A functional block copolymer useful as a compatibilizing agent for a blend
of a condensation polymer and vinyl polymer comprises segments of a
condensation polymer and a vinyl polymer derived from a reactive
functional group-containing monomer or a functions-imparting monomer such
as ultraviolet absorption or flame retardant functions. The block
copolymer can further include a segment of a lower cohesive energy
polymer. The condensation or vinyl polymer segment, or the lower cohesive
energy polymer segment contains azo or peroxide groups which act as a
polymerization initiator for the copolymerization of the vinyl monomer
forming the vinyl polymer segment.