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

Abstract

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/nBu4NI 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.

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid–Base Pairs

“…Second, the resulting anion is weakly coordinating, which allows no formation of too stable, covalently bonded growing ends that could result in no cross-propagation between vinyl ether and IBO monomers with substantially different reactivities. Follow-up studies of the scope of the oxirane monomers revealed that the carbocation formation through the ring-opening of the oxirane-based oxonium is crucial. , Thus, oxiranes that can generate substituent-stabilized or tertiary carbocations, such as IBO and isoprene or butadiene monoxides, can be copolymerized with vinyl ethers because the oxirane-derived carbocation propagation sites could be readily formed and cross-react with the vinyl ether monomer. Aoshima and co-workers also examined cationic terpolymerization of vinyl ethers, cyclic ethers, and ketones.…”

Recent advances in applications of vinyl ether monomers for precise synthesis of custom-tailored polymers

“…Copolymerization of IPVE with 1-methoxy-2-methylpropylene oxide (MOMPO) was accomplished using a specific initiating system composed of CF 3 SO 3 H and nBu 4 NI [183] (Scheme 28). The ring-opening copolymerization resulted in IPVE-co-MOMPO product with unimodal molecular weight distribution (M n = 6,500 g•mol 1 , PDI = 1.73) subsequently hydrolyzed under acidic conditions to a low molecular weight product (M n = 1,700 g•mol 1 , PDI = 1.7).…”

Anionic Hybrid Copolymerization via Concurrent Oxa‐Michael Addition and Ring‐Opening Polymerizations

“…For example, Saegusa et al found that oxazolines and maleimides could undergo hybrid copolymerization via a zwitterionic mechanism . Aoshima’s group reported a series of hybrid copolymerizations between vinyl ethers and oxetane monomers . Polymerizations of this type rely on a long‐lived cationic propagating species and are based on a cationic mechanism.…”