Diffusion of Polymer in Binary and Ternary Semidilute Solutions

Abstract

Dynamic properties of PS/TOL, PS1/PS2/TOL and PS1/PMMA2/TOL semidilute solutions (in which PS, PMMA and TOL denote polystyrene, poly(methyl methacrylate), and toluene, respectively; “1” denotes the matrix polymer and “2”, the probe polymer) have been studied systematically by using dynamic light scattering. Unimodal characteristic linewidth distribution was observed for two narrow PS/TOL binary solutions consisting of high molecular weight and narrow molecular weight distribution (MWD) polystyrenes with M w = 8.6 x 106, M w /M n ≤ 1.17, and M w = 10 x 106, M w /M n ≤ 1.20. But two modes in the characteristic linewidth distribution appeared in a polydisperse PS/TOL binary solution with M w = 23 x 106, M w /M n ~ 2.0, which indicated that polydispersity could lead to the observed bimodal behavior in the characteristic linewidth distribution even at small scattering angles where KR g < 1, with K and R g being the scattering vector and the root-mean-square z-average radius of gyration. Two modes also existed in a ternary solution composed of a high molecular weight component PS (M w = 8.6 x 106, M w /M n ≤ 1.17) and a low MW component PS (M w - 2.3 x 105, M w /M n ~ 1.06). This observation agreed with the theory on ternary mixtures proposed recently by Benoit and his coworkers, and confirmed the effect of polydispersity on dynamic behavior of semidilute polymer solutions. The fast mode was interpreted as the cooperative diffusion of entangled chains and the slow mode could be attributed to the coupling of the matrix polymer with the probe polymer. This coupling was further ascertained by the bimodal behavior in two PS1/PMMA2/TOL ternary solutions, in which the probe polymer PMMA was isorefractive with the solvent TOL. The effect of star configuration and the extent of entanglements in two PS1/PS2/TOL ternary solutions with 4-arm and 12-arm star PS as probe polymers have also been examined.