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 (Tsyn) ranging from 40 to 90 °C and various monomer (CNIPAM) and initiator (CKPS) concentrations were investigated. Laser light scattering was used to characterize the resultant gel particles at 25 and 40 °C, below and above the phase transition temperature of PNIPAM. By comparing the molar masses measured at these two temperatures, well-defined ranges of Tsyn, CNIPAM, and CKPS 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.