Carbon-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 examined by ¹³C and proton relaxation. ¹³C spin?lattice relaxation time and nuclear Overhauser enhancement measurements were carried out as a function of temperature at 50.3 and 100.6 MHz. The spin?lattice relaxation times for backbone protons were measured at different temperatures at 200 MHz. The relaxation data have been analyzed using the Hall?Weber?Helfand (HWH) model, which describes backbone dynamics in terms of conformational transitions and the Dejean?Laupretre?Monnerie (DLM) model, which includes bond librations in addition to conformational transitions. The parameters obtained from the analysis of ¹³C relaxation data were utilized to predict the proton relaxation data. The DLM model was found to be more successful in reproducing the experimental results. To study the influence of libration further, proton relaxation data for poly(vinyl acetate) over a wider range of temperature reported in the literature were analyzed by these two models. The DLM model could reproduce the experimental data at all temperatures whereas the HWH model was found to be successful only in accounting for the experimental data at high temperatures. The results demonstrate the importance of including the librational mode in the description of the backbone dynamics in polymers.