hydrocarbon radical containing from 6 to 18 carbon atoms, or a divalent cycloaliphatic hydrocarbon radical containing from 3 to about 10 carbon atoms; and R1 is a divalent aromatic radical having from 6 to 30 carbon atoms interrupted by polysiloxane units of the formula: ##STR16## wherein each R5 represents a divalent hydrocarbon radical having 1 to 14 carbon atoms; each R6 is independently selec