Highly Stereocontrolled Ring-Opening Polymerization of Racemic Alkyl β-Malolactonates Mediated by Yttrium [Amino-alkoxy-bis(phenolate)] Complexes.

摘要: Yttrium [amino-alkoxy-bis(phenolate)]amido complexes have been used for the ring-opening polymerization (ROP) of racemic alkyl β-malolactonates (4-alkoxycarbonyl-2-oxetanones, rac-MLA(R) s) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature ortho-substituent on phenolate rings in metal ancillary dictated stereocontrol ROP, and consequently syndiotactic enrichment resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)-disubstituted ligands allowed first reported synthesis highly PMLA(R) s (Pr ≥ 0.95); conversely, bulky aryl ortho-substituted proved largely ineffective. All polymers characterized (1) H (13) C{(1) H} NMR spectroscopy, MALDI-ToF mass spectrometry DSC analyses. Statistical thermal analyses enabled rationalization chain-end control mechanism. Whereas obeyed a Markov first-order (Mk1) model rac-MLA(Bz) rac-MLA(All) , rac-MLA(Me) led to chain end-control second-order type (Mk2). DFT computations suggest that high ability featured Cl- Br-substituted does not likely originate from bonding between substituent growing polyester chain.