Carbocationic Polymerization of Isoprene Co-initiated by B(C6F5)3: An Alternative Route toward Natural Rubber Polymer Analogues?

Abstract

The cationic polymerization of isoprene using the 1-(4-methoxyphenyl)ethanol (1)/B(C6F5)3 initiating system in solution (dichloromethane or α,α,α-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 number-average molar mass Mn ≤ 5000 g mol−1 and a molar mass distribution or MMD (Mw/Mn ≤ 2.5) and rather high content of intact double bonds (≥70%) in the polymer backbone. In particular, using α,α,α-trifluorotoluene as polymerization solvent in place of dichloromethane promoted the synthesis of polyisoprene chains with Mw/Mn ∼ 1.4 and larger content of intact double bonds (up to 88%). In the absence of 1, polyisoprenes with fairly high molar mass (Mn up to 18 000 g mol−1) and Mw/Mn < 2.4 were synthesized through adventitious water/B(C6F5)3-initiated cationic polymerization of isoprene. In aqueous media, the cationic polymerization...