Nylund Pamela V S, Monney Baptiste, Weder Christoph, Albrecht Martin
Department of Chemistry, Biochemistry & Pharmaceutical Sciences, University of Bern Freiestrasse 3 3012 Bern Switzerland
Adolphe Merkle Institute, University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland.
Catal Sci Technol. 2022 Jan 5;12(3):996-1004. doi: 10.1039/d1cy02143e. eCollection 2022 Feb 7.
Poly(lactic acid), PLA, which holds great promise as a biodegradable substitute of fossil resource-derived polyolefins, is industrially produced by the ring-opening polymerization of lactide using a potentially harmful tin catalyst. Based on mechanistic insights into the reaction of N-heterocyclic carbene (NHC) iron complexes with carbonyl substrates, we surmised and demonstrate here that such complexes are excellent catalysts for the bulk polymerization of lactide. We show that an iron complex with a triazolylidene NHC ligand is active at lactide/catalyst ratios of up to 10 000 : 1, produces polylactide with relatively high number-average molecular weights (up to 50 kg mol) and relatively narrow dispersity ( ∼ 1.6), and features an apparent polymerization rate constant of up to 8.5 × 10 s, which is more than an order of magnitude higher than that of the industrially used tin catalyst. Kinetic studies and end-group analyses support that the catalytically active species is well defined and that the polymerization proceeds a coordination-insertion mechanism. The robustness of the catalyst allows technical grade lactide to be polymerized, thus offering ample potential for application on larger scale in an industrially relevant setting.
聚乳酸（PLA）作为化石资源衍生聚烯烃的可生物降解替代品具有巨大潜力，它是通过使用潜在有害的锡催化剂对丙交酯进行开环聚合在工业上生产的。基于对N - 杂环卡宾（NHC）铁配合物与羰基底物反应的机理洞察，我们在此推测并证明此类配合物是丙交酯本体聚合的优良催化剂。我们表明，具有三唑亚基NHC配体的铁配合物在丙交酯/催化剂比例高达10000∶1时具有活性，能产生具有相对较高数均分子量（高达50 kg/mol）和相对较窄分散度（约1.6）的聚乳酸，其表观聚合速率常数高达8.5×10⁻⁴ s⁻¹，比工业上使用的锡催化剂高出一个多数量级。动力学研究和端基分析支持催化活性物种明确且聚合通过配位插入机理进行。该催化剂的稳健性使得工业级丙交酯能够聚合，从而在工业相关环境中大规模应用具有充足潜力。
