Influence of reaction conditions on the synthesis of self-cross-linked N-isopropylacrylamide microgels

We report systematic investigations of the reaction conditions necessary for the production of self-cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgel particles. Reaction temperatures (T-syn) ranging from 40 to 90 degreesC and various monomer (C-NIPAM) and initiator (C-KPS) concentrations were investigated. Laser light scattering was used to characterize the resultant gel particles at 25 and 40 degreesC, below and above the phase transition temperature of PNIPAM. By comparing the molar masses measured at these two temperatures, well-defined ranges of T-syn, C-NIPAM, and C-KPS were found in which the polymer chains were well self-cross-linked and formed gel networks. Variations in the size and solid density as a function of these parameters are also discussed.