The isochronal mechanical relaxation spectra of lightly cross-linked n
atural rubbers were measured at frequency 1 Hz. The results were analy
sed using the empirical Havriliak-Negami (HN) equation. The HN equatio
n fitted the relaxation spectra very well. The fitting parameters, alp
ha and beta, obtained from the data fitting were used to interpret the
relation between molecular motions and structure of polymers based on
the model proposed by Schonhals and Schlosser. In the high-frequency
region of relaxation spectra, the values of alpha beta were increased
with increasing sulphur content. According to the model proposed by Sc
honhals and Schlosser, it means that the molecular motions are related
to the local intramolecular interactions and are mainly influenced by
the formation of heterocyclic groups along the chain. However, in the
low-frequency region of relaxation spectra, the values of alpha were
not affected by increasing sulphur content. According to the model pro
posed by Schonhals and Schlosser, the molecular motions in this region
are related to the intermolecular interactions. They are not influenc
ed by the level of cross-linking due to the very low level of cross-li
nk. (C) 1998 Elsevier Science Ltd. All rights reserved.