Solid-state exchange NMR characterization of segmental dynamics in glassy poly(alkyl methacrylate)s

Slow side-group and main-chain P-relaxation dynamics in a series of glassy poly(alkyl methacrylate)s (PRMAs) with varying side-group sizes were studied by one-dimensional (1-D) centerband-only detection of exchange (CODEX) and static pure-exchange (PUREX) nuclear magnetic resonance (NMR) techniques. The (COO)-C-13 signal in 1-D PUREX experiments was analyzed to characterize the flips and small-angle motions of the side groups quantitatively. By comparing the (COO)-C-13 exchange intensities obtained from 1-D PUREX and CODEX experiments, it A-as possible to show that the small-angle reorientations vary between backbone segments. Analysis of the backbone (CH)-C-13, CODEX data supplied direct and quantitative information about the amplitudes of the main-chain motion, which is also reflected in the side-group reorientation due to the coupling between side group and backbone. The data obtained from both NMR exchange techniques were correlated, providing. an accurate, consistent description of the backbone and side-group motion The effects of side-a-roup size and temperature on the fraction of flipping side groups were studied systematically by 1-D PUREX NMR. The flipping fraction at ambient temperature decreases with increasing the side-group size. It increases gradually with temperature for two PRMAs with conformationally flexible side groups. while it is constant over wide temperature ranges for poly(methyl metbacrylate) and poly(cyclohexyl methacrylate).