Synthesis and phase behavior of aqueous poly(N-isopropylacrylamide-co-acrylamide), poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and poly (N-isopropylacrylamide-co-2-hydroxyethyl methacrylate)

Poly(N-isopropylacrylamide) (PNIPAM) and random copolymers of Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNIPAM-HEMA), poly (N-isopropylacrylamide-co-acryl-amide) (PNIPAM-AAm), and poly (N-isopropylacrylamide-co-N,N-di-methylacrylamide) (PNIPAM-DMAA) with various volume fractions gamma of NIPAM were synthesized by radical polymerization. The phase behavior of the polymers in water was investigated by means of optical transmittance and dynamic light scattering. With decreasing gamma, the cloud point temperature T-cp for PNIPAM-HEMA decreased whereas the T-cp for both PNIPAM-AAm and PNIPAM-DMAA increased. Increase of hydrodynamic radius around T-cp, which resulted from the aggregation of the globules of each polymer, was observed from dynamic light scattering. The relationships between the reciprocal of T-cp of the polymer solutions and 1-gamma were linear for the three copolymers in the experimental range of 0.65 < 1. The results are discussed from the aspect of the interaction parameters of copolymer solutions.