Compositions and process for making rigid plastic foams of modified vinyl ester resins and silicone compounds

A non-aqueous thermosettable composition for making rigid plastic foams comprising a liquid resin consisting of 30 to 70 weight percent of a vinyl ester resin having pendant phthalate, isophthalate or terephthalate half ester groups and about 70 to 30 weight percent of a copolymerizable vinyl monomer, wherein said vinyl ester resin is prepared by reacting about equivalent amounts of an unsaturated monocarboxylic acid and a polyepoxide and esterifying at least about half of the hydroxyl groups formed from the acid-epoxide reaction to said half ester groups, and as a frothing agent at least about 1 pph of a copolymer containing (a) SiO.sub.2 units, (b) (CH.sub.3).sub.3 SiO.sub.1/2 units and ##EQU2## units wherein the ratio of (b) units to the sum of the (a) and (c) units is about 0.4:1 to 1.2:1 and wherein n has a value of 0 to 2, R.sub.2 is an alkyl group having 1 to 6 carbon atoms, R.sub.1 is an alkylene radical of 1 to 6 carbon atoms and R is hydrogen, an alkyl radical of 1 to 6 carbon atoms or an aminoalkyl radical having 2 to 6 carbon atoms.