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 80/20 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.