. . . . "t bond, sulfur, divalent hydrocarbon having from 1 to 10 carbon atoms, hexafluorinated isopropylidene, carbonyl, thio, sulfonyl 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 ato" . . .