Single and Multichain Association of Polystyrene in Solvents with Various Molecular Sizes

Abstract

The association and aggregation of polymers in the semidilute solution regime during cooling from above to below the Θ temperature were investigated by the nonradiative energy transfer (NET) and rheological method. The molecular size of the solvent was found to affect the association and aggregation behaviors of the chains. When the normal small-sized solvent, for example decalin or cyclohexane is used, the polystyrene chains first associate among each other, and form aggregates of chains with strong interchain interpenetration at the end of cooling process. However, when the solvent with larger molecular size (also called middle-sized solvent), for example dioctyl phthalate (DOP) is used, polystyrene chains contract separately and form aggregates of collapsed globules at the end of cooling process. The interpenetration between chains for the polystyrene solid sample freeze-dried from different concentrations was detected by a new strategy using dipolar filter 1H solid-state NMR under fast magic angle spinning. We found that when the small-sized solvent was used, the extent of interpenetration in the polystyrene glasses basically kept constant with the concentration of the original solution and it increased suddenly near the critical overlapping concentration ([η]c ∼ 4). However, in the case of middle-sized solvent, even up to [η]c = 10, the extent of the interpenetration kept in a very low level comparable to that from extremely dilute ([η]c ∼ 0.01) small-sized solvent solution. Such results help us to understand the behaviors of fast crystallization and relaxation dynamics of serials of polymer samples freeze-dried from middle-sized solvent solutions discovered in this laboratory.