rom 1 to 10 carbon atoms, hexafluorinated isopropylidene, carbonyl, thio and sulfonyl; Y5, Y6, Y7 and Y8 are individually one or more divalent radicals selected from the group consisting of hydrogen, chlorine, bromine, lower alkyl and lower alkoxy radical having from 1 to 10 carbon atoms, respectively; R2 is a tetravalent radical selected from the group consisting of an aliphatic radical and alicy