Structural Analysis of Crosslinking Junctions of Vulcanized Natural Rubber

Abstract

Synopsis: Crosslinking junctions are well-known to be one of the important factors governing mechanical properties of vulcanized rubbers. It is, therefore, necessary to develop a positive method to analyze the crosslinking junctions through solid state NMR spectroscopy, since the vulcanized rubbers are insoluble in most deuteriated solvents. Here, outcomes in the last three-decades were summarized for study on the structural analysis of the crosslinking junctions of vulcanized natural rubber, which was performed by solid state NMR spectroscopy. First, assignments of some signals in ¹³C-NMR spectrum for vulcanized natural rubber were described in conjunction with values of chemical shift estimated for plausible crosslinking junctions by empirical method. Problems on the assignments were explained with respect to the vulcanization mechanism. Secondly, the positive structural analysis of the crosslinking junctions of the vulcanized natural rubber are described with field gradient fast magic angle solid state NMR spectroscopy, which was developed by a novel innovative technology. Finally, relationship between the assigned signals and mechanical properties were discussed in regard to newly proposed vulcanization mechanism.