by weight of at least one member selected from the group consisting of(1) an ester having the structure ##STR8## wherein R1 is hydrogen, an alkyl group having from 1 to 4 carbon atoms, or a halogen, and R2 is an alkyl group having from 1 to 6 carbon atoms, and (2) a vinyl ester selected from the group consisting of vinyl acetate, vinyl propionates, vinyl butyrates, isopropenyl acetate, isopropenyl