Catalytic synergy using Al(III) and Group 1 metals to accelerate epoxide and anhydride ring-opening copolymerization

Journal article

The controlled synthesis of polyesters via epoxide/anhydride ring-opening copolymerization is a versatile and generally applicable method to make many sustainable polymers, but catalyst activities are limited and the required catalyst loadings are typically high. Here, novel heterodinuclear complexes, featuring Al(III)/M(I) (M = Na, K, Rb, Cs), show exceptional activities for phthalic anhydride and cyclohexene oxide copolymerization (catalyst = Al(III)/K(I), turnover frequency = 1072 h–1, 0.25 mol % catalyst loading vs anhydride, 100 °C). The Al(III)/K(I) catalyst is also tolerant to low loadings, maintaining a good performance at 0.025 mol % catalyst vs anhydride loading and 0.005 mol % vs epoxide. It rapidly polymerizes other epoxide/anhydride combinations yielding various semi-aromatic, rigid, and/or functionalizable polyesters and also shows activity in carbon dioxide/epoxide copolymerizations. The results of structure–activity, X-ray crystallography, polymerization kinetics, and density functional theory investigations support a mechanism with chain growth alternation between the metals. The rate-limiting step is proposed to involve epoxide coordination at Al(III) with K(I) carboxylate attack. Future exploitation of abundant and inexpensive Group 1 metals to deliver synergic polymerization catalysts is recommended.

Authors: Diment, WT; Gregory, GL; Kerr, RWF; Phanopoulos, A; Buchard, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: ACS Catalysis
• Volume: 11
• Issue: 20
• Pages: 12532-12542
• Publication date: 2021-09-28
• Acceptance date: 2021-09-09
• DOI: 10.1021/acscatal.1c04020
• EISSN: 2155-5435
• Language: English
• Keywords: polyesters; FFR; aluminum catalysts; ring-opening copolymerization; group 1 metal carboxylate; mechanism; heterodinuclear cooperativity