"wherein R1 and R1??? each, independently of the other, is an alkyl group, an aryl group, an arylalkyl group, or an alkylaryl group, R2 and R2??? each, independently of the other, is an alkylene group, an arylene group, an arylalkylene group, or an alkylarylene group, R3 is an alkylene group, an arylene group, an arylalkylene group, or an alkylarylene group, and R4 and R5 each, independently of the" . . . .