Production of polyanhydride epoxide prepolymer compositions

A low molecular weight polyanhydride epoxide prepolymer composition obtained by admixing an epoxy compound containing more than 1,2-epoxy group with a polyanhydride in an amount sufficient to provide from about 0.1 to about 1.3 equivalents of epoxy per anhydride equivalent weight, said polyanhydride having a molecular weight below about 1000 and a softening point within the range of about 111.degree. C. to about 156.degree. C. and being the reaction product of the mass polymerization process, in the absence of a polymerization catalyst, of a maleic monomer selected from the group consisting of maleic acid, maleic anhydride, anhydrides which rearrange to maleic anhydrides and the halo-, aryl-, aralkyl-, alkyl-, or cycloalkyl-substituted derivatives thereof and at least one alkyl-substituted styrene in molar proportions of said maleic monomer relative to said alkyl-substituted styrene of greater than 1:1, said polymerization process being effected by heating at least a major portion of the maleic monomer to a temperature of about 160.degree. C. to about 200.degree. C., adding the alkyl-substituted styrene to said maleic monomer, with agitation, at a rate which permits control of the heat of reaction and continuing the polymerization until essentially all of said maleic monomer and alkyl-substituted styrene have polymerized.