Vinyl alcohol–methacrylatecopolymers have intriguing functionally rich structures
but are synthetically inaccessible from vinyl acetate, the traditional
precursor to polyvinyl alcohol. We report a solution via BN 2-vinylnaphthalene
(BN2VN), an aromatic vinyl borane monomer. Conventional free radical
copolymerization of BN2VN and methyl methacrylate (MMA) is facile.
Conversion of BN2VN side chains to VA side chains is accomplished
in organic solvents with Me3NO·2H2O and
avoids MMA hydrolysis. The VA–MMA copolymer rapidly lactonizes
to give an unprecedented macromolecule bearing both acyclic and cyclic
ester residues. Methanolysis furnishes the statistical copolymer bearing
vinyl alcohol, methyl methacrylate, and lactone residues. tert-Butyl methacrylate-BN2VN copolymers were shown to not
lactonize.
The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2‐vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (Mw ~ 105 g mol−1) BN2VN homopolymers and BN2VN‐styrene copolymers were obtained.
The first solid-state characterization of statistical copolymers of vinyl alcohol and styrene (poly(VA-stat-St)) by cross-polarization magic angle spinning (CP-MAS) spectroscopy is described. Poly(VA-stat-St) is not available from the traditional feedstocks styrene (St) and vinyl acetate (VAc) due to a mismatch in reactivity ratios. BN 2-vinylnaphthalene (BN2VN) is a synthetic solution to this challenge as it copolymerizes with activated monomers (e.g., styrene, methyl methacrylate), and the BN naphthalene side chain can be oxidatively converted to hydroxyl (−OH) side chains. While high levels of BN2VN incorporation are readily achieved (e.g., >75 mol % BN2VN), prior work has identified that poly(VA-stat-St) is poorly soluble in organic solvents when the molar fraction of VA exceeds 0.50, presumably due to the hydrophilic character of the hydroxyl group as well as possible interchain hydrogen bonding. Circumventing this solubility challenge, we describe quantitative solid-state 13 C CP-MAS spectra demonstrating high conversion (85−99%) of poly(BN2VN-stat-St) to poly(VA-stat-St). 11 B CP-MAS confirmed the removal of organoborane functional groups.
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