product of reactants comprising (a) a 'stilbene dicarboxylic acid com pound of the group consisting of its acids, esters and acid chlorides and (b) at least one bifunctional compound of the group consisting of polyoxyalkylene glycols having the formula where R is an alkylene radical of from about 2 mesmerwhere R, isv an alkylena radical of from about 2 to 6 carbon atoms and nis an integer of from