The cationic polymerization of isoprene using the 1-(4-methoxyphenyl)ethanol (1)/B(C 6 F 5 ) 3 initiating system in solution (dichloromethane or R,R,R-trifluorotoluene) and in aqueous media (suspension, dispersion, or emulsion) is reported. In organic solvents the reaction proceeded by controlled initiation via 1, followed by irreversible termination, thus affording polymers with a numberaverage molar mass M n e 5000 g mol -1 and a molar mass distribution or MMD (M w /M n e 2.5) and rather high content of intact double bonds (g70%) in the polymer backbone. In particular, using R,R,R-trifluorotoluene as polymerization solvent in place of dichloromethane promoted the synthesis of polyisoprene chains with M w /M n ∼ 1.4 and larger content of intact double bonds (up to 88%). In the absence of 1, polyisoprenes with fairly high molar mass (M n up to 18 000 g mol -1 ) and M w /M n < 2.4 were synthesized through adventitious water/B(C 6 F 5 ) 3 -initiated cationic polymerization of isoprene. In aqueous media, the cationic polymerization of isoprene with 1/B(C 6 F 5 ) 3 proceeded without any side reactions (cyclization, branching). However, aqueous conditions afforded only moderate yield (up to 60% monomer conversion) and polyisoprenes with low M n (e1200 g mol -1 ) and M w /M n e 1.7 were obtained. By comparing different characterization data (NMR, mass spectrometry), it was demonstrated that under appropriate conditions (in organic solvents at -30 °C or in aqueous media) polyisoprenes carrying the initiator fragment from 1 at the R-end and an olefinic terminal group can be produced almost exclusively in a trans-1,4 configuration (92-96.5%).

International audienceIn this paper, more than 70 years of cationic polymerization of isoprene (IP) are reviewed. Up to now, the controlled or living cationic polymerization of IP was never reported due to numerous side reactions, including chain transfer, cyclization, and cross-linking reactions that were very difficult to control. Cationic polyisoprenes (PIPs) are thus described to be mainly 1,4-trans with saturated/cyclized sequences. Although progress was made for their characterization due to many analysis techniques, cationic PIPs are still not yet fully characterized, particularly the saturated sequences. As a consequence, even if suggestions are proposed, polymerization mechanism is still not fully elucidated