Cationic Polymerization of Phenyl Vinyl Ethers: Investigations of the Propagation Mechanism, the Living Polymerization of Ortho-Substituted Derivatives, and the Step-Growth Polymerization of Divinyl Derivatives
2020
Asakawa, Tomohito | Kanazawa, Arihiro | Aoshima, Sadahito
The cationic polymerization of phenyl vinyl ether (PhVE) was investigated to elucidate the reason it is much more difficult to obtain high-molecular-weight polymers of PhVE than with alkyl vinyl ethers. The detailed analysis of the products by NMR spectroscopy indicated that the propagation proceeded not via a sequential vinyl-addition reaction but via an intramolecular Friedel–Crafts reaction between a PhVE-derived carbocation and the phenyl ring of the penultimate unit and subsequent generation of another carbocation via the cleavage of the sec-benzylic ether moiety of the resulting chromane-type structure. The intermolecular Friedel–Crafts reaction also likely occurred in the polymerization conducted in dichloromethane. The introduction of electron-withdrawing substituents into the phenyl ring of PhVE did not suppress the intramolecular Friedel–Crafts reactions, whereas the blocking of the ortho-positions of the ring by methyl substitution resulted in propagation by the vinyl-addition reactions. In particular, the cationic polymerization of 2,4,6-trimethylphenyl vinyl ether proceeded in a living manner under the optimized conditions. In addition, the copolymerization of PhVE with p-methoxybenzaldehyde occurred via vinyl- and carbonyl-addition reactions without Friedel–Crafts reactions, resulting in a polymer with an alternating sequence. Moreover, such a Friedel–Crafts reaction was successfully employed as a bond-forming reaction for the synthesis of polymers from 1,4-divinyloxybenzene via a step-growth mechanism.
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