Role of the Counteranion in the Stereospecific Living Cationic Polymerization of <i>N</i>-Vinylcarbazole and Vinyl Ethers: Mechanistic Investigation and Synthesis of Stereo-Designed Polymers
Hironobu Watanabe, Arihiro Kanazawa, Satoshi Okumoto, Sadahito Aoshima
Abstract
The effects of counteranions in the cationic polymerization of N-vinylcarbazole (NVC) and vinyl ethers were investigated to develop guidelines for stereospecific living cationic polymerization. The counteranion structure, such as the charge number, metal center, and ligand, was systematically examined using the CF3SO3H/onium halide/metal halide initiating system. As a result, the electronic properties rather than the steric bulkiness of the counteranion were demonstrated to be key to stereoregulation during the polymerization of N-vinylcarbazole. Fine-tuning the stereoregularity of the resultant polymers was achieved (mm = 45–95%) while maintaining the living nature of polymerization. Computational analysis indicated that the stereoregulation was attributed to electrostatic interactions between the counteranion and pendant aromatic rings. These findings also allowed stereospecific polymerization of vinyl ethers containing an aromatic ring in the pendant. Moreover, the successful synthesis of “stereo-designed” polymers, such as stereoblock and stereocontrolled block copolymers, was achieved by appropriately designing counteranions for living cationic polymerization.