MULTIARM STAR POLYISOBUTYLENES .5. CHARACTERIZATION OF MULTIARM POLYISOBUTYLENE STARS BY VISCOMETRY, POUR POINTS, ELECTRON-MICROSCOPY, AND ULTRASONIC SHEAR DEGRADATION

Structure/property relationship of multi-arm star polyisobutylenes [- (PIB)(n)s] were characterized by a variety of techniques, including vi scometry, pour points, electron microscopy, and ultrasonic degradation . The intrinsic viscosity of -(PIB)(n)s changes very little with temp erature in the 30 to 100 degrees C range, whereas that of linear PIBs of the same molecular weight increases strongly with temperature. Kine matic viscosity measurements of select -(PIB)(n)s gave viscosity indi ces in excess of 130. The viscosity of -(PIB)(n)s is mainly determine d by the molecular weight of the arms and much less by the number of a rms or overall molecular weights. Electron microscopy of -(PIB)(n)s i ndicates a compact spherical morphology, a conclusion that was substan tiated 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.