Solutions of polyester-imides

Claim 1

A polyester-polyimide having a hydroxy to carboxyl ratio of 1.25:1 to 2:1, 95 to 50% ester groups, 5 to 50% imide groups, the polyimide being an imide of reactants comprising a diamine and trimellitic anhydride, the polyester being an ester of isophthalic acid or terephthalic acid with up to 10% of an alkane dicarboxylic acid having 6 to 10 carbon atoms with alcohols wherein 5 to 45% of the hydroxyl groups are contributed by (I) an ether-alcohol which either (a) has the formula RO(C n H 2n O) x H where R is an alkyl group of 1 to 6 carbon atoms or phenyl, n is 2 or 3 and x is 2 or 3 or (b) is the monophenyl ether of ethylene glycol, (II) at least 20% of the hydroxyl group are contributed by a trihydric alcohol and (III) any balance of hydroxyl groups are contributed by a dihydric alcohol, said polyester-polyimide having a sufficiently low molecular weight that it is soluble in a mono lower alkyl ether of diethylene glycol alone or in the monophenyl ether of diethylene glycol or phenoxyethanol or a mixture of said phenyl ethers.