Investigation of the effect of type and concentration of ionizable comonomer on the collapse behavior of N-isopropylacrylamide copolymer gels in water

This work was done to investigate the effect of three different ionizable c omponents (acrylic acid, AA; itaconic acid, IA; maleic acid, MA) on the vol ume phase transitions and swelling equilibria of thermoshrinking type N-iso propylacrylamide (NIPAAM) gels in water. NIPAAM copolymer gels were synthes ized by free radical crosslinking copolymerization of NIPAAM with each of A A, LA, and MA, the difference being both between configurations and carboxy l group numbers, and pK values, in the presence of N,N'-methylene-bis-acryl amide (MBAAM). The influence of comonomer concentrations (1, 5, and 10 mol %), MBAAM content (0.0096, 0.0193, and 0.0288 g), and comonomer type (AA, I A, and MA) on the external views, the percentages of equilibrium mass, and volume swellings [S %(m), 5 % (v)], the number-average molecular weight bet ween crosslinks ((M) over bar(c)), effective crosslinking densities (v,), t he change of the collapse temperatures, and swelling ratios in the swelling -shrinking process of the gels were examined. It was observed that phase tr ansition temperature and swelling degree in the case of MA having a cis con figuration and higher pK value are larger than those of the samples contain ing IA and AA. (C) 1999 John Wiley & Sons, Inc.