The synthesis of well-defined functionalized polystyrenes and poly(methyl methacrylate)s with 1,3-butadienyl groups has been described by the methodology based on the functionalization reactions of living anionic polymers of a new substituted 1,1-diphenylethylene with a 1,3-butadienyl group, 1-[4-(4-methylene-5-hexenyl)phenyl]-1-phenylethylene (1). Both chain-end and in-chain functionalized polystyrenes with one or two 1,3-butadienyl groups were synthesized by utilizing the addition reactions of living polystyrenes to 1 followed by methanol termination or treatment with appropriate electrophiles. On the other hand, chain-end and in-chain functionalized poly(methyl methacrylate)s with one or two 1,3-butadienyl groups were obtained by the living anionic polymerization of methyl methacrylate with the adduct prepared from 1 and either s-BuLi or lithium naphthalenide. The 1,3-buadienyl groups thus introduced were quantitatively transformed into anhydride or epoxy functions without any side reactions by the (C2H5)2AlCl-catalyzed Diels-Alder reaction or by treatment with 3-chloroperoxybenzoic acid.