Distribution ratio of carbon black in polyisobutyrene/polyisoprene rubber blends using high-resolution solid-state 13C NMR

We attempted to estimate the distribution ratio of carbon black (CB) in blends of polyisobutyrene rubber and polyisoprene rubber using high-resolution solid-state 13 C nuclear magnetic resonance (NMR). Our NMR analysis revealed that, in polyisobutyrene rubber/polyisoprene rubber/CB composites, CB more easily distributes in polyisoprene rubber than in polyisobutyrene rubber. We found that more than 70% of CB is distributed into the polyisoprene rubber phase. The sum of the amounts of CB in both the polyisobutyrene rubber and polyisoprene rubber phases estimated by our method using 13 C NMR closely corresponds with the amount of CB originally added to the compound, verifying the validity of the NMR method. Further, we observed the distribution of CB in polyisobutyrene/polyisoprene rubber blends using transmission electron microscopy and the Carbon-Black-Gel method, which can only be used for unvulcanized rubber blends, for comparison. The results obtained using these three methods show similar tendencies, which confirms the accuracy of this method of using 13 C NMR to determine CB distribution in rubber blends. We establish the 13 C nuclear magnetic resonance (NMR) method as the best available method for the evaluation of carbon black (CB) distribution in rubber blend. We find that the line widths of NMR peaks increase as CB contents increase. Using this phenomenon it is found that, in polyisobutyrene rubber (IIR)/polyisoprene rubber (IR)/CB composites, CB more easily distributes in IR than in IIR. And we can estimate that more than 70% of CB is distributed in to the IR phase, irrespective of CB content.