Intrinsic viscosity measurements of 80-20 molar ratio ethylene-propylene (EP) copolymers in selective solvents have shown a dramatic decrease in viscosity when temperature was lowered from 50 to -10 °C. In this study we show that both chain association and cluster contraction 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 size of a 322 000 molecular weight EP copolymer in methylcyclohexane (MCH) and tetralin (THN). For all temperatures and concentrations studied the polymer formed aggregated clusters. However, in MCH (the better solvent) the polymer volume fraction, from viscometry, maintained a constant value over temperature whereas in THN (the poorer solvent) the polymer volume fraction dropped by a factor of 5 as the temperature was lowered to -10 °C. Thus, while both systems formed aggregated clusters, the solvent quality determined the microstructure which caused this temperature-sensitive viscosity behavior. Although all data showed polymer aggregation, higher values were obtained for the average number of chains in the clusters by a combination of viscometry and DLS than by SLS.

Static light scattering measurements of ethylene-propylene random copolymer revealed that solvophobic ethylene segments were responsible for both aggregation and cluster density variations over temperature. By changing the molar ratio of ethylene to propylene, as well as the solvent, we controlled the degree of solvophobicity. This caused markedly different combinations of aggregation and density variations with temperature. Combinations observed from 50 to -10°C included: a) constant aggregation and density for an E/P ratio of 60/40 in methylcyclohexane, b) increased aggregation at -10°C combined with a constant cluster density for an E/P ratio of 60/40 in tetralin and an E/P ratio of 80/2O in methylcyclohexane, c) increased aggregation and density at -10°C for an E/P ratio of 80/20 in tetralin. We also show how these combined microstructural changes are related to intrinsic viscosity measurements made from 50 to -10°C in these same solvents.