Effects of the reaction parameters on the properties of thermosensitive poly(N-isopropylacrylamide) microspheres prepared by precipitation and dispersion polymerization

Poly(N-isopropylacrylamide) (PNIPAAm)-based microspheres were prepared by precipitation and dispersion polymerization. The effects of several reaction parameters, such as the type and concentration of the crosslinker (N,N'-methylene-bisacrylamide or ethylene dimethacrylate), medium polarity, concentration of the monomer and initiator, and polymerization temperature, on the properties were examined. The hydrogel microspheres were characterized in terms of their chemical structure, size and size distribution, and morphological and temperature-induced swelling properties. A decrease in the particle size was observed with increasing polarity of the reaction medium or increasing concentration of poly(N-vinylpyrrolidone) as a stabilizer in the dispersion polymerization. The higher the content was of the crosslinking agent, the lower the swelling ratio was. Too much crosslinker gave unstable dispersions. Although the solvency of the precipitation polymerization mixture controlled the PNIPAAm microsphere size in the range of 0.2-1 mu m, a micrometer range was obtained in the Shellvis 50 and Kraton G 1650 stabilized dispersion polymerizations of N-isopropylacrylamide in toluene/heptane. Typically, the particles had fairly narrow size distributions. Copolymerization with the functional glycidyl methacrylate monomer afforded microspheres with reactive oxirane groups. (c) 2005 Wiley Periodicals, Inc.