Range Of Reduced Frequencies Research Articles

Some dynamic mechanical properties of polyisobutylene over a wide temperature range

A cantilever resonance method has been used to measure the complex Young's modulus of polyisobutylene from 90 to 560° K at a number of points in the frequency range 30-300 c/s. Using the method of reduced variables, the results have been expressed as a function of frequency at constant temperature and compared with other published data on this material over comparable reduced frequency ranges. Agreement is quite good over a limited reduced frequency range, but the present results predict a higher value for the real part of the modulus at infinitely high frequencies, and show the small dispersion peak in the imaginary modulus curve displaced to a higher reduced frequency. The validity of extrapolating the frequency shift factor to high and low temperatures is questioned, and suggested as a possible explanation for the discrepancies. A comparatively large value of the temperature coefficient of the modulus at 90° K suggests that an appreciable configurational entropy term is still contributing to the free energy of the polymer at these low temperatures.