ving from 1 to 7 carbon atoms, with the proviso that R7 and R8 are not both hydrogen; R9 is an alkyl group having from 1 to 7 carbon atoms; R10 and R11 are hydrogen; R12 and R13 are independently selected from the group consisting of hydrogen, ???CN, ???NHCHO, ???NHCOCH3, and an alkyl group having from 1 to 7 carbon atoms; and the copolymer has a weight average molecular weight greater than about