Effects of synthesis-solvent composition and initiator concentration on the swelling behaviour of poly(N-isopropylacrylamide) P(NIPAAM), poly(NIPAAM-co-dimethyl itaconate), and poly(NIPAAM-co itaconic acid) gels

The effects of synthesis-solvent composition, initiator concentration, comonomer type and monomer purity on the volume swelling ratios, and polymer-solvent interaction parameter X have been investigated as a function of temperature. Non-ionic N-isopropylacrylamide (NIPAAM) homopolymer gels, poly[NIPAAM-co-(dimethyl itaconate)] (P(NIPAAM-co-DMI)) and poly[NIPAAM-co-(itaconic acid)] (P(NIPAAM-co-IA)) gels containing hydrophobic (DMI) and hydrophilic (IA) comonomers were prepared by free radical polymerization using potassium persulfate (KPS) -N, N, N′, N′-tetramethyl ethylene diamine (TEMED) (redox initiator) in the presence of an N, N′-methylene bis(acrylamide) (MBAAM) cross-linking agent. The synthesis-solvent composition (40/60 mixture of water/methanol and water) and initiator concentration employed significantly affected the properties of the NIPAAM gels. The transition temperatures of P(NIPAAM-co-IA) gels synthesized in water/ methanol mixture were higher than that of the gel obtained in water. Furthermore, X values of the NIPAAM homopolymer gel prepared with higher KPS content was an increasing function of temperature, while X values of the sample obtained with lower initiator concentration changed around a critical solubility value 0.50. The results obtained also show that the interactions between monomer and solvent molecules in the reaction media (ie composition of the pregel solution) have an important effect on the formation and properties of the network structure (ie pore sizes of the gels).