Studies of hydrodynamic properties for characterizing star-shaped poly(ethylene-co-propylene)

Linear and star-shaped polyisoprene were synthesized and hydrogenated to form the targeted poly(ethylene-co-propylene) copolymers, (EP)lin and (EP)star. Hydrodynamic properties of the polymers in THF at 40 °C have been studied by gel permeation chromatography, using multiple-angle laser light scattering and differential refractive index detectors. dius of gyration Rg of (EP)star was found proportional to the molecular weight to a power of 0.34 corroborating a globular architecture and the Rg of (EP)lin to a power of 0.60 indicating a random coil conformation in a good solvent. The intrinsic viscosity [η] of (EP)lin was much higher than that of (EP)star due to the compact globular structure of star molecules. While the [η] of (EP)lin increased with an increase in the molecular weight, the molecular weight had little effect on the [η] of (EP)star as long as the arm length was fixed. Based on the measured Rg and [η], the coefficient q for the scaling law, the Mark–Houwink constant α, and the hydrodynamic radius Re have been calculated. The hydrodynamic radius Re was approximately 0.78 times of Rg for (EP)lin and was nearly identical to Rg for (EP)star. The value of Re/Rg appeared to be independent of the molecular weight for both linear and star polymers and was almost equal to those of polystyrene and polyisoprene in good solvents.