Transpolyisoprene

Transpolyisoprene, also called trans-1,4-polyisoprene, is a polymer formed from isoprene monomers linked primarily by trans-1,4 bonds. This contrasts with cis-1,4 polyisoprene, the configuration common to natural rubber. The trans arrangement confers a higher regularity along the polymer chain, which tends to increase crystallinity and stiffness and reduces elasticity relative to cis-polyisoprene.

In nature, trans-1,4 polyisoprene occurs predominantly in gutta-percha, a hard, waxy substance obtained from the milky latex of certain tropical trees such as Palaquium gutta. Gutta-percha is largely trans-1,4-polyisoprene with trace impurities. It was historically used as insulation for underwater telegraph cables and later found use as a dental root canal filling material when softened by heat.

Synthetically, trans-1,4 polyisoprene can be produced by polymerization of isoprene with catalysts that favor trans-1,4 addition. Such polymers are more crystalline and have higher melting points than cis rubber, making them harder and less elastic. They are generally thermoplastic and can be melted and remolded under heat.

Beyond gutta-percha, transpolyisoprene has been explored for specialty rubbers, adhesives, and coatings, though its use is limited by mechanical properties compared with cis rubber. In dentistry, gutta-percha is primarily used as a root canal filling material, often in combination with fillers such as zinc oxide to achieve desirable handling and physical properties.