In recent years, the promotion of carbon neutrality has been required all over the world. We are implementing various initiatives that will lead to the reduction of CO₂ emissions. Weight reduction of automobile parts is also one of the efforts to reduce CO₂. Not only improving fuel efficiency but also reducing the amount of materials used, weight reduction leads to reduction of CO₂ emissions.

This paper introduces an example of weight reduction by developing a high-stiffness rubber material for an air cleaner hose. The important functions required for an air cleaner hose are negative pressure resistance, assembly performance, and sealing performance. In order to reduce the weight while maintaining these functions, it was necessary to develop a highly stiffness material with low temperature dependence of stiffness. In the development, we developed a new high-stiffness rubber material with low temperature dependence by using the rubber elasticity theory.

Marine pollution caused by plastic wastes increased the demand for recyclable polymer materials. In this review, we focus on the chemical recycle of vinyl polymers and polyesters, as they dominate the plastics market. Despite the easy procedure of synthesis, vinyl polymers are difficult to decompose due to the carbon backbone. Therefore, selective regeneration of monomers from polyolefins are difficult. In contrast, poly (methyl methacrylate) (PMMA) prepared by controlled radical polymerization can be depolymerized to regenerate the monomer. On the other hand, we have developed new vinyl polymers that efficiently regenerate their monomer precursors by main chain scission starting from the hydrolysis of the side group. For chemical recycling of polyesters, quantitative scission of ester bond is required. Recycling of PET has already been commercialized, but a more efficient method of the ester bond cleavage is required. Therefore, easily recyclable polyesters have been developed. In contrast, we have reported new unsaturated polyesters with chemical recyclability that recovered the monomer species. Instead of the ester bond cleavage, conjugate substitution reaction of the allyl-substituted methacrylate skeletons in unsaturated polyesters were performed under ambient condition.

For rubber vulcanizates or crosslinked rubbers, inherent characteristics of rubber elasticity are well known to be mainly controlled by the change in conformational entropy under deformation, causing constrained molecular mobility of rubbery network chains. In this part II of special lecture, ¹H-pulsed NMR method is applied to observe the motional heterogeneity in the crosslinked rubbers, related to effects of crosslink density and incorporation of reinforcing carbon black fillers on the tensile failure behaviors under various conditions. Furthermore, as for analysis of thermo-oxidative aging behaviors for the crosslinked rubbers, the relationships between the breaking stretch ratio in tensile measurements, λ_b, and NMR relaxation properties such as spin-spin relaxation time, T ₂, and residual dipolar coupling constant , D _res, were discussed to predict the failure properties of small pieces sampled from engineering rubber parts, for which tensile tests could not be easily performed.