of a polymer containing cyclic carboxylic acid anhydride groups comprises copolymerising an olefinicaily unsaturated polycarboxylic acid, in which two carboxylic acid groups are in such a configuration that the acid is capable of forming a cyclic anhydride, with at least one olefinically unsaturated comonomer, which is in solution in an organic solvent, at elevated temperature to form a copolymer solution, in which the solution is heated during and/or after polymerisation under conditions such that water is removed from the reaction medium. The polycarboxylic acid used is preferably a dicarboxylic acid.

An anhydride-containing copolymer according to the invention which is prepared by the copolymerisation of an olefinically unsaturated dicarboxylic acid, in which the carboxylic acid groups are in such a configuration that the acid is capable of forming a cyclic anhydride, and one or more comonomers, preferably has a ratio of cyclic carboxylic acid anhydride groups to carboxylic acid groups of at least 1:1 (that is a ratio of carboxylic groups in anhydride form to carboxylic acid groups in acid form of at least 2:1).

The formation of a polymer containing cyclic carboxylic acid anhydride groups is surprising because previously published papers on the homopolymerisation of itaconic acid have shown that itaconic acid homopolymers decarboxylate rather than form anhydride groups: see Braun and Sayed in Makromol.

Chem. 96, (1966), pages 100-121; Tate in Makromol. Chem. 109, (1967), pages 176-193; and Nagai and Fujiwara in J. Polym. Sci., B7, (1969), pages 177-180.

The process of the invention is particularly suitable for preparing polymers containing itaconic anhydride units from itaconic acid, but other olefinically unsaturated dicarboxylic acids in which the carboxylic acid groups are in such a configuration that the acid is capable of forming a cyclic anhydride can be used, for example citraconic or aticonic acid.

Copolymerisation is preferably carried out using 2-80 per cent, preferably 2-50 per cent by weight of the unsaturated carboxylic acid and 20-98 per cent, preferably 50-98 per cent, by weight of at least one comonomer. Esters of acrylic or methacrylic acid, such as butyl acrylate, ethyl acrylate, methyl methacrylate or butyl methacrylate, preferably form at least part of the commonomer component. Styrene is frequently used as a comonomer, although it preferably forms no more than 50 per cent by weight of the comonomer component. Copolymers containing itaconic or citraconic anhydride units and acrylic ester units, preferably in the weight ratio of 10:90 to 50:50, have the advantage of excellent miscibility with hydroxyl-containing acrylic polymers and coatings formed from these components cure to a hard glossy state.Alternatively, a copolymer containing 2 to 10 per cent by weight itaconic anhydride units, with one or more acrylic esters and optionally styrene as comonomer(s), can be used to form a coating composition with a tertiary amino polyol such as triethanolamine or 2-hydroxyme thyl-2-dimethylamino- 1 , 3-propanediol. A copolymer containing 5-30 per cent by weight itaconic anhydride units can be used with a polyester formed by extending triethanolamine with caprolactone, or with an epoxy resin reacted with diethanolamine.

Polymerisation is preferably carried out at a temperature above the boiling point of water, usually at atmospheric pressure at about 100"C, for example up to 180"C. Temperatures of 115"C-150"C are preferred. The organic solvent used is preferably a hydrocarbon, ester, ketone, ether, or halohydrocarbon and preferably has a boiling point above 100"C at atmospheric pressure. Examples are xylene, butyl acetate, methyl isobutyl ketone and a mixture of xylene with butyl acetate or methyl isobutyl ketone. Polymerisation can be carried out at reflux in the solvents whilst water is distilled off. Under these conditions the carboxylic acid groups are converted at least partly to anhydride groups during polymerisation.The organic solvent is preferably free from hydroxyl groups which might lead to esterification of the carboxyl groups.

Polymerisation can alternatively be carried out at a temperature below the boiling point of water, for example at 60-100"C, under atmospheric pressure, followed by a heating step at above the boiling point of water under conditions such that water is removed. In this case the solvent used for polymerisation can include a solvent boiling at below 100"C which is removed before or during the step of heating to remove water.

Polymerisation is preferably carried out by adding the monomers gradually to the heated solvent over an extended period of time, for example 1 to 5 hours. Dicarboxylic acids such as itaconic acid are substantially insoluble in most non-hydroxylic organic solvents. The dicarboxylic acid is therefore preferably added to the polymerisation reaction as a powder or a slurry. It can for example be added by a screw feeder of a type known for adding powders to reactors, preferably with a control system to ensure regular addition, and may be added continuously or in small increments.

The reaction mixture should preferably be agitated to keep the dicarboxylic acid in suspension until it has undergone polymerisation.

The comonomer(s) and a free radical polymerisation initiator are preferably added continuously as undiluted liquid monomer(s) or dissolved in an organic solvent.

Alternatively the dicarboxylic acid can be added as a solution in water, an alcohol such as ethanol or a cyclic ether such as tetrahydrofuran. Such a solution can be gradually fed to the reaction medium as a separate stream or mixed with other monomers. If such a solution of dicarboxylic acid is used the polymerisation step is preferably carried out at below the boiling point of water followed by heating to above the boiling point of water to remove water.

The invention is illustrated by the following examples: Example 1 Xylene (2050 9) and butyl acetate (500 g) were placed in a multinecked flask equipped with agitator, thermometer, dropping funnel and Dean Stark separator, and heated to reflux.

A mixture of styrene (200 g), methyl methacrylate (200 g), butyl acrylate (200 g) and ditertiarybutyl peroxide (30 g) was added continuously over 3 hours with stirring.

At the same time, itaconic acid (180 g) was added in 36 separate 5 9 portions at 5 minute intervals.

Reflux was maintained at 140-150"C and water removed whilst conversion of vicinal acid groups to cyclic an hydrides was monitored by infrared spectroscopy.

Polymerisation was substantially complete after 4 hours' reflux. The percentage conversion conversion of acid groups to anhydride groups over time was as shown in the following table: Time (hrs) % Conversion 5 40 9 66 11 73 12 76 The product after 1 2 hours' reflux largely comprised a copolymer of itaconic anhydride units with styrene, methyl methacrylate and butyl acrylate units.

Example 2 A mixture of 25 per cent by weight styrene (based on total monomers), 26 per cent methyl methacrylate and 26 per cent butyl acrylate with 3.8 per cent di(tertiary butyl) peroxide was added continuously over 3 hours to a 4:1 by volume mixture of xylene and butyl acetate held at reflux (140-150"C) in a flask equipped with agitator, dropping funnel and Dean Stark separator. 23 per cent by weight itaconic acid was added in equal portions at 5 minute intervals over the same 3 hour period.

Polymerisation was substantially complete after 4 hours. Heating at reflux was continued for 5 more hours. The percentage conversion of acid groups from the itaconic acid to cyclic anhydride groups was 84 per cent after 9 hours.

Claims

1. A process for the preparation of a polymer containing cyclic carboxylic acid anhydride groups comprising copolymerising an olefinically unsaturated polycarboxylic acid, in which two carboxylic acid groups are in such 9 configuration that the acid is capable of forming a cyclic anhydride, with at least one olefinically unsaturated comonomer, which is in solution in an organic solvent, at elevated temperature to form a copolymer solution, the solution being heated during and/or after polymerisation under conditions such that water is removed from the reaction medium.

2. A process according to claim 1, in which the polymerisation is carried out at 115-150"C.

3. A process according to claim 1 or Claim 2, in which water is distilled off during polymerisation.

4. A process according to any of claims 1 to 3, in which polymerisation is carried out by adding the monomers gradually to the heated solvent over a time of 1 to 5 hours.

5. A process for the preparation of a polymer containing cyclic carboxylic acid anhydride groups carried out substantially as hereinbefore described with reference to Example 1.

6. A process for the preparation of a polymer containing cyclic carboxylic acid anhy dride groups carried out substantially as hereinbefore described with reference to Example 2.

7. A polymer containing cyclic carboxylic acid anhydride groups prepared by the process of any of claims 1 to 6.

8. An anhydride-containing copolymer prepared by the copolymerisation of an olefinically unsaturated di-carboxylic acid in which the carboxylic acid groups are in such a configuration that the acid is capable of forming a cyclic anhydride and one or more comonomers, which copolymer has a ratio of cyclic carboxylic acid anhydride groups to carboxylic acid groups of at least 1:1.

9. An anhydride-containing polymer according to claim 7 or claim 8, in which the copolymerisation is carried out using 2 to 50 per cent by weight of the unsaturated dicarboxylic acid and 50 to 98 per cent by weight of at least one comonomer.

10. An anhydride-containing copolymer according to any of claims 7 to 9, in which the unsaturated polycarboxylic acid is itaconic acid.