NATURAL RUBBER BIOSYNTHESIS: STILL A MYSTERY

ABSTRACT Currently, Hevea brasiliensis (the Brazilian rubber tree) is the only commercially available source of natural rubber (NR) for use in many products, which vary from tires to medical products such as adhesive bandages. H. brasiliensis NR is used in these products because after vulcanization, superior properties, which include elasticity, abrasion resistance, and efficient heat dispersion, result. Issues, such as increasing demand and risk of a single source, make a synthetic (manmade) NR an attractive option. However, after years of research efforts, the exact structure of high-molecular-weight NR is still unproven, and a synthetic NR with similar properties to H. brasiliensis NR still has not been developed. To create a replacement synthetic rubber for H. brasiliensis NR, we believe an understanding of NR biosynthesis is necessary. We present a view of NR biosynthesis from a polymer chemistry viewpoint that is based on insight into the mechanism and kinetics of living carbocationic polymerization.

Mechanical and Viscoelastic Characterization of Hyperbranched Polyisobutylenes

Structure-property relationships were investigated in hyperbranched polyisobutylenes, in comparison with commercial linear butyl rubber. The gel-free, soluble hyperbranched polyisobutylenes, synthesized by living carbocationic polymerization, had molecular weights, Mw≈400,000 to 1,000,000 g/mol, molecular weight distributions, MWD ≈1.2 to 2.6, and branching frequencies, BR ≈ 4 to 60. The mechanical and viscoelastic characterization of these polymers revealed interesting properties, including the characteristics of crosslinked rubbers.