A novel reactive polymer containing cyanate groups in the side chain was prepared by free radical polymerization of a cyanate-containing monomer, 2-(4-cyanatophenyl)ethyl methacrylate (1). The monomer 1 and its polymer, poly[2-(4-cyanatophenyl)ethyl methacrylate] (PCPMA), were stable under the air for a long period. The copolymerization of 1 and methyl methacrylate provided the corresponding copolymers with various cyanate contents. The availability of the cyanate-containing polymers as a reactive polymer was investigated. Model reaction using 4-cyanatotoluene revealed that a cyanate group reacted with aliphatic amines, whereas no reaction occurred in the presence of water, alcohols, and aromatic amines under mild conditions. Post-functionalization of PCPMA was demonstrated using aliphatic amines or diamines. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 699-706