DYNAMICS OF MACROMOLECULAR CHAINS .6. CARBON 13 AND PROTON NUCLEAR MAGNETIC-RELAXATION OF POLYSTYRENE IN SOLUTION

SPin-lattice **1H and **1**3C nuclear magnetic relaxation (NMR) times T//1 have been measured for solutions of polystyrene in hexachlorobutadiene at two different frequencies. Some nuclear Overhauser enhancements and linewidths have also been determined. At 15 and 25 MHz the relaxation times T//1 of the ortho and meta carbons show two different dependences on temperature. These measurements indicate internal motion of phenyl groups around the C// alpha - C//p//a//r//a axis. A single isotropic correlation time is inadequate to explain the relaxation data for the para carbon. Use of a diamond-lattice motional model reveals that segmental reorientation of the chain backbone of polystyrene can be described in terms of two correlation times, rho characterizing the three-bond motion process, and THETA reflecting either isotropic motions of subchains or departure from an ideal lattice. Data on low-molecular-weight polystyrene indicate the participation of overall rotatory diffusion in the relaxation processes. This motion is no longer efficient in high-molecular-weight polymers, where relaxation is due to segmental reorientation.