SIDE-CHAIN STRUCTURE OF POLY(METHACRYLIC ACID) AND ITS ZINC SALTS IN THE SOLID-STATE AS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NMR-SPECTROSCOPY

High-resolution solid-state C-13 CP/MAS NMR experiments for isotactic and syndiotactic poly(methacrylic acid)s (PMAA) have been carried out at room temperature, and further those for the zinc salts have been carried out at temperatures from room temperature to about 170-degrees-C. The carboxyl carbon resonance of PMAA was separated into four peaks, three of which move about 3, 6 and 9 ppm downfield, respectively, as compared with the corresponding chemical shift values in solution. The chemical shift value of the remaining peak agrees with that in solution. Based on these experimental results and quantum chemical calculations on the C-13 NMR chemical shift, the observed large downfield shift in the solid state is ascribed to the formation of intermolecular or intramolecular hydrogen bonds. Both the C-13 chemical shift values and the relative peak intensities of the carboxyl carbon in PMAA-zinc salt were almost independent of temperature at temperatures from room temperature to 170-degrees-C. This suggests that the interaction between carboxyl group and zinc does not change within its temperature range.