Elastoviscous properties of polyisobutylene. V. The transition region

Abstract

Abstract A discussion of the principles for the extension of the time scale for elastoviscous data by use of experimental information obtained at various temperatures is presented. A quantity k is defined such that stress relaxation curves at all temperatures are identical if plotted versus time divided by k(T) . This function k(T) is compared with the function a(T) used by Ferry and by Fox and Flory for other viscoelastic data. In particular, k(T) for polyisobutylene is found to be identical (within experimental error) with a(T) obtained by Fox and Flory from viscosity measurements. The complete composite relaxation curve E r , T ( t ) for polyisobutylene is constructed from data of Brown and Tobolsky and Andrews and Tobolsky. E r , T ( t ) is shown to have three regions: a “rubbery region,” and a “glassy region.” This conclusion is reinforced by comparison with data on polymethylmethacrylate. The “rubbery region” is molecular weight dependent, whereas the “transition region” is molecular weight independent and independent of the presence of a small concentration of cross links. Simple empirical functions are given for E r , T ( t ) and the corresponding distributions of relaxation times are also presented.