Synthesis of cyclic Poly(methyl methacrylate) via N-Heterocyclic carbene (NHC) initiated-anionic polymerization and subsequent ring-closing without need of highly dilute conditions

Abstract

A cyclic polymethacrylate was prepared via the anionic polymerization of methyl methacrylate (MMA) initiated by a 1:1 adduct of methyl sorbate (MS) and a N-heterocyclic carbene (NHC) without the need for highly dilute conditions, because an α-terminal imidazolimium group is neighboring to the propagating anion during the polymerization. The polymerization proceeded quantitatively using methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) as the Lewis acid to give the poly (MMA) with the MS unit in the α-terminus, and an Mn of 7.2 × 103–29.1 × 103 with a molecular weight distribution (Mw/Mn = 1.16-1.56). From proton (1H) NMR and matrix assisted laser desorption/ionization (MALDI-TOF) mass spectra, coupled with size exclusion chromatography (SEC) of the poly (MMA) produced before and after ozonolysis of the internal carbon-carbon double bond in the MS unit, we found that ring-closing reaction was induced by nucleophilic substitution of the propagating anion to the neighboring carbon of the α-terminal carbenyl (imidazolimium) group to synthesize cyclic poly (MMA) following complete the monomer consumption.