ay be substituted or unsubstituted, and B4 ; each of R6 -R11, inclusive, independently is a monovalent group selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted; each of a and b independently represents an integer from 0 to about 160 which indicates only the quantity of the respective group present in the additiv