一种四臂聚苯乙烯凝胶的激光光散射研究

采用原子转移自由基方法(ATRP)合成窄分布的末端基为巯基的四臂星型聚苯乙烯(4-PS-SH).巯基容易被空气中的氧气氧化生成二硫键,会引起四臂星型聚苯乙烯分子间交联.利用激光光散射研究了四臂聚苯乙烯在亚浓溶液中氧化交联生成大的胶束进而生成宏观化学凝胶的过程.静态激光光散射测量结果表明四臂聚苯乙烯亚浓溶液以及凝胶样品的时间平均散射光强不随测量位置的变化而涨落,说明此凝胶是结构均一的化学凝胶.动态光散射结果表明在四臂聚苯乙烯亚浓溶液氧化生成凝胶的过程中,动态强度-强度时间相关函数的慢运动衰减的贡献最初随着氧化时间的增加逐渐增强,当氧化反应进行到一定程度时慢运动的贡献又逐渐减弱,最终慢运动消失.生成的化学凝胶的相关函数与最初亚浓溶液的相关函数几乎重合.静态和动态激光光散射结果表明生成的四臂聚苯乙烯凝胶是结构均匀的化学凝胶.

STUDIES ON A FOUR-ARM POLYSTYRENE GEL BY LASER LIGHT SCATTERING

Atom transfer radical polymerization(ATRP)was used to synthesize narrowly distributed 4-arm-polystyrene star chains(4-PS-Br).Then the bromine end functional groups were further modified to thiol groups(4-PS-SH).Oxidization of each two thiol end groups leads to a disulfide bond(—S—S—),which enables us to slowly crosslink the PS star chains in THF solutions to form polymer clusters,then gels.Static laser light scattering(SLS)shows that in both semidilute solutions and gels the time-average scattered intensity changes little with the sample position,where the sample position is arbitrarily chosen by rotating and lifting the sample cuvette,indicating this chemical gel is homogeneous and speckle-free.Dynamic laser light scattering(DLS)shows that first there is only one fast decay mode of the time-time intensity correlation function in the original semidilute solution.Then the slow modes of the correlation function appear and the contributions of the slow modes increase at the early oxidation stage,indicating the formation of large cross-linked clusters.With oxidation time increase the contribution of the slow mode decreases,finally disappears.The correlation functions of the chemical gel are nearly the same as those of the original semidilute solution.The normalized intermediate scattering function can fully relax to zero,indicating that the gel has no frozen-in static component,and the speckles of other polymer gels originate from large voids inside,not cross-linked chains(clusters).Both SLS and DLS results indicate that this polystyrene gel is a homogeneous chemical gel.