The Effects of Molecular Orientation on the Physical Aging and Mobility of Polycarbonate-Solid State NMR and Dynamic Mechanical Analysis

摘要

Solid-state NMR and dynamic mechanical (DMA) measurements were per- formed on a series of uniaxially hot-drawn bisphenol-A polycarbonate samples in order to determine the effects of stretching on the structure, mobility, and local orientation envi- ronment. Proton spin-lattice relaxation times, ~1H T_(1p), for the phenylene carbon protons were fitted to a biexponential decay function, and both the long and short relaxation times initially increased with stretching. Intensity data indicated an increase in the number of short relaxation time protons and a decrease in the number of long relaxation protons with orientation. Similarly, DMA spectra showed that the #beta#-relaxation strength also increased with drawing, which implied an increase in the number of localized segmental relaxations. It is theorized that the long and short ~1H T_(1p) relate to protons within tightly packed "cooperative domains," and to those with greater localized free-volume, respectively. Stretching is known to distort the free-volume distribution, causing a decrease in the mean free-volume but an increase in the number oflarger, more elliptical holes. This is expected to cause a decrease in the a-transition mobility (due to larger cooperative domains) and an increase in the (3-mobility (due to the increase in the number of (3-relaxing segments associated with the larger free-volume holes). These predictions are consistent with results recently reported by Shelby and Wilkes on the physical aging and creep behavior of these samples (M. D. Shelby & G. L. Wilkes, Polymer 1998, 39, 6767; M. D. Shelby & G. L. Wilkes, J Polym Sci Part B: Polym Phys 1998, 36, 2111).