B(C6F5)3-based Lewis pair-catalyzed acrylate polymerization: Lewis base effects on pairing interactions

Abstract

Acrylate polymerizations catalyzed by Lewis pairs (LP) composed of B(C6F5)3 and various Lewis bases (phosphines, amines, and an N-heterocyclic carbene) in dichloromethane were investigated using two procedures based on different monomer/catalyst addition sequences. In procedure 1, Lewis bases were added to B(C6F5)3-activated n-butyl acrylate (nBA), and the polymerization proceeded quantitatively using all Lewis bases at a wide temperature range (−60 °C to 30 °C). A low nucleophilic Lewis base Et3N also initiated the polymerization even at −60 °C. However, t-butyl acrylate was not polymerized, as LP promoted its conversion into acrylic acid and isobutene. In procedure 2, nBA was added to interacting LPs; the type of Lewis base significantly affected the polymerization results. Specifically, polymerization was not observed when 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and PnBu3 were applied; however, similar to the reaction in procedure 1, PPh3, PtBu3, and 1,4-diazabicyclo[2.2.2]octane (DABCO) initiated nBA polymerization. The pairing interactions between LBs/B(C6F5)3 (PPh3, Et3N, DBU, and DABCO) were investigated using the shift of 19F nuclear magnetic resonance signals, demonstrating that weak interacting LPs efficiently initiated the polymerizations in procedure 2. Acrylate polymerizations catalyzed by Lewis pairs (LP) composed of B(C6F5)3 and various Lewis bases were investigated using two procedures based on different monomer/catalyst addition sequences. When Lewis bases were added to B(C6F5)3-activated n-butyl acrylate (nBA) (procedure 1), the polymerization proceeded quantitatively using all Lewis bases. In contrast, the type of Lewis base significantly affected the polymerization results when nBA was added to interacting LPs (procedure 2). 19F nuclear magnetic resonance analysis of the LPs indicated that weakly interacting LPs efficiently initiated the polymerizations in procedure 2.