Kinetic analysis of poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate) microgel latex formation

Curves of the conversion and particle size versus the time in the preparation of poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate) microgel latices by surfactant-free emulsion polymerization were measured. The copolymerization reactions were rapid, and their rates increased with the dimethylaminoethyl methacrylate (DMAEMA) concentration in the polymerization recipe. Particle formation occurred by a homogeneous nucleation mechanism, in which DMAEMA helped to colloidally stabilize the primary particles. In addition, a strong dependence of the water-soluble-polymer (WSP) formation on the DMAEMA concentration was found, and the DMAEMA content in the WSP was significantly higher than that in the microgel particle. A drastic variation of the crosslinking density within the microgel particle during the polymerization process was found through a comparison of the particle size determined by quasi-elastic light scattering with that determined by transmission electron microscopy. Finally, on the basis of these results, the mechanism of particle formation in this polymerization process was examined. (C) 2004 Wiley Periodicals, Inc.