Specific Polymerization Mechanism Involving β-Scission of Mid-Chain Radical Yielding Oligomers in the Free-Radical Polymerization of Vinyl Ethers

Butyl vinyl ether (BVE) was polymerized radically, and the resultant oligomeric poly(BVE)s were characterized mainly using MALDI-TOF-MS spectrometry. For a further structural identification, the poly(BVE) obtained in bulk was subsequently subjected to 1H NMR measurement. Notably, an intensive peak assignable to −CH2C(O)CH2− protons was observed unexpectedly although a peak assignable to −CHO proton as the terminal end-group generated via β-scission of growing polymer radical as a presumed chain-end forming reaction appeared only weakly. Thus, a plausible chain-end forming reaction would be the intramolecular (backbiting) hydrogen abstraction to form mid-chain radical which subsequently undergoes β-scission resulting in oligomeric poly(BVE) with carbonyl group in the polymer backbone. Then, the specific polymerization mechanism involving β-scission of mid-chain radical yielding oligomers is discussed. The hydrogen abstraction ability of growing poly(BVE) radical was checked by using toluene as a solvent having labile hydrogen. The dependence of the degree of polymerization on initiator concentration was examined because the occurrence of primary radical termination was remarkable, probably leading to reduced chain length. Finally, the reinitiation reaction by butyl group generated via β-scission of mid-chain radical was pursued.