The isochronal mechanical relaxation spectra of lightly cross-linked epoxidized natural rubbers (ENR) were measured at a frequency of 1 Hz and the results analyzed using the empirical Havriliak-Negami (HN) equation. The HN equation fitted the relaxation spectra very well. The fitting parameters, (Yand /3, obtained from the data fitting were used to interpret the relationship between molecular motions and structure of polymers based on the model proposed by Schonhals and Schlosser. Near the glass transition, the molecular motions of ENR in both the high and low frequency regions were not influenced by the level of cross-linking due to the low cross-linking density. Comparing with the natural rubber (NR), the epoxide groups of ENR promoted steric interactions and enhanced the inter-molecular cooperative motion. The activation energy of molecular motions for ENR was larger than observed for NR. The values of a! and o/3 of ENR were less than observed for NR. According to the model proposed by Schonhals and Schlosser, alp was correlated with the local intra-molecular motions and 01was correlated with the inter-molecular motions. The results suggest that the epoxide groups broaden the intra- and inter-molecular relaxation dispersion.
Посилання на статтю:
Dynamic mechanical relaxation of lightly cross-linked epoxidized natural rubber / W.B. Liau // Polymer. – 1999. – N 40. – P. 599–605.