Characterization of poly(N,N-diethylacrylamide) and cloud points in its aqueous solutions

Abstract

The mean-square radius of gyration, second virial coefficient and intrinsic viscosity were determined in methanol at 25.0 °C for two types of poly(N,N-diethylacrylamide) (PDEA) samples that were synthesized by radical polymerization in tert-butanol and benzene using azobis(isobutyronitrile) as an initiator. Analyses of these results indicated that the primary structure of both PDEA samples was linear. The cloud points of the two PDEA samples were also determined in aqueous solutions. For the two types of PDEA samples, the cloud point decreased as the weight-average molecular weight Mw of the sample increased, which is in contrast to previously reported results for poly(N-isopropylacrylamide) (PNIPA) samples, even though those samples have the same hydrophobic chain-end groups. In addition, the cloud-point curve of each PDEA sample has a critical point, which has not been previously reported for PNIPA. The critical point shifted to the upper right with decreasing Mw, as predicted by conventional polymer solution thermodynamics. Therefore, the aqueous PDEA solutions exhibited typical phase behavior that is consistent with the lower critical solution temperature type, which is substantially different from that observed for aqueous PNIPA solutions. The cloud point was determined in aqueous poly(N,N-diethylacrylamide) (PDEA) solutions. It was found that the cloud-point curve of each PDEA sample has a critical point and each PDEA solution exhibits phase separation into two liquid phases when the temperature is increased above its cloud point, which has not been previously observed for aqueous poly(N-isopropylacrylamide) (PNIPA) solutions. Therefore, the aqueous PDEA solutions exhibit typical phase behavior of lower critical solution temperature type, which is substantially different from that observed for PNIPA.