Fluorinated alkali metal catalysts for the Ring-Opening Polymerization (ROP) of rac-lactide. Effect of the M···F interactions in the polymerization control

Abstract

A series of lithium, sodium, and potassium complexes with different fluorinated phenoxo-imine ligands [M(O-2-(RN = CH)–C6H4] [R = 2,4,6-F3C6H2; 2,3-F2C6H3; 2-FC6H4] (1–3) (a,b,c) have been studied as catalysts for the Ring-Opening Polymerization (ROP) of rac-lactide. The sodium and potassium compounds are extremely active catalysts and reach quantitative conversions in just a couple of minutes when sodium or potassium are employed. In contrast, the lithium catalysts are slower but produce highly heterorich-PLA. The influence of fluorine substituents in the catalysts has been explored by analyzing their activity, the polymers tacticity and molecular weights in comparison to the fluorine-free derivatives [M(O-2-(RN = CH)C6H4] [R = 2-tBuC6H4; 2,6-iPr2C6H3] previously reported by us. The results show that the presence of fluorine atoms in the catalysts exerts a great influence on the polymerization reaction. The action of BnOH as chain transfer agent (CTA) has been also investigated for these ROP processes.