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

Abstract

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.