ISSN:
0887-6266
Keywords:
orientation
;
physical aging
;
free volume
;
glass-transition
;
dilatometry atactic-polystyrene
;
bisphenol A polycarbonate
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
It has recently been demonstrated that hot-drawn samples of bisphenol A polycarbonate (PC) have a 50% higher volume relaxation rate than their isotropic counterpart even though the oriented samples have a lower initial free volume (i.e., higher density).1 In an attempt to better understand this paradox, samples of unaged, hot-drawn PC were characterized thermodynamically and kinetically as a function of orientation. Heat capacity, hole energy, and Tg data indicate that the chain mobility is actually decreasing slightly with orientation, possibly due to the hindered motion brought about by tighter packing, stronger intermolecular bonding, and reduced free volume. Nonetheless, this decrease in localized mobility is in contradiction to the enhanced volume relaxation rates observed for the oriented samples. In contrast, dynamic mechanical data indicate an increase in the relaxation strength of the β-transition (-100°C at 1 Hz) upon stretching for both the stretch and transverse directions. This implies that more segments are actively participating in the relaxation process for the oriented samples even though their individual localized mobility might be slightly lower. The net result is an increase in “effective” mobility for the oriented samples. It is conjectured that the enhanced relaxation strength of the oriented samples is a result of the stretching process somehow activating more of the chains into a higher energy state, and may be related to the physical aging concept of stress-induced rejuvenation/acceleration. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2111-2128, 1998
Additional Material:
15 Ill.
Type of Medium:
Electronic Resource
