Alkoxyoxirane, a Unique Cyclic Monomer: Controlled Cationic Homopolymerization Mediated by Long-Lived Species and Copolymerization with Vinyl Ether via Alkoxy Group Transfer

1-Methoxy-2-methylpropylene oxide (MOMPO), an alkoxyoxirane that can generate a carbocation adjacent to an alkoxy group via ring-opening, was demonstrated to polymerize in a controlled manner with the use of a metal chloride as a Lewis acid catalyst. The choice of the initiating system is critical for the successful controlled homopolymerization of this alkoxyoxirane; a GaCl₃/THF system was observed to be the best combination for the initiating system. Furthermore, the copolymerization of MOMPO with isopropyl vinyl ether (IPVE) generated long-lived species when CF₃SO₃H/<i>n</i>Bu₄NI was used as the initiating system. Surprisingly, the reaction proceeded via the transfer of the alkoxy group in the IPVE unit. More specifically, the isopropoxy group at the penultimate IPVE unit transferred to the MOMPO-derived propagating cation after the crossover reaction from the IPVE-derived carbocation to MOMPO. This type of reaction creates a side group that possesses the ring-opened MOMPO structure with the isopropoxy group. The generation of copolymers via the “alkoxy-group transfer” mechanism is unique to the copolymerization in this study and was confirmed by ¹H, ¹³C, and 2D NMR analyses and by the acid hydrolysis and subsequent reacetalization reactions of the products