The composition of claim 13 wherein at least one of R1, R2, R7 and R8 is a hydrocarbon radical represented by the formula: ##STR15## wherein R16 and R17 are the same or different and are hydrogen or a substituted or unsubstituted monovalent hydrocarbon residue, R18 is a substituted or unsubstituted divalent or trivalent hydrocarbon residue, and h and i are the same or different and are a value of