Long chain monomers such as hexanediol diacrylate (HDDA) trailed in canals various monomers of relatively large size to form urea canal complexes. The relationship between the monomer composition and copolymer composition after in-source copolymerization and post-copolymerization of irradiated HDDA and the second monomers (styrene and methacrylonitrile) in urea canal was investigated. With in-source copolymerization at 25°C, the content of the second components in the polymer was far larger than that in the monomer feed, while, in post-copolymerization at elevated temperatures, the ratio of the two components in the polymer nearly agreed with their ratio in the monomer mixture.