Gel Structures of Natural Rubber and Synthetic Isoprene Rubber

The branching degree of natural rubber (NR) estimated by GPC/LALLS measurement is higher than that of synthetic isoprene rubber (IR). Branched polymer chains and the gel networks of NR are easily decomposed by various means such as mechanical force, solvent power and enzymic deproteinization reaction. This decomposition leads to the increase of linear polymer chains. 13CNMR spectrum of the low molecular weight fraction of NR gives small signals which are characteristics of an ester group. From these facts we estimate that the NR gel consists of weak linkages such as hydrogen bonds between an ester group in NR and an amino group in protein. Since the IR gel is formed by chemical bonds, it can be randomly decomposed only by mechanical force; this results in the increase of branched polymer chains. The gel structures of NR and IR are directly observed by transmission electron microscopy. The networks of NR gel show looser than those of IR gels.