CA1336735C

CA1336735C - Coating compositions

Info

Publication number: CA1336735C
Application number: CA000605457A
Authority: CA
Inventors: Alistair Robert Marrion; Alistair Andrew Finnie
Original assignee: Courtaulds Coatings Ltd
Current assignee: International Paint Ltd
Priority date: 1988-07-18
Filing date: 1989-07-12
Publication date: 1995-08-15
Anticipated expiration: 2012-08-15
Also published as: KR900701864A; JP2882655B2; JPH04500532A; PT91185A; PT91185B; FI101709B1; NO175905C; FI910235A0; AU4042989A; NO910168D0; NO910168L; DK891D0; BR8907523A; MY107049A; WO1990001040A1; AU629846B2; GB8817085D0; ZA895198B; HK4895A; DK891A

Abstract

A coating composition comprises (A) a hydroxy component having at least two free hydroxy groups per molecule and (B) an anhydride component having at least two cyclic carboxylic acid anhydride groups per molecule, at least one of (A) and (B) being a film-forming polymer. The anhydride component (B) contains a catalytically effective amount of pendent amine groups for accelerating the curing reaction between the hydroxy groups of (A) and the anhydride groups of (B). The proportion of amine groups to cyclic carboxylic acid anhydride groups in the anhydride component (B) is no more than 4:1 and the content of free carboxylic acid groups in the anhydride component (B), if any are present, is less than 200 mole per cent based on the amine groups. The coating composition can be used as a clear or pigmented coating on a wide variety of substrates such as metal, wood, glass or plastics.

Description

~ 1 1 336735 ` CO~TING COMl~OSITI~NS

This invention relates to coating compositions and to their production; also to novel polyanhydrides for use therein.

US Patent 445294~ describes a two-pack coating com-position comprising a hydroxy component and an anhydride component, in which the hydroxy component is a polymer having at least two free hydroxyl groups per molecule and also has in its molecule amine groups for accelerating the curing reaction between the hydroxy groups and the an-hydride groups, and the anhydride component is a polymer having at least two cyclic carboxylic acid anhydride groups per molecule. In a less preferred modification the amine groups are present in a separate amine compound rather than on the molecule of the hydroxy component. The coatings of US Patent 4452943 have the advantage that they are ambient-temperature-curing without the use of toxic isocyanates and have been used successfully as finish coats for automobiles, particularly in re-finishing, `and as paints for yachts.

European Patent Application 134691 describes a three-component coating composition comprising a compound having at least two hydroxy groups, a compound having at least two anhydride groups and a compound having at least two epoxide groups.

European Patent Application 259172 describes a coating composition comprising an anhydride polymer and a polymer containing hydroxyalkylamino, hydroxyalkoxyalkylamino, hydroxy-substituted acyloxyalkylamino, hydroxy-substituted polyacyloxyalkylamino, mercaptoalkylamino or oxazolidino groups. One of the polymers comprises a flexible polymer chain and has its functional groups present as terminal *

- . - 2 - 1336735 groups at the end of the flexible polymer chain.

US Patent 3984382 describes a modified cationic vinyl polymer suitable for electrocoating and prepared by 5 reacting a copolymer of maleic anhydride, styrene and an alkyl acrylate with an amino-alcohol and/or a di-functional amine until the modified polymer has no residual anhydride rings, and reacting the product with a monoepoxy compound.

US Patents 3449250 and 3329658 describe an additive which imparts stability and detergency to mineral oil. The additive comprises a copolymer of maleic anhydride and an alpha-olefin which has been partially esterified with an aliphatic alcohol to make the copolymer oil-soluble and in which substantially all of the remainder of the carboxyl 15 groups are imidized.

German Patent 1595333 describes water-soluble polyelectrolytes useful as flocculating agents and retention aids in paper-making and made by reacting a copolymer of an ethylenically unsaturated carboxylic anhydride with a 20 polyamine containing only one primary or secondary amino group, and reacting the reaction product with an epihalohydrin and/or a diepoxide.

A coating composition according to the invention comprises a hydroxy component having at least two free 25 hydroxy groups per molecule and an anhydride component having at least two cyclic carboxylic acid anhydride groups per molecule, at least one of the hydroxy component and the anhydride component being a film-forming polymer, said composition containing a catalytically effective amount of 30 amine groups for accelerating the curing reaction between the hydroxy groups of the hydroxy component and the anhydride groups of the anhydride component, which contains the said amine groups as pendent groups in its molecules. The anhydride component, having at `t~

~ 1 336735 least two cyclic carboxylic anhydride groups per molecule, is characterised in that the polyanhydride contains pendent amine groups, the proportion of amine groups to cyclic car-boxylic acid anhydride groups being no more than 4:1 and the content of free carboxylic acid groups, if any are present, being less than 200 mole per cent based on the amine groups.

The proportion of amine groups to cyclic carboxylic acid anhydride groups in the polyanhydride is preferably at least 0.01:1 and no more than 1.5:1, most preferably 0.01:1 to 1:1. The content of free carboxyl groups is preferably less than 100 mole per cent based on the amine groups; most preferably, free carboxyl groups are substan-tially absent or are present at less than 20 mole per cent based on amine groups.

The coating compositions of the invention have ad-vantages over those described in US Patent 4452948 and European Patent Application 259172. The polyanhydrides of the invention can be used in coating compositions with a wide variety of hydroxy-functional polymers, including unmodified commercial polymers. The coating compositions also have improved stability against photo-degradation compared to many of the coatings of European Patent Ap-plication 259172. The coating compositions of the inven-tion avoid the possibilities of environmental hazard andstickiness of the cured coating which may be encountered using a free amine compound as catalyst.

The amine groups present in the polyanhydride are preferably tertiary amine groups, which are the most effective in catalysing the reaction between the hydroxy and the anhydride groups without giving rise to side reactions.

One preferred type of polyanhydride according to the invention is a polymer containing cyclic carboxylic an-~ 1 336735 hydride groups and N-(dialkylaminoalkyl)-substituted imide groups. Such a polyanhydride can be formed by the reaction of a polymer containing anhydride groups with a less than stoichiometric amount of a polyamine containing a primary amine group and at least one tertiary amine group. The said polymer containing cyclic carboxylic acid anhydride groups is preferably derived from an olefinically unsaturated cyclic carboxylic acid anhydride.

The polymer containing cyclic anhydride groups can for example be a copolymer of an olefinically unsaturated cyclic carboxylic acid anhydride such as maleic, itaconic, citraconic or vinylsuccinic anhydride or vinyl trimellitate anhydride with one or more olefinically unsaturated com-onomers such as an alpha-olefin, for example ethylene or propylene, a vinyl comonomer, for example styrene or a substituted styrene, vinyl acetate or vinyl chloride, or an ester of acrylic or methacrylic acid, for example butyl acrylate, ethyl acrylate, methyl methacrylate or butyl methacrylate. Preferred copolymers contain 10 - 40 per cent, most preferably 20-35 per cent, by weight ma1eic or itaconic anhydride groups and have a molecular weight of 1500 - 30000, e.g. 4000-12000. If the coating is to be used as a decorative top coat it may be preferred to use a vinyl comonomer at a molar ratio of at least 1:1 with respect to the anhydride monomer, as described in US Patent 4798745.

The polymer containing cyclic anhydride groups can alternatively be an anhydride adduct of a diene polymer such as maleinised polybutadiene or a maleinised copolymer of butadiene, for example a butadiene/styrene copolymer.
The maleinised diene polymer is preferably hydrogenated to remove residual unsaturation. Terpene maleic anhydride copolymer resins are a further alternative. An anhydride adduct of an unsaturated fatty acid ester, for example a styrene/allyl alcohol copolymer esterified with an un-saturated fatty acid and maleinised, can also be used.

~ 1 336735 The polymer containing anhydride groups can alternatively be formed by the reaction of a polymer containing thiol groups with an olefinically unsaturated cyclic carboxylic acid anhydride such as maleic anhydride or itaconic an-hydride. The polymer containing thiol groups is preferablythiol-tipped; it can for example be a multi-limbed telechelic polymer formed by reaction of a corresponding hydroxy-tipped polymer with mercaptoacetic acid.

Alternative anhydride-containing polymers can be formed from hydroxy-containing polymers, for example copolymers of hydroxyethyl acrylate or hydroxyethyl methacrylate or styrene/allyl alcohol copolymers, by reac-tion with a tricarboxylic compound capable of introducing anhydride groups, for example as described in European Patent Application 259172. A further alternative type of polymer containing anhydride groups is an adduct of trimel-litic anhydride and a polyol, as described in European Patent Application 134691.

The polyamine which is reacted with the polymer containing anhydride groups is preferably a primary/ter-tiary diamine, for example N,N-dimethylpropane-1,3-diamine ~(CH3)2NCH2CH2CH2NH2), N,N-dimethylethylenediamine, 4-amino -1-(diethylamino)-pentane, N,N-diethylpropane-1,3-diamine, 2-amino-pyridine, 3-amino-pyridine, 4-amino-pyridine or N-(3-aminopropyl)-morpholine. The primary amino group reacts with the anhydride group to form an imide group which has the tertiary amine group in a pendent organic group at-tached to the imide nitrogen atom. The substituted imide groups formed generally have the formula Z Z

O~N~O
I
X

where each Z represents a polymer residue and X is an ~ 6 l 336735 organic group containing a tertiary amino group and is attached to the imide nitrogen atom by a carbon-nitrogen bond. The group X can for example be an aminoalkyl group of the form -A-NR2, where -A- is a straight or branched-chain alkylene group preferably having 2 to 8 carbon atomsand each group R is an alkyl group preferably having 1 to 4 carbon atoms; a heterocyclic ring containing a tertiary nitrogen atom such as 4-pyridyl; or an alkyl group sub-stituted by a heterocyclic ring containing a tertiary nitrogen atom such as a pyridine or morpholine ring. For example, using N,N-dimethylpropane-1,3-diamine Z I z + (CH3)2NCH2cH2cH2NH2 CH2CH2CH2N(cH3)2 where each Z represents a polymer residue.

The reaction between the polymer containing anhydride groups and the diamine can for example be carried out by heating under reflux in an organic solvent which has a boiling point substantially higher than that of water (for example 120 - 180C) or forms an azeotrope with water, with water being removed by distillation during the reaction.
Examples of solvents are esters such as butyl acetate or methoxypropyl acetate, ketones such as methyl isobutyl ketone or aromatic hydrocarbons such as xylene. The anhydride and amine initially react to form an acid amide which may have limited solubility, particularly in hydrocarbon solvents. It may be preferred to add the diamine gradually during the reaction. Alternatively, the reaction can be carried out as a 2-stage reaction in which the acid amide is formed in an initial step and is heated in a solvent, with removal of water, or with a dehydrating ~_ 1 336735 agent such as acetic anhydride or a carbodiimide such as dicyclohexyl carbodiimide.

The proportion of polyamine reacted with the polymer containing anhydride groups is generally no more than 0.8 mole of polyamine per mole of anhydride groups in the polymer and is preferably no more than 0.5 moles/mole so that the resulting polyanhydride contains at least as many anhydride groups as N-(aminoalkyl)-substituted imide groups. Preferably, the molar ratio of diamine to an-hydride groups is 0.1 - 0.5:1, most preferably 0.1-0.33: 1 .

An alternative form of polyanhydride according to the invention can be formed from a polymer of an olefinically unsaturated tricarboxylic acid such as aconitic acid or an anhydride thereof by reaction with an amino alcohol, preferably a tertiary amino alcohol such as N,N-dimethyl ethanolamine. The reaction is carried out under conditions such as to remove water, for example at reflux in an organic solvent of higher boiling point than water and/or azeotroping with water, for example using butyl acetate as solvent.

25 Z I I Z ~ Z I I - CH2 COOH COOH COOH ~C ~C = O

~ ( CH 3 ) 2NCH 2CH 20H
C~OOCH2CH2N ( CH3 ~ C~COOCH2CH2N ( CH3 ) 2 Z I C Z Z IC - Z

O=C ~ ~ C = O -H 2 COOH COOH

~_~ 8 1 336735 This product containing anhydride groups and pendent amino alkyl ester groups may have increased reactivity with hydroxy groups.

A polymer containing anhydride groups and pendent amine groups cannot in general be formed by the copolymerisation of an unsaturated cyclic carboxylic acid anhydride such as maleic anhydride or itaconic anhydride and an unsaturated amine such as a dialkylaminoalkyl acrylate or methacrylate. Such polymerisation forms either a polyacid or a black charge-transfer complex as described by Taylor and Woodward in J. Polymer Science, Part A., Vol.
1,pp 1473-1482 (1963). A polymer containing anhydride groups and pendent amine groups can however be formed by copolymerisation of an olefinically unsaturated dicar-boxylic acid and an olefinically unsaturated amine,preferably a tertiary amine such as a dialkylamino alkyl acrylate or methacrylate under conditions such as to remove water, for example at a temperature above 100C and/or by azeotropic distillation. The preferred olefinically unsaturated dicarboxylic acid is itaconic acid, which can be dissolved in a polar organic solvent such as tetrahydrofuran. The unsaturated dicarboxylic acid solu-tion is preferably added to the polymerisation vessel separately from the amine monomer, which can for example be diethylaminoethyl or dimethylaminoethyl acrylate or methacrylate. The amine monomer can be dissolved in an organic solvent such as an aromatic hydrocarbon, ester or ketone, preferably together with one or more olefinically unsaturated comonomers. The solvent for the unsaturated dicarboxylic acid may be removed by distillation during the polymerisation; the copolymer is more soluble in organic solvents than the acid monomer.

A further alternative type of polyanhydride is a graft copolymer of a polymer containing cyclic carboxylic acid anhydride groups and a polymer containing amine groups.

~ 336735 Such a graft copolymer can be formed if one of the polymers contains olefinic unsaturation (for example resulting from polymerisation of a diene) and grafting is carried out using a free radical peroxide. The polymer containing unsaturation is conveniently a maleinised diene polymer, preferably maleinised polybutadiene, containing residual unsaturation.

The hydroxy- functional component (A) to be reacted with the amine-containing anhydride-functional component (B) is preferably a film-forming polymer and can be selected to give the desired properties in the cured coating. For example, it can be an addition copolymer having pendent hydroxy groups such as an acrylic copolymer containing 5 - 80% by weight, preferably 10-50% by weight, of a hydroxy-containing ester of an olefini-cally unsaturated carboxylic acid, for example a hydroxyalkyl acrylate or methacrylate such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate or hydroxypropyl acrylate. The hydroxy-containing ester can contain further ester linkages orether linkages, for example 2-(beta-hydroxyethoxy)-ethyl acrylate or methacrylate or an adduct of hydroxyethyl acrylate or methacrylate with caprolactone. Examples of olefinically unsaturated monomers which can be copolymer-ised with the hydroxy-containing ester are acrylic esters such as butyl acrylate, methyl methacrylate, butyl meth-acrylate, ethyl acrylate and hexyl acrylate and vinyl compounds such as styrene, vinyl acetate and vinyl chloride. The hydroxy component (A) can be a copolymer containing a polyester segment, for example a graft copolymer of acrylic monomers onto an unsaturated polyester. The acrylic monomers are preferably selected from those mentioned above and include a hydroxy-containing monomer such as a hydroxyalkyl acrylate or methacrylate.
The polyester segment is preferably a low molecular weight (below 1000) polyester derived from a polyol such as ethylene glycol, propylene glycol or trimethylolpropane and 1 33673~
an acid or anhydride such as phthalic anhydride, isoph-thalic acid or adipic acid with a minor amount of an unsaturated acid or anhydride such as maleic anhydride.
The polyester can for example form up to 50% by weight, preferably 5 - 25% by weight, of the graft copolymer.
Coatings prepared using an acrylic hydroxy- functional component or an acrylic polyester graft copolymer hydroxy-functional component have excellent gloss, flow and ap-pearance after spraying.

An alternative method of preparing an addition copolymer having pendent hydroxy groups for use as the hydroxy component (A) is to prepare a copolymer having amide groups, for example acrylamide or methacrylamide units, and to form N-methylol groups on the amide by reaction with formaldehyde.

The hydroxy-functional component (A) can alterna-tively be a telechelic polymer having hydroxy groups at each end of a polymer chain, such as a polyether, aliphatic polyester, silicone, diene polymer, hydrogenated diene polymer, polyurethane, polyisobutylene or polyacrylate.
The use of such a telechelic polymer can give cured coat-ings having high impact- and abrasion- resistance. Such a telechelic polymer preferably contains more than two hydroxy groups per molecule, for example it can be a polyester or polyether having three or four arms each terminated by a hydroxy group. One example of such a hydroxy-terminated polyester sold commercially is a poly-caprolactone tetraol of molecular weight about 1000.
Alternative hydroxy-functional polyesters can be prepared from polyols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexane-dimethanol, diethylene glycol, dipropylene glycol or neopentyl glycol with dicarboxylic components such as phthalic anhydride, isophthalic acid, maleic anhydride and/or adipic, azelaic or sebacic acid and a trifunctional compound such as trimethylolpropane, tri-~, 1 33673S

methylolethane, glycerol or trimellitic anhydride, using anexcess of the polyols to obtain a hydroxy-tipped polymer.
A lactone such as caprolactone or a hydroxy-acid such as hydroxy-caproic acid or dimethylol propionic acid can be included in the polyester-forming reaction. The hydroxy-functional polyester can be an alkyd polyol containing fatty acid moieties. Another suitable hydroxy-functional polyester can be prepared by reacting an epoxide such as ethylene oxide or a glycidyl ether or ester with a dicar-boxylic acid. Various hydroxy-tipped polyethers are sold commercially, for example under the Trade Marks 'Teracol' and 'Terathane', typically having molecular weights in the range 600 - 2400. These are generally formed by the reaction of a polyol such as glycerol, trimethylolpropane or a higher polyol with propylene oxide and/or ethylene oxide or with tetrahydrofuran. Hydroxy-tipped addition polymers, for example hydroxy-tipped polybutadienes or butadiene/styrene or butadiene/acrylonitrile polymers can also be used. Hydroxy-tipped polyurethanes can alterna-tively be used, formed for example from a polyisocyanateand an excess of a polyol component which may comprise a polyether or polyester polyol and a low molecular weight pol yol .

Alternative hydroxy-functional polymers suitable for use as the hydroxy component (A) include amide-containing polyols prepared by the reaction of a polycarboxylic acid or anhydride with a polyol and a diamine or amino alcohol, epoxy polyols prepared by the reaction of glycidyl ethers of polyphenols such as the diglycidyl ether of bisphenol A
with a bisphenol or an aliphatic diol, polyvinyl alcohol, an allyl alcohol polymer such as a styrene/allyl alcohol copolymer optionally containing allyl ether units, cel-lulose or a cellulose derivative, or a hydroxy-functional polyurethane.

The hydroxy-functional component (A~ can alternatively be a non-polymeric polyol or can include a non-polymeric ~, 1 33~3~

polyol such as ethylene glycol; 1,4-butane diol, neopentyl glycol, 1,4-cyclohexane-dimethanol, 2,2-dimethyl-3-hydroxy propyl 2,2-dimethyl-3-hydroxypropionate, diethylene glycol or an alkoxylated bisphenol A.

The coating composition of the invention is generally a two-pack coating in which the hydroxy component(A) and the polyanhydride (B) are stored separately and are mixed shortly before use. The coating can be applied to a substrate by spray, for example conventional airless spray or twin feed spray in which the polymers (A) and (B) are not mixed until the spray head, or by roller or brush.
The coating composition generally has a pot life of at least fifteen minutes when it is to be applied by twin feed spray or at least one hour after mixing when applied by other techniques. The coating is preferably an ambient-temperature-curing coating capable of curing at ambient temperature, for example 10 - 40C, on the substrate to a hard film which is tack-free and resistant to solvent so that it can be overcoated within 24 hours. Maximum hard-ness, solvent-resistance and impact- resistance generally develop over a number of days at ambient temperature, for example 5 - 20 days. Curing can be carried out at tempera-tures above ambient, for example in the range 40 - 180C, particularly 100 - 150C, for shorter times if this is more convenient, for example when coating under factory conditions.

The proportion of anhydride groups in the anhydride component (B) to hydroxy groups in the hydroxy component ~A) is preferably 0.5:1 - 2:1.

The anhydride component and the hydroxy component are each preferably dissolved in a solvent, such as a hydrocar-bon and/or a polar organic solvent, for example xylene or toluene or trimethylbenzene or mixtures thereof with an ester such as butyl acetate or ethoxyethyl acetate or methoxypropyl acetate or with a ketone such as methylisobutylketone or methylisoamylketone. For most uses the polymers (A) and (B) are preferably compatible both in solution and in the absence of solvent so that a clear coating is obtained. For some uses in which tough-ness of the coating is more important than appearance thepolymers may be less compatible so that there is some phase separation as the coating dries, leading to domains of a mixture rich in one polymer in a matrix rich in the other polymer. This can give increased impact-resistance, though with less complete cure because the anhydride and hydroxy components are not stoichiometrically balanced in each phase.

The coating composition usually contains additives such as pigments or fillers, for example opaque or trans-lucent pigments or metallic flake pigments, fillers,plasticisers, antioxidants, UV stabilisers, surfactants or flow control agents including additives for imparting thixotropy or sag resistance or pigment orientation.
These additives can be included in either or both of the components of the paint, although it is preferred to include any pigments or fillers which may contain sig-nificant amounts of absorbed water with the hydroxy com-ponent (A) to avoid reaction with the anhydride.

The coating composition of the invention can be applied to a wide variety of substrates, particularly to rigid substrates such as metal, wood, glass or plastics.
The compositions can be applied over most commercially sold primers. They can be applied by spray, which is generally preferred, brush or roller or by dipping or flow coating.
The coating compositions of the invention are widely useful as top coat paints and are particularly useful as automo-tive paints, including paints for vehicle refinishing.
They can be applied in "clear on base" coating systems in which a pigmented coat is overcoated with a transparent clear coat. The coating compositions of the invention can be used as either the base coat or the clear coat in such coating systems or preferably as both. They can also be applied as clear coats over known base coats such as polyurethane, acrylic or polyester base coats.

The coating compositions of the invention can alterna-tively be formed as powder coatings in some cases, providedthat both the hydroxy component (A) and the anhydride component (B) are solids at temperatures of up to 50C and provided that at least one of (A) and (B) is a synthetic resin having a glass transition temperature in the range 0 - 120C, preferably 40 - 90oC. For use in powder coating the anhydride component (B) preferably does not contain an olefinically unsaturated double bond in the alpha,beta- or beta, gamma-position with respect to any anhydride groups, and if the anhydride component (B) is an addition polymer the anhydride groups are preferably separated from the addition polymer chain by at least one intervening carbon atom. It can be derived from a polyanhydride of this type described in European Patent Application 209377, for example by reaction with a primary/tertiary diamine.

The polyanhydrides of the invention can be used as crosslinking agents for polymers containing hydroxy groups in uses other than coatings. For example, they can be used as crosslinking agents for cellulose. The cellulose can for example be in the form of pulp or in the form of fibres such as regenerated cellulose or cotton fibres. It can be reacted with the polyanhydride by heating a slurry of the cellulosic material in a solution of the polyanhydride in an organic solvent. Alternatively, wood or a wood product can be strengthened by impregnation with a solution of the polyanhydride, or a cellulosic textile material can be sized with a solution of the polyanhydride.

The invention is illustrated by the following Ex-amples, in which parts and percentages are by weight.
Examples 1-3, 7, 10, 12, 14 and 17 are examples of the preparation of amine-functional polyanhydrides according to ~, 1 336735 the invention. Examples 4-6, 8, 9, 11, 13, 15, 16 and 13 are examples of coating compositions according to the invention.

ExamPle 1 l(a) PreParation of Itaconic AnhYdride CoPolYmer Butyl acetate solvent (142 9) was placed in a 5-litre vessel equipped with mechanical stirrer, addition funnel, reflux condenser and gas inlet. The addition funnel contained itaconic anhydride (150.0 9), methyl methacrylate (75.0 9) and styrene (275.0 9). 2,2'-azobismethylbutyro-nitrile (25.09) was added to the above mixture and the whole dissolved in butyl acetate (500 9). The solvent in the reaction vessel was heated to reflux under a nitrogen atmosphere and the contents of the funnel were added slowly with stirring over a period of 3 hours. After complete addition, stirring and heating were maintained for an additional 1.5 hours to complete polymerisation. The resulting polymer, POLYMER A, had a number average molecular weight Mn of 8000 relative to polystyrene, as determined by gel permeation chromotography, and an an-hydride equivalent weight of 389.

1(b) Preparation of Amine-Functional PolYanhYdride Polymer A (92.09) was placed in a 500 ml vessel equipped with mechanical stirrer, addition funnel, Dean and Stark tap and gas inlet, and the addition funnel was charged with N,N-dimethylpropane-1,3-diamine (12.1 9).
The contents of the vessel were heated to reflux under a nitrogen atmosphere and the contents of the funnel were added dropwise with stirring over 2 hours, during which time water of reaction was azeotropically removed. Heating and stirring were maintained for a further 0.5 hour. In total, 2.1 9 of water was collected. The resulting polymer, POLYMER B, had an Mn of 8500 by gel permeation ~_ 1 336735 chromatography, an amine equivalent weight of 856 and an anhydride equivalent weight of 851.

ExamPle 2 2(a) PreParation of Maleic Anhydride CODO1 Ymer A maleic anhydride copolymer was prepared following the procedure of Example 1(a) but substituting an equal weight of maleic anhydride for the itaconic anhydride. The resulting polymer, POLYMER D, had an Mn of 8200 by gel permeation chromatography and an anhydride equivalent weight of 368.

2(b) PreParation of Amine-Functional PolYanhYdride In an identical manner to that detailed in Example 1(b), Polymer D (75.0 g) in butyl acetate solvent (75.0 9) was reacted with N,N-dimethylaminopropylamine (10.2 g).
The resulting polymer, POLYMER E, had an Mn of 8700 by gel permeation chromatography, an amine equivalent weight of 1010 and an anhydride equivalent weight of 979.

ExamDle 3 3(a) PreParation of AnhYdride-Functional PolYmer Dipentaerythritol (1 mole, 254 g), epsilon-caprolac-tone (6 moles, 684 g), and dibutyltin dilaurate (1.0 g) were heated together in xylene (1000 g) at reflux for 4 hours. Mercaptoacetic acid (6 moles, 552 9) was added, and reflux continued with water trapping until 108 g water had been collected. Isopropenyl acetate (100 g) was added, and total reflux was continued for 1 hour to scavenge any residual hydroxy groups.

Solvent and unreacted ester were removed under vacuum to leave 1380 g of a fairly mobile pale yellow oil. Maleic 17 l 336735 anhydride (588 g, 6 moles) and triethylamine catalyst (0.6 g) were added and the mixture was held at below 30OC
with stirring for 4 hours.

3(b) Preparation of Amino-Functional PolYanhYdride Xylene (1500 9) was added to the above reaction product, followed by 4-aminopyridine (2 moles, 188 9) over a 1 hour period. The mixture was raised to reflux and water (36 g) collected over 7 hours. Volatiles were removed under vacuum to reveal 2120 9 of polyanhydride, POLYMER F, as a yellow oil, with an anhydride equivalent of weight 530.

ExamPles 4 - 6 Pentaerythritol (79.9 g) suspended in xylene solvent (1400 g) containing dibutyltin dilaurate (0.75 g) was placed in a 5-litre vessel equipped with mechanical stir-rer, reflux condenser, addition funnel and gas inlet, and the addition funnel was charged with dry epsilon-caprolac-tone (665.7 g). The vessel contents were stirred at reflux under a nitrogen atmosphere and the contents of the addi-tion funnel were added to them slowly over 1 hour. Heatingand stirring were maintained for a further 2 hours and the solvents were removed under vacuum. The resulting polymeric tetraol, POLYMER C, had an Mn of 1272 and a hydroxyl equivalent weight of 318.

Exam~le 4 Polymer B (Example 1) (2.67 parts) in butyl acetate solvent (4.01 parts) was mixed with Polymer C (1.00 part) in butyl acetate (1.00 part) and cast on glass. It was cured at ambient temperature to give a hard, tough, glossy film within 16 hours. After 7 days at room temperature the film had good resistance to methylethylketone (MEK).

~ 1 336735 ExamDle 5 A mixture of Polymer E (Example 2) (3.08 parts) in butyl acetate solvent (4.62 parts) and polymer C (1.00 part) in butyl acetate solvent (1.00 part) was cast on glass and cured at ambient temperature. After 7 days at room temperature the film had good MEK resistance.

ExamDle 6 Polymer F (Example 3) (5.30 parts) was mixed with Polymer C (3.18 parts) in butyl acetate solution and cast on glass. The coating cured at ambient temperature to a hard but highly flexible coating.

ComDarative ExamDle A copolymer of itaconic anhydride was prepared in the same way as Example 1(a) but with a monomer composition itaconic anhydride 13%, methyl methacrylate 20% and styrene 67%. The polymer obtained had approximately the same anhydride equivalent weight as Polymer B.

It was admixed with hydroxy-functional Polymer C and coated on a glass panel as in Example 4. After 7 days at room temperature the coating was soft and dissolved by brief contact with solvents such as xylene or MEK.

ExamDle 7 PreDaration of anhYdride DolYmer Itaconic anhydride (300g), styrene ~5709), methyl methacrylate (1309), "Vazo 67" (Trade Mark) free radical initiator (509) and a solvent mixture of xylene (3009) and N-methyl pyrrolidone (1009) were premixed and run into a refluxing mixture of xylene (4509) and N-methyl pyrrolidone (1509) over four hours. The mixture was held at reflux for a further one hour and cooled to provide a polyanhydride solution having a solids content of 46.6%, an Mn of 3,800 and a weight average molecular weight (Mw) of 7700 (rela-tive to polystyrene).

PreParation of amine-functional PolYanhYdride N,N-dimethyl propane-1,3-diamine (9.29, equivalent to a third of the available anhydride groups) was added dropwise over 15 minutes to the refluxing anhydride polymer solution (2159) in a vessel fitted with a water separator.
Reflux distillation was continued for a further seven hours, when 1.7g of water had been collected. The product had a solids content of 50.0% and an anhydride equivalent weight of 1204.

ExamPle 8 PreParation of acrYlic PolYol Hydroxyethyl acrylate (193.59), methyl methacrylate (403.59), styrene (403,59) and "Vazo 67" initiator (409) were premixed and added dropwise to refluxing butyl acetate (10009) over 3 hours. Reflux was continued for one hour to yield a polymer solution having a solids content of 50%, an Mn of 5200, an Mw of 10300 (relative to polystyrene) and a hydroxyl equivalent weight of 600.

Coatinq comPosition 24.19 of the amine-functional polyanhydride solution of Example 7 and 12.0 9 of the acrylic polyol solution prepared above were mixed and cast as a film on glass at a dry film thickness of 60 microns. The coating was cured by heating at 150C for 3 minutes. The solvent-resistance of the cured coating was tested by rubbing with a cloth soaked in methylethylketone (MEK); the coating was substantially l 33673~
unaffected by 200 MEK double rubs.

Example 9 PreParation of PolYester polYol Trimethylolpropane (1 mole, 134 9), caprolactone (6 moles, 6849) and xylene (4079) were heated at reflux in the presence of tetrabutyltitanate (0.49) for four hours. The xylene was then removed by vacuum distillation to provide a polymer having a solids content of 97%, an Mn of 814 and a hydroxyl equivalent weight of 271.

Coatin~ comPosition 24.1 9 of the amine-functional polyanhydride solution of Example 7 and 2.8 9 of the polyester polyol prepared above were mixed, cast as a film and heat-cured as described in Example 8. The solvent-resistance of the cured coating was 150 MEK double rubs.

ExamPle 10 PreParation of PolYmeric anhYdride Aconitic acid (2239), styrene (8009) and "Vazo 67"
(509) were dissolved in tetrahydrofuran (7809) and added dropwise to refluxing butyl acetate over three hours.
Azeotropic reflux was continued for a further eight hours, removing tetrahydrofuran and water through a packed column, whilst replenishing butyl acetate as necessary to avoid development of high viscosity.

The product was a polymer having a solids content of 50%, an Mn of 3400 and an Mw of 8500 (relative to polystyrene). It showed strong anhydride peaks in its infrared spectrum and its acid value after precipitation and methanolysis was determined as 43.6, indicating sub-stantial incorporation of aconitic residues.

Its calculated anhydride equivalent weight was 780.

PreParation of amine-functional PolYanhYdride Dimethylethanolamine (11.49) was added dropwise to the refluxing polymeric anhydride solution prepared above (2009) over 15 minutes. Azeotropic reflux was continued until 2.3mls of water had been removed and no hydroxyl signal was visible in the infrared spectrum ~8 hours). The resulting polymer had a solids content of 73%. Its amine equivalent weight after precipitation was determined as 783, and its anhydride equivalent weight was 851.

Example 11 11.7 9 of the amine-functional polyanhydride solution of Example 10 and 2.8 9 of the polyester polyol of Example 9 were mixed and cast as a film on glass at a dry film thickness of 60 microns. The coating film was allowed to cure at ambient temperature (about 20C). The solvent-resistance of the coating was tested after 7 days and was found to be 95 ME~ double rubs.

ExamPle 12 Preparation of amine-functional PolYanhYdride Diethylaminoethyl methacrylate (1009), styrene (6309), neopentylglycol dimethacrylate (709), and "Vazo 67" ~50g~
were dissolved in xylene (4009) and used as feed 1.

Itaconic acid (2329) was dissolved in tetrahydrofuran (10009) as feed 2.

Feeds 1 and 2 were separately added dropwise to 22 l 336735 refluxing xylene (4669) and N-methylpyrrolidone (2009) over three hours whilst simultaneously removed tetrahydrofuran by distillation through a packed column. A~eotropic distillation was continued for a further eight hours, replenishing the solvent mixture with butyl acetate as necessary, until the infrared spectrum showed strong anhydride bands and very weak signals due to free car-boxylic acid.

The resulting polymer solution was adjusted to 50%
solids content. The polymer had an amine equivalent weight of 1850 and an anhydride equivalent weight of 560.

ExamPle 13 11.2 9 of the amine-functional polyanhydride solution of Example 12 and 2.89 of the polyester polyol of Example 9 were mixed, cast as a film and allowed to cure at ambient temperature as described in Example 11. The solvent-resistance of the coating after 7 days was 100 MEK double rubs.

ExamPle 14 Preparation of Polymeric anhYdride A proprietary maleinised, anhydride-functional poly-butadiene of calculated anhydride equivalent weight 490 (available from Revertex as "Lithene PM25MA ) (2009), xylene (4009) and palladium metal (0.49) were treated with hydrogen at a pressure of 80 atmospheres and a temPerature of 100C for 12 hours in a rocking autoclave. The vessel was cooled, vented and discharged to provide a solution, after recovery of the palladium by filtration, having a solids content of 33%, an anhydride equivalent weight of 490 and substantially no unsaturation.

PreParation of amine-functional polyanhYdride 23 l 336735 N,N-dimethylpropane-1,3-diamine (1.379, equivalent to 10% of the available anhydride) was added dropwise over 15 minutes to the hydrogenated polyanhydride solution prepared above (2009). The mixture was azeotroped for eight hours and a proportion of the solvent removed by vacuum distilla-tion to provide a polymer having a solids content of 50%, an amine equivalent weight of 5000 and an anhydride e-quivalent weight of 555.

Example 15 PreParation of acrylic polYol Hydroxyethyl methacrylate (130.09), methyl methacry-late (4359), styrene (4359) and Vazo 67" (509) were premixed and added dropwise to refluxing butyl acetate (10009) over three hours. Reflux was continued for one hour to yield a polymer solution having a solids content of 54%, an Mn of 4800, an Mw of 9000 (relative to polystyrene) and a hydroxyl equivalent weight of 1000.

11.19 of the amine-functional polyanhydride solution of Example 14 and 18.59 of the acrylic polyol solution prepared above were mixed, cast as a film and heat-cured as described in Example 8. The solvent-resistance of the cured coating was greater than 200 MEK double rubs.

Example 16 ll.lg of the amine-functional polyanhydride solution of Example 14 and 12.09 of the acrylic polyol solution of Example 8 were mixed, cast as a film and heat-cured as described in Example 8. The solvent-resistance of the cured coating was greater than 200 MEK double rubs.

ExamPle 17 PreParation of amine-functional PolYanhYdride Ethyl acrylate (47.19), diethylaminoethyl methacrylate (52 99) and "Vazo 67" (5.09) were mixed and fed into refluxing butyl acetate (lOOg) over three hours. The resulting polymer had an amine equivalent weight of 349.
Lithene PM 25 MA (125.99) was then added, and benzoyl peroxide (11.39) added portionwise over 4 hours. The mixture was held at reflux for a further 4 hours to form a graft copolymer, cooled and discharged. It had a solids content of 70%, an amine equivalent weight of 789 and an anhydride equivalent weight of 879. Whilst grafting was probably not complete, it was sufficient to ensure compatibility.

ExamPle 18 The grafted polymer of Example 17 (12.69) was mixed with the acrylic polyol solution of Example 15 (18.59) and cast onto steel panels. Heat-curing (20 mins at 150~C) produced a hard film, resistant to 70 ME~ double rubs.
Such a coating can be used as a stoving primer.

Claims

1. A coating composition comprising (A) a hydroxy component having at least two free hydroxy groups per molecule and (B) an anhydride component having at least two cyclic carboxylic acid anhydride groups per molecule, at least one of (A) and (B) being a film-forming polymer, characterised in that the anhydride component (B) contains pendent amine groups for catalytically accelerating the curing reaction between the hydroxy groups of (A) and the anhydride groups of (B), the proportion of amine groups to cyclic carboxylic acid anhydride groups in the anhydride component (B) being no more than 4:1 and the content of free carboxylic acid groups present in (B), if any, being less than 200 mole % based on the amine groups.

2. A coating composition according to claim 1, characterised in that the pendent amine groups in the anhydride component (B) are tertiary amine groups.

3. A coating composition according to claim 1 or 2, characterised in that the proportion of amine groups to cyclic carboxylic acid anhydride groups in the anhydride component (B) is 0.1:1 to 1:1.

4. A coating composition according to claim 2, characterised in that the anhydride component (B) is a polymer containing cyclic carboxylic acid anhydride groups and N-(dialkylaminoalkyl)-substituted imide groups.

5. A coating composition according to claim 4, characterised in that the anhydride component (B) is formed by the reaction of a polymer containing cyclic carboxylic acid anhydride groups with a less than stoichiometric amount of a polyamine containing a primary amine group and at least one tertiary amine group.

6. A coating composition according to claim 5, characterised in that the said polymer containing cyclic carboxylic acid anhydride groups is derived from an olefinically unsaturated cyclic carboxylic acid anhydride.

7. A coating composition according to claim 6, characterised in that the said polymer containing cyclic carboxylic acid anhydride groups is a copolymer of an olefinically unsaturated cyclic carboxylic acid anhydride with one or more olefinically unsaturated comonomers.

8. A coating composition according to claim 6, characterised in that the said polymer containing cyclic carboxylic acid anhydride groups is an adduct of an unsaturated cyclic carboxylic acid anhydride and a diene polymer.

9. A coating composition according to claim 4, characterised in that the anhydride component (B) is the reaction product of a polymer of an olefinically unsaturated tricarboxylic acid or an anhydride thereof with an amino alcohol.

10. A coating composition according to claim 2, characterised in that the anhydride component (B) is an addition polymer containing cyclic carboxylic acid anhydride groups and dialkylaminoalkyl groups.

11. A coating composition according to claim 1 or claim 2, characterised in that the anhydride component (B) is a graft copolymer of a polymer containing cyclic carboxylic acid anhydride groups and a polymer containing amine groups.

12. A coating composition according to claim 1, characterised in that the hydroxy component (A) is an addition copolymer having pendent hydroxy groups.

13. A coating composition according to claim 1, characterised in that the hydroxy component (A) is a telechelic polymer having hydroxy groups at each end of a polymer chain.