DISTINCTIVE MANIFESTATIONS OF SEGMENTAL MOTION IN AMORPHOUS POLY(TETRAHYDROFURAN) AND POLYISOBUTYLENE

Polyisobutylene (PIB) and poly(tetrahydrofuran) (PTHF) exhibit segmental relaxation behavior that is distinctly different from that found for other amorphous polymers. These unusual properties include a segmental relaxation dispersion that is much broader when measured mechanically than as seen by other spectroscopic techniques, a relative insensitivity of the segmental relaxation time to temperature, a small ''steepness index'', and an absence of encroachment of the segmental modes in time scale toward the Rouse region as temperature is lowered. It is proposed herein that these phenomena are the result of the very low extent to which segmental relaxation in PIB and PTHF is constrained by nonbonded neighboring segments. This weak intermolecular coupling, deduced from quasi-elastic neutron scattering measurements, solid-state NMR spectroscopy, and the temperature dependence of the segmental relaxation time, arises from the smooth, symmetric, and flexible structure of the two polymers.