This work focuses on a novel controlled radical polymerization method under aerobic conditions by incorporating Lewis base-catalyzed, complexation-induced hydrogen atom transfer (LBCI-HAT) agents containing hydrosilane, crown-ether, and alkali metal Lewis base catalysts. The time-resolved measurements were performed using the FT-NIR by monitoring a distinct overtone of the vinylic C–H stretching at 6132 cm-1 that does not overlap other bands from solvent or polymer. A series of polymerization conditions was carried out for styrene monomers, incorporating a silane/ alkali metal Lewis base (e.g., KOtBu) pair in the presence of 18-crown-6-ether. The values of ln([M0]/[Mt]) were obtained by linear fitting of the kinetic plots by in situ FT-NIR spectroscopy. Extensive kinetic studies were performed on the steric effects of silicon substituents (H2SiEt2, HSiEt3, H3SiPh1, H2SiPh2, and HSiPh3). Moreover, we successfully synthesized the block copolymer of poly[styrene/methyl methacrylate] with LBCI-HAT. Upon the polymerization of PS, MMA was then added in the open air without the addition of LBCI-HAT catalyst in the solution. Successful chain extensions of PS with MMA were confirmed by GPC and 1H NMR. We concluded that this alkali metal Lewis base-catalyzed, HAT living radical polymerization can be controlled by an equilibrium between propagating radical species Pn and initiator. The LBCI-HAT polymerization method offers potential for polymer architecture manufacture and a variety of industrial polymerization processes by successfully producing polymers by performing block copolymerization and scale-up polymerization under mild conditions.

Sustainable hydrogen atom transfer-mediated controlled radical polymerization

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