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

• Published in: Macromolecules 2011-03, Vol.44 (6), p.1372-1384
• Main Authors: Kostjuk, Sergei V, Ouardad, Samira, Peruch, Frédéric, Deffieux, Alain, Absalon, Christelle, Puskas, Judit E, Ganachaud, François
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma1027966

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 M n ≤ 5000 g mol−1 and a molar mass distribution or MMD (M w/M n ≤ 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 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(C6F5)3-initiated cationic polymerization of isoprene. In aqueous media, the cationic polymerization of isoprene with 1/B(C6F5)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 (≤1200 g mol−1) and M w/M n ≤ 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 α-end and an olefinic terminal group can be produced almost exclusively in a trans-1,4 configuration (92−96.5%).