Ligand-free scandium alkyl and alkoxide complexes for immortal ring-opening polymerization of lactide

Publication date: Available online 3 September 2018Source: Journal of Organometallic ChemistryAuthor(s): Hongyan Xie, Chunji Wu, Dongmei Cui, Yang WangAbstractLigand-free Ln (CH2SiMe3)3 (THF)2 (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Er; 4: Ln = Y) and La(CH2C6H4-o-NMe2)3 (5) are employed as the initiators for ring-opening polymerization (ROP) of rac-lactide (rac-LA). Complex 4 solely is active but uncontrolled, while complex 1 is inert. In presence of excess benzhydrol, complexes 1–5 can promote the ROP of LA smoothly, in which the molecular weight distribution values of the resultant polymer are related to the radii of the rare-earth metals. Complex 1 displays high activity for the controlled ROP of LA, in which the benzhydrol act a dual role as chain-transfer agent and activator. The polymerizations proceed smoothly and efficiently in a wide range of benzhydrol feeding (3–150 equiv). The molecular weights of the obtained PLAs can be precisely controlled by the monomer loading with respect to that of benzhydrol, while the molecular weight distribution (MWD) maintains a very narrow level (PDI = 1.05–1.18). Every scandium centre by means of chain-transfer reaction with benzhydrol to generate the active species Sc(OCHPh2)3·THF (6), grows apparently up to 150 PLA polymer chains, showing a typical feature of an immortal polymerization.Graphical abstract

Source: Journal of Organometallic Chemistry - September 4, 2018 Category: Chemistry Source Type: research