Chemoselective Polymerization of 2-(Acryloyloxy)ethyl Methacrylate Enabled by B(C ₆ F ₅ ) ₃ -Stabilized <i>s-cis</i> and <i>s-trans</i> Monomer Conformations

Chemoselective polymerization of divinyl monomers enables the synthesis of polymers bearing reactive side chains, which are versatile precursors for functionalized polymers and nonlinear architectures. However, retaining the highly polymerizable functional groups, such as α,β-unsaturated carbonyls, during polymerization is challenging. In this study, the polymerization of 2-(acryloyloxy)-ethyl methacrylate (<b>1</b>) using Lewis pair catalysts composed of B-(C₆F₅)₃ with PPh₃ or PCy₃ proceeded exclusively at the acryloyl moiety without cross-linking, thus retaining the methacryloyl group in the polymer side chain. Nuclear magnetic resonance spectroscopy and density functional theory computations revealed that the complete chemoselectivity of this reaction, preferentially occurring at the acryloyl moiety rather than the methacryloyl moiety, could be attributed to the conformational preference of the <b>1</b>-B-(C₆F₅)₃ complexes. Specifically, a highly electrophilic <i>s-trans</i> conformer formed upon coordination of the acryloyl group, whereas a much less reactive <i>s-cis</i> conformer formed upon coordination of the methacryloyl group. Additionally, acrylic copolymers of <b>1</b> bearing multiple methacryloyl groups were synthesized and employed as polymeric cross-linkers for the radical photopolymerization of ethyl acrylate (EA). The resulting polyEA elastomers exhibited increased stress at high strains and greater mechanical robustness than elastomers synthesized from a divinyl cross-linker.