A study of solvent motion in acetone-PMMA solutions using ¹³C and ¹H spin-lattice relaxation measurements

The ¹³C and ¹H spin-lattice relaxation times of acetone in solutions containing from 0 to 20% poly(methyl methacrylate) have been measured from -55°C to 120°C. The ¹³C measurements show that except at low temperature and the higher polymer concentrations, solvent rotation is little affected by the presence of polymer molecules. By assuming that the ¹³C relaxation time is entirely intramolecular in origin, and by progressive deuteration of the acetone, the ¹H relaxation time has been separated into intramolecular, acetone-acetone intermolecular and acetone-polymer intramolecular contributions. These results show that up to 10% of polymer or so does not affect solvent diffusion, but for 20% polymer, solvent diffusion is perceptibly slowed down, and the activation energy increased by 50%. The data give no indication of polymer conformational transitions in this temperature range, as suggested by others elsewhere, but this may be because of the very short-range sensitivity of n.m.r. measurements.