Chain Diffusion of Polystyrene in CS₂

Since Wellinghoff et al.1 found that atactic polystyrene can form a thermally reversible gel in various solvents, several further investigations have ensued to understand the nature of the physical gelation. Tan et al.2 and Boyer et al. proposed that chain overlap is responsible for the gelation, whereas Gan et al. suggested the formation of microcrystal in the gel state to explain their observation of the enhanced low-angle light scattering in the gel state. From calorimetry measurement, the concentration of the physical cross-links in the gel structure was estimated to be 5-10% by Frangois et al. Despite these efforts, the chain configuration in the gel state is not fully understood, and it demands further examination. In this experiment, the forced Rayleigh scattering (FRS) technique was used to study the translational diffusion of the individual polymer chains in the gel state. Our previous experiment on gelatin showed that self-diffusion is quenched below the gel point. Whether chain diffusion is also quenched in polystyrene/CS2 gel is a burning question. This paper is focused on the issue of self-diffusion of polystyrene chains in CS2 above and below the gelation region. By examining the self-diffusion we hope to shed some light on the nature of this gelation phenomenon.