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, como nomer type and monomer purity on the volume swelling ratios, and polymer-so lvent interaction parameter chi have been investigated as a function of tem perature. Non-ionic N-isopropylacrylamide (NIPAAM) homopolymer gels, poly[N IPAAM-co-(dimethyl itaconate)] (P(NIPAAM-co-DIMI)) and poly[NIPAAM-co-(itac onic acid)] (P(NIPAAM-co-IA)) gels containing hydrophobic (DMI) and hydroph ilic (IA) comonomers were prepared by free radical polymerization using pot assium persulfate (KPS)-N, N, N', N'-tetramethyl ethylene diamine (TEMED) ( redox initiator) in the presence of an N, N'-methylene bis(acrylamide) (MBA AM) cross-linking agent. The synthesis-solvent composition (40/60 mixture o f water/methanol and water) and initiator concentration employed significan tly 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, chi values of the NIPA AM homopolymer gel prepared with higher KPS content was an increasing funct ion of temperature, while chi values of the sample obtained with lower init iator concentration changed around a critical solubility value 0.50. The re sults obtained also show that the interactions between monomer and solvent molecules in the reaction media tie composition of the pregel solution) hav e an important effect on the formation and properties of the network struct ure tie pore sizes of the gels). (C) 2000 Society of Chemical Industry.