The molecular weights of poly(N-vinylform-amide) [poly(NVF)] obtained by free-radical polymerization were expanded from being in the range of thousands to hundreds of thousands. Primary amino groups were introduced by the hydrolysis of poly(NVF) under both acidic and basic conditions. After 2 h polyvinylamine [poly(VAm)] was given at 60degreesC under a 2N NaOH solution. The apparent activation energy of poly(NVF) hydrolysis was 61.8 kj/mol. Furthermore, alkyl side chains were partly introduced by a polymer modification reaction in poly(VAm) with carboxylic acid, using WSC (water-soluble carbodiimide) as the activating agent to produce the stimuli-responsive poly(VAm) derivative. The effects of external stimuli such as temperature and pH on the phase-transition behavior of the copolymers were then studied. The lower critical solution temperature at pH 12 decreased depending on the alkyl group content. The phase-transition behavior of the resulting polymers was also found to vary depending on the side-chain length of the alkyl groups. (C) 2003 Wiley Periodicals, Inc.