Multi-arm star polyisobutylenes .5. Characterization of multi-arm polyisobutylene stars by viscometry, pour points, electron microscopy, and ultrasonic shear degradation

摘要

Structure/property relationship of multi-arm star polyisobutylenes [*-(PIB)(n)s] were characterized by a variety of techniques, including viscometry, pour points, electron microscopy, and ultrasonic degradation. The intrinsic viscosity of *-(PIB)(n)s changes very little with temperature in the 30 to 100 degrees C range, whereas that of linear PIBs of the same molecular weight increases strongly with temperature. Kinematic viscosity measurements of select *-(PIB)(n)s gave viscosity indices in excess of 130. The viscosity of *-(PIB)(n)s is mainly determined by the molecular weight of the arms and much less by the number of arms or overall molecular weights. Electron microscopy of *-(PIB)(n)s indicates a compact spherical morphology, a conclusion that was substantiated by radius of gyration measurements. Pour points of *-(PIB)(n)s are similar to -27 degrees C. Ultrasonic studies gave insight into the mechanism of shear degradation of *-(PIB)(n)s. These characteristics render *-(PIB)(n)s of interest as rheology control additives for motor oils.