ETHYLENE-PROPYLENE COPOLYMER AGGREGATION IN SELECTIVE HYDROCARBON SOLVENTS

Intrinsic viscosity measurements of 80-20 molar ratio ethylene-propyle ne (EP) copolymers in selective solvents have shown a dramatic decreas e in viscosity when temperature was lowered from 50 to -10-degrees-C. In this study we show that both chain association and cluster contract ion can occur. Viscometry, dynamic light scattering (DLS), and static light scattering (SLS), including Zimm plots, were used to examine the number of polymer chains in the aggregated clusters and the cluster s ize of a 322 000 molecular weight EP copolymer in methylcyclohexane (M CH) and tetralin (THN). For all temperatures and concentrations studie d the polymer formed aggregated clusters. However, in MCH (the better solvent) the polymer volume fraction, from viscometry, maintained a co nstant value over temperature whereas in THN (the poorer solvent) the polymer volume fraction dropped by a factor of 5 as the temperature wa s lowered to -10-degrees-C. Thus, while both systems formed aggregated clusters, the solvent quality determined the microstructure which cau sed this temperature-sensitive viscosity behavior. Although all data s howed polymer aggregation, higher values were obtained for the average number of chains in the clusters by a combination of viscometry and D LS than by SLS.