Thermal depolymerization and pyrolysis of cis-1,4-polyisoprene: preparation of liquid polyisoprene and terpene resin

The difference between controlled thermal depolymerization of natural and synthetic cis-1,4-polyisoprene as well as natural rubber unfilled reclaim and their pyrolysis is detailed in this study. The pyrolysis of 3,4-polyisoprene is also investigated. Controlled thermal depolymerization at 300-380 degrees C produces a liquid polyisoprene having a considerably lower molecular weight in comparison to the starting cis-1,1-polymer and also having a microstructure enriched in trans-1,4- and 3,4-units together with vinlydene units. The known mechanism of depolymerization has been updated based on electronic spectroscopy and FT-IR data which show that the end groups of liquid polyisoprene have dienes, trienes and tetraenes moieties as well as aldehydic groups conjugated with dienes and trienes. The possible low cost source of raw materials and the use of depolymerized liquid rubber is outlined. The pyrolysis of natural and synthetic cis-1,4-polyisoprene produces mainly dipentene (DL-limonene) with small amounts of isoprene and other products. 3,4-Polyisoprene-rich polymer yields mainly dipentene because of the pyrolysis of its 1,4-units. The residual of pyrolysis consists of 3,4-polyisoprene with these groups not cyclicized to a ladder polymer. The crude dipentene obtained from cis-1,4-polyisoprene pyrolysis can be conveniently converted into a valuable terpene resin usable in adhesive formulations and as thermoplastic rubber tackifier. (C) 1998 Elsevier Science B.V.