One-Pot Synthesis of Natural Rubber-Based Telechelic cis-1,4-Polyisoprenes and Their Use To Prepare Block Copolymers by RAFT Polymerization

We investigate the one-pot synthesis of a new alpha,omega-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene (Pip) via metathesis degradation from natural rubber (NR) in the presence of the Grubbs second generation catalyst (OH) and a bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the metathesis degradation of the NR of 2 x 10(6) g mol(-1) molecular weight is performed in toluene at 25 degrees C using the ratio of [Ip](0)/[GII](0)/[CTA](0) = 100/1/1 (Ip = isoprene units), a cis-1,4-polyisoprene of 14 000 g mol(-1) after 4 h is obtained. The functionality estimated by H-1 NMR spectroscopy is equal to 1.5 +/- 0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by combination of H-1 NMR, C-13 NMR spectroscopy and FTIR. The influence of the CTA concentration was investigated. It was found that using higher concentrations of CTA ([Ip](0)/[GII](0)/[CTA](0) of 100/1/2 and 100/1/5) lead to form a perfectly telechelic cis-1,4-polyisoprene with a functionality of 2 with no significant difference in (M) over bar (n) values (approximately 6400 g mol(-1)) and in polydispersity indices (similar to 1.70). The new well-defined alpha,omega-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used successfully as macromolecular chain transfer agents (macroCTAs) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-BA](0)/[macroCTA](0)/[AIBN](0) = 500/1/0.4) in toluene at 60 degrees C leading to well-defined P(t-BA)-b-Plp-b-P(t-BA) triblock copolymers.