Verfahren zur Herstellung eines Beschichtungsmittels

Interpolymers of an alkyl methacrylate having up to 6 carbon atoms in the alkyl group and at least one ethylenically unsaturated comonomer, the interpolymer containing at least 30% by weight of said methacrylate ester and at least 0.1% by weight of an ethylenically unsaturated carboxylic acid, are heated with an imine of the formula where R1 to R5 are each hydrogen, or optionally substituted alkyl, aryl, alkaryl or aralkyl, R6 is hydrogen or optionally substituted C1-C6 alkyl and n is 0 or 1, so as to modify carboxyl groups present in the interpolymer. The imination reaction can be effected before, during or after polymerization of the acid monomer (examples illustrate the latter two methods). The carboxyl groups are believed to be modified, to at least some extent, by conversion to amino-ester groups. Preferred imines are alkylenimines having 2 to 4 carbon atoms. The carboxylic acid groups are derived from monomers such as acrylic, methacrylic, crotonic, 3-butenoic, maleic, fumaric, tiglic and itaconic acids; half-esters of dicarboxylic monomers such as mono-n-butyl maleate; and copolymerizable fatty acids such as castor oil acids. Optional comonomers which may be incorporated in the interpolymers include acrylonitrile, methacrylonitrile, styrene, vinyl toluene, alkyl acrylates, additional alkyl methacrylates, hydroxyalkyl esters of acrylic, methacrylic, ethacrylic, crotonic, maleic and fumaric acids, and N-substituted derivatives of acrylamide. The interpolymers are obtained from the monomers by polymerizing in a solvent, e.g. toluene, aliphatic naphtha, mineral spirits, isopropanol, methyl ethyl ketone or mixtures thereof, and in the presence of a catalyst, e.g. cumene hydroperoxide, benzoyl peroxide or azobisisobutyronitrile; in one Example (No. 5), polymerization is effected in the presence of a milled natural rubber solution. The iminated polymers are useful as a film-forming component in coating compositions, for which purpose the polymer contains at least 50% by weight of polymerized alkyl methacrylate; in a modification, part of the alkyl methacrylate content can be contributed by a separate alkyl methacrylate polymer which is included in a blend with the iminated polymer. The coating compositions may also contain the usual ingredients such as solvents, pigments, plasticizers and fillers. Suitable solvents are those mentioned previously for the polymerization reaction; also specified are acetone and ethylene glycol monoethyl et