Amine-Bridged Bis(phenolate) Aluminum Complexes as High-Efficiency Catalysts for Controlled Polymerization of...

Poly(trimethylene carbonate) (PTMC) is currently attracting increasing attention due to its notable biocompatibility and biodegradability. High-molecular-weight PTMCs would find a wider range of practical applications; however, their preparation methods are still limited. In this work, a series of aluminum complexes supported by amine-bridged bis(phenolate) ligands were synthesized and employed as the catalysts for TMC polymerization. Alkane elimination reaction of the amine-bridged bis(phenolate) proligand H₂L (L = (CH₃)₂NCH₂CH₂N[CH₂-(2-OH-3-R¹-5-R²-C₆H₂)]₂) with one equivalent of AlEt₃ afforded the corresponding aluminum ethyl complexes LAlEt (R¹ = R² = Bu, L¹, 1; R¹ = R² = Me, L², 2; R¹ = R² = Cl, L³, 3; R¹ = R² = cumyl, L⁴, 4). Treatment of these aluminum ethyl complexes with one equivalent of ROH (R = PhCH₂ or CF₃CH₂) produced the aluminum alkoxide complexes L¹Al(OCH₂Ph) (5), L²Al(OCH₂Ph) (6), L³Al(OCH₂Ph)(THF) (7), and L⁴Al(OCH₂CF₃) (8). The catalytic behavior of these complexes for TMC polymerization revealed that the polymerization kinetics was a first-order dependence on both monomer and initiator concentration in THF, and the polymerization proceeded in a controlled fashion, providing PTMC with a high molecular weight (M_n >10⁵ g/mol).