C-13 AND PROTON RELAXATION STUDY OF BACKBONE DYNAMICS OF POLY(VINYL ACETATE) IN SOLUTION

The dynamics of poly(vinyl acetate) in toluene solution has been exami ned by C-13 and proton relaxation. C-13 spin-lattice relaxation time a nd nuclear Overhauser enhancement measurements were carried out as a f unction of temperature at 50.3 and 100.6 MHz. The spin-lattice relaxat ion times for backbone protons were measured at different temperatures at 200 MHz. The relaxation data have been analyzed using the Hall-Web er-Helfand (HWH) model, which describes backbone dynamics in terms of conformational transitions and the Dejean-Laupretre-Monnerie (DLM) mod el, which includes bond librations in addition to conformational trans itions. The parameters obtained from the analysis of C-13 relaxation d ata were utilized to predict the proton relaxation data. The DLM model was found to be more successful in reproducing the experimental resul ts. To study the influence of libration further, proton relaxation dat a for poly(vinyl acetate) over a wider range of temperature reported i n the literature were analyzed by these two models. The DLM model coul d reproduce the experimental data at all temperatures whereas the HWH model was found to be successful only in accounting for the experiment al data at high temperatures. The results demonstrate the importance o f including the librational mode in the description of the backbone dy namics in polymers.