SPIN RELAXATION AND LOCAL MOTION IN DISSOLVED POLYCARBONATE

Carbon-13 and field-dependent proton spin-lattice relaxation times were measured as a function of temperature and molecular weight for 10 wt % solutions of polycarbonate in CDCl3. The spin-lattice relaxation times are interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer, phenyl group rotation, and methyl group rotation. Correlation times for all of the three local motions are very similar, from -10 to +60 °C, leading to the conclusion that these three local motions are coupled or synchronous. Correlation times range from about 0.35 ns at -10 °C to 0.05 ns at +60 °C. The temperature dependences of the motions differ slightly with phenyl group rotation, having the lowest apparent activation energy of 13 kJ. This low value is reasonable in view of a semiempirical calculation by Tonelli, and the apparent activation energies of segmental motion and methyl group rotation have more typical values of 19 and 22 kJ, respectively. Facile phenyl group rotation occurs in another engineering plastic, poly(2, 6-dimethyl-1, 4-phenylene oxide), but in this latter polymer the phenyl group rotation is not close in time scale to the other motions. © 1979, American Chemical Society. All rights reserved.