Multifield, temperature and concentration dependence of spin relaxation and local motion in 2,2-propane diyl-bis(4-hydroxyphenyl) polyformal

Abstract

13C and proton spin-lattice relaxation data were determined as a function of field, temperature and concentration for 2,2-propane diyl-bis(4-hydroxyphenyl) polyformal in C 2D 2Cl 4. The concentration of polymer was varied from a few per cent by weight up to the bulk rubber and temperature was varied from −20°C to +120°C. The relaxation data is interpreted in terms of several local motions including segmental motion, phenylene group rotation, methyl group rotation and formal group rotation. Segmental motion is described by a correlation function developed by Hall and Helfand which allows for cooperative and single bond transitions. The phenylene group rotation is described by the Woessner anisotropic stochastic diffusion model except at high concentration (⩾50 wt%) where the phenylene data is simulated by restricted rotation. Methyl group rotation is described by the Woessner three fold jump model, and the formal group rotation is described by double trans-gauche rotations about the C-O axes. At a concentration of 5 wt%, the time scale of segmental motion is slightly slower than in bisphenol-A-polycarbonate. However, the time scales of phenylene group and methyl group rotations are nearly identical for both polymers. A comparison is also made with chloral polyformal, another similar polyformal. The effect of concentration on local motion was monitored by 13C spin-lattice relaxation measurements at three Larmor frequencies over the range of 5 to 100 wt% polymer at a temperature 40°C above the glass transition of this polyformal. The rate of local chain motion decreases as the concentration of polymer increases with the exception of methyl group rotation which remains constant. The correlation times for several local backbone motions are fit to free volume theory which yields a fractional free volume of 0.38 for the solvent (C 2D 2Cl 4) and 0.28 for the polymer.