TEMPERATURE- AND SOLVENT-INDUCED CONFORMATIONAL TRANSITIONS OF STEREOREGULAR POLY(METHYL METHACRYLATE) BY FTIR, FT-NMR, AND SMALL ANGLE X-RAY SCATTERING (POLYMETHYL)

Vinyl polymers, in general, behave according to randomly coiled chains in solution, but PMMA in the syndiotactic configuration is known as the only synthetic polymer to exhibit a pronounced deviation from the random coil, which has been investigated by small angle X-ray scattering (SAXS). On the other hand, PMMA in the isotactic configuration is believed to be closer to randomly coiled chain.; In this work, elucidation of conformations of stereoregular PMMA in solution was attempted by examining possible conformational transitions, which could be induced either by temperature or solvating power of solvents. The conformational transitions are expected to be very small to be detected and to occur in different levels of scale: long-range main chain transition, rotation of the side group as a whole about the C-C bond which links it to the main chain, and internal rotation of the side group.; Fourier transform IR and NMR (FT-IR and FT-NMR) were employed to investigate the short-range conformational transitions in addition to SAXS method, which can be best used for studying the long-range conformational transitions. These three techniques supplement with each other in a valuable way. Thermodynamically contrasting polymer-solvent systems were employed. Temperature was varied from room temperature to 70(DEGREES)C in most cases depending on solvent used.; Transitional changes in the chemical-shifts and the integrated intensity of NMR signals, absorbances of IR peaks in the range 1500-1300 cm('-1), and the polymer solution parameters such as hydrodynamic radius of gyration and the persistence length obtained from SAXS data were observed and the results are coherent.; A tentative explanation for the transitions observed is given: transitions between two helices in the case of isotactic PMMA; helix to random coil transition for syndiotactic PMMA. The proposal made in this study would be the first indication that a nonbiological polymer could exhibit helix-random coil transition. The well-known (beta)-transition of PMMA in the bulk is discussed based on the IR transition of syndiotactic PMMA observed in both bulk and solution phase at a temperature corresponding to the (beta)-transition.