High Double Bond Content of Polyisoprene Synthesis via Cationic Polymerization Synergistically Catalyzed by Tf2NH-Ionic Liquids

The highly selective cationic polymerization of isoprene has been a great challenge over the last 70 years. Here, a synergistic Tf2NH-ionic liquid (IL) catalytic system has been developed to address this issue under mild conditions. Tf2NH serves as a highly efficient catalyst for the cationic polymerization with 0.01 mol % loading, and its counteranion IL serves as a remarkable selectivity-controlled medium delivering low-molecular-weight (Mn < 1500 g/mol) polyisoprenes with excellent yields (up to 99%), double bond content (DBs, up to 99%), and trans-1,4 selectivities (>95%). Mechanistic investigations indicated that an IL cation could effectively suppress the reprotonation of double bonds in polymer chains by reducing the electron density, leading to highly linear desired polymers. The industrial application prospects are illustrated by the IL recycling process, which could be used for more than five rounds with excellent yields and DBs.