DISTRIBUTIONS OF CORRELATION TIMES AND C-13 NUCLEAR MAGNETIC-RESONANCE SPECTRA OF POLYMERS

Carbon-13 spin-lattice relaxation times, line widths, and nuclear Overhauser enhancement factors have been measured at 22.6 MHz and 35° for a solution of isotactic polystyrene, solid cis-polyisoprene, and solid cis-polybutadiene. The data are interpreted in terms of a broad asymmetric distribution of correlation times. A log-1 2 density function is used to describe the distribution, and a rationale is presented for its use. The width of the distribution can be related to the number of degrees of freedom involved in the main-chain segmental motion, and hence is suggested to be a relative measure of the extent of cooperative segmental motion. Of the three polymer systems considered, cooperative motions, at 35°, are the most pronounced in cis-polybutadiene. © 1973 American Chemical Society. All rights reserved.