One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers by RAFT polymerization
Résumé
We investigate the one-pot synthesis of a new α,ω-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 (GII) and a bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the metathesis degradation of the NR of 2 × 106 g mol−1 molecular weight is performed in toluene at 25 °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 1H NMR spectroscopy is equal to 1.5 ± 0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by combination of 1H NMR, 13C 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 Mn values (approximately 6400 g mol−1) and in polydispersity indices (∼1.70). The new well-defined α,ω-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 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.