Polymerization of acrylamide in aqueous solution of poly(N-isopropylacrylamide) at lower critical solution temperature

Acrylamide (AAm) was found to polymerize in a solution of poly(N-isopropylacrylamide) (PNIPAAm) in water at around its lower critical solution temperature (LCST) (32 degrees C) without any initiators. This phenomenon was specifically observed in aqueous solutions of the polymers having LCST such as PNIPAAm and poly(methylvinylether) (PMVE). AAm polymerized only when PNIPAAm and AAm were dissolved in water below LCST of PNIPAAm and then the solution was warmed up to the polymerization temperature (40 degrees C). On the other hand, the polymerization of AAm did not proceed when AAm was added into aqueous PNIPAAm solution during and after the phase separation above 32 degrees C. Furthermore the polymerizability of AAm was remarkably affected by the concentration and molecular weight of the PNIPAAm additives. Under the condition of lower PNIPAAm concentration (0.30 mol/L), the increase in the molecular weight of PNIPAAm considerably increased the molecular weight of the resulting PAAm but decreased the yield of PAAm. Under the condition of higher PNIPAAm concentration (0.60 mol/L) the polymerizability was not so affected by the molecular weight of PNIPAAm, while the molecular weight of PAAm formed by using higher molecular weight PNIPAAm was higher than those of PAAm formed by using lower molecular weight PNIPAAm. Moreover, the molecular weight of PAAm formed by the PNIPAAm induced polymerization of AAm was much higher than that of the polymer obtained by the radical polymerization using AIBN in THF or VA- 061 in water.