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Electron rich salen-AlCl catalysts as efficient initiators for the ring-opening polymerisation of rac-lactide

2019; Elsevier BV; Volume: 119; Linguagem: Inglês

10.1016/j.eurpolymj.2019.07.017

1873-1945

Anand J. Gaston, Gabija Navickaite, Gary S. Nichol, Michael P. Shaver, Jennifer A. Garden,

Organometallic Complex Synthesis and Catalysis

The ring-opening polymerisation of lactide is a useful means to prepare biodegradable materials with well controlled polymer architectures and bespoke material properties. While homogeneous ligand-Al-OR complexes have shown great success in this field, initiation from ligand-AlCl complexes has lagged behind. Here, we report four new salen-AlCl complexes featuring NEt2-substituents, which display high catalyst activities towards rac-lactide ring-opening polymerisation (kobs < 1.9 × 10−3 s−1) via in situ activation with a single equivalent of propylene oxide. Incorporating Lewis basic NEt2 groups into the ligand scaffold not only improves the initiation efficiency but also avoids the need for a Lewis basic co-catalyst and excess epoxide. Notably, studies of our amino-substituted catalysts reveal that the formation of a hexacoordinate aluminate species may hinder rather than enhance catalytic activity.