聚(N-异丙基丙烯酰胺)水凝胶微球体积相变的研究

窄分散的聚（Ｎ 异丙基丙烯酰胺）水凝胶微球用乳液聚合方法制备，并用动态和静态光散射对其体积相变进行了研究．与水中聚（Ｎ 异丙基丙烯酰胺）线性单链比较，水中凝胶微球的体积相变温度较高，对温度的响应比较平缓．相变是连续的，有别于大块凝胶非连续的体积变化．在体积相变过程中，凝胶微球始终是密度均一的热力学稳定球体．从相变过程网络密度的变化可以确定，绝大部分的水在收缩过程被排了出来，但在紧缩的凝胶微球中仍含有约７０％的水．

STUDY OF THE PHASE TRANSITION OF POLY (N ISOPROPYLA CRYLAMIDE) SPHERICAL MICROGEL IN WATER

Narrowly distributed spherical microgel particles of poly(N isopropylacrylamide) (PNIPAM) were prepared by emulsion polymerization in water.The volume phase transition of the microgel particles was studied by static and dynamic laser light scattering.The results were compared with the coil to globule transition of individual long linear PNIPAM chains.The microgel particles have a higher transition temperature,but a less sharp phase transition in comparison with that of long linear chains.This difference has been attributed to both the short length and the broad length distribution of the subchains inside the microgels.A combination of static and dynamic laser light scattering results revealed that even in a highly collapsed state the microgel particles retained ～70% of water and the density of the microgel networks increased from 0 021 g/ml to ～0 3 g/ml during the phase transition.The phase transition of the microgel particles is continuous,in contrast to the discontinuous volume phase transition in bulk PNIPAM gels.The microgel particles are thermodynamically stable even at their collapsing limit.The behavior of microgel particles is compared with that of individual PNIPAM chains.