Synthesis of Soluble Poly(methacrylic anhydride) by Radical Cyclopolymerization

Cyclopolymerization of methacrylic anhydride (MAA) by conventional radical polymerization using cobaloxime boron fluoride (CoBF) as a chain transfer agent allows high conversion synthesis of fully soluble cyclopoly(methacrylic anhydride) (PMAA). Specifically, soluble PMAA was attainable even at moderate MAA concentrations with no cross-linking in the presence of CoBF. This was achieved by studying various MAA concentrations and temperatures with and without CoBF and examining these parameters' impact on the PMAA microstructure, including the acyclic, cyclic, and cross-linked forms. Infrared and 1H nuclear magnetic resonance (NMR) spectroscopy confirmed the formation of cyclic anhydride groups and the presence of unsaturated end groups created in the presence of CoBF. The molecular weight of the synthesized PMAA decreased with an increase in CoBF concentration. 13C NMR spectra of PMAA confirmed the cyclization through the presence of a single peak in the carbonyl region. Importantly, the nondiluted MAA polymerization in the presence of CoBF led to the production of cyclic six-membered soluble polymers. On the other hand, cross-linked PMAA resulted from the polymerization of MAA at 3.4 M monomer concentration in the absence of CoBF.