and ether; Y1, Y2, Y3 and Y4 are individually a radical selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, chlorine and bromine; and R is a tetravalent radical selected from the group consisting of an aliphatic radical having from 4 to 9 carbon atoms, monocycloaliphatic radical having from 4 to 10 carbon atoms, monoaromatic radical, condensed polyaromatic radical and noncon