The Dynamic Bulk Viscosity of Polyisobutylene

Abstract
The dynamic bulk modulus of a high molecular weight polyisobutylene is calculated from measured longitudinal‐wave and shear moduli. A viscous or energy‐dissipating process associated with pure volume deformation is found, which appears to be a relaxation process. The peak in absorption of the shear and bulk moduli and the apparent activation energies associated with the two types of deformation are at least approximately the same, suggesting that the fundamental molecular mechanism involved in the two types of deformation may be the same.