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ABSTRACT: The random copolymers poly(LA‐ran‐CL) have improved properties of degradability, mechanical strength, elasticity, and permeability over the PLA and PCL homopolymers. However, the synthesis of such copolymers is still a great challenge in polymer chemistry. In this contribution, we develop a simple but well‐designed phenoxyimine Al complex (4) with bulky Ph2CH groups, which achieves controlled random copolymerization of rac‐LA and ɛ‐CL in a living manner (Ð = 1.06–1.09). The reactivity ratios of rac‐LA and ɛ‐CL (rLA and rCL) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit (LLA) and the caproyl unit (LCL) are in the range of 1.9–2.0 at different stages of conversion. In marked contrast, Al complexes (1–3) having less bulky substituents on the ligands only produce gradient copolymers. Furthermore, this strategy of catalyst design would be readily extended to other catalytic systems including β‐ketiminato Al complex (5). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 611–617 [ABSTRACT FROM AUTHOR]

The stoichiometric reaction of bis-phenolate ligands with AlMe3 afforded zwitterionic aluminum complexes Al1-Al3, which were characterized by NMR spectroscopy and elemental analysis. The solid state structure of Al2 was determined by single-crystal X-ray diffraction, which revealed a dinuclear feature. Two Al centers were bridged by two ligands and thus formed an unusual large 24-membered-ring metallacycle. In the presence of BnOH, Al1-Al3 were efficient for the ring-opening polymerization of ε-caprolactone in a controlled manner, and the efficiency was affected by substituents on the ligands. The polymerizations exhibited a feature of immortal catalysis with an excess of BnOH. [ABSTRACT FROM AUTHOR]

Stoichiometric reactions of YCl3(THF)3withpotassium 2-((arylimino)methyl)quinolin-8-olates or 2-(1-(arylimino)ethyl)quinolin-8-olatesin THF solution gave the mononuclear LYCl2(DMSO)2complexes 1–5in the presence ofDMSO and a representative dinuclear complex 6in theabsence of DMSO. All yttrium complexes were fully characterized byNMR measurements and elemental analysis, and the crystal structuresof complexes 1and 4–6were determined by single-crystal X-ray diffraction. The structuresindicate coordination number seven around the yttrium center and pentagonalbipyramidal geometries. The complexes all feature diapical YCl2moieties and one tridentate organic ligand in the equatorialplane. Upon reaction of the yttrium precatalysts 1–6with LiCH2Si(CH3)3aloneor with LiCH2Si(CH3)3together withBnOH, the ring-opening polymerization (ROP) of ε-caprolactone(ε-CL) occurred with high efficiency. Depending on conditions,the ROP of ε-CL produced polycaprolactone with narrow moleculardistribution and in a living manner. Theoretical studies of the chlorine/CH2SiMe3and Me3SiCH2/BnO ligandexchange reactions suggest that the replacement of the apical ligandscan proceed without significantly affecting the equatorial ligands.These results suggest that one of the apical Y–CH2SiMe3bonds within the LY(CH2SiMe3)2intermediate catalyzes the polymerization in the BnOH-freeprocess. Most polymers generated by BnOH-assisted catalysis possess Mnvalues that are similar to Mn,calvalues based on Y–OBn, suggesting that oneapical Y–OBn bond of the diapical LY(OBn)(CH2SiMe3) intermediate catalyzes most or all of the ring polymerizationof ε-CL. [ABSTRACT FROM AUTHOR]

A series of trimetallic yttrium complexes, L7Y3Cl2 [L = N-(2-methylquinolin-8-yl)-p-R-benzamides, 1: R = H; 2: R = OMe; 3: R = Me; 4: R = Cl], has been synthesized by the stoichiometric reaction of YCl3(THF)2 with the corresponding potassium amidates. All complexes have been characterized by elemental analysis and NMR spectroscopy. The molecular structure of complex 1 bearing seven amidate ligands was confirmed by single-crystal X-ray diffraction. Screening of these complexes, in the presence of BnOH, for ring-opening polymerization of caprolactone (ε-CL) revealed effective activities. [ABSTRACT FROM AUTHOR]

Graphical abstract The binary organocatalytic system comprised of CTPB and ureas is developed and shows both of high activity and selectivity for the ROP of cyclic esters. Highlights • A simple and synergetic binary catalytic system containing CTPB and urea has been developed. • The ROP of ε -CL and δ -VL was highly controlled. • The linear and three-arm star block copolymers were readily prepared. • The synergetic bifunctional mechanism was investigated. Abstract Phosphazenes have attracted considerable attention in the field of ring-opening polymerization (ROP) of cyclic esters. However, the application of phosphazenes as catalyst is subject to a trade-off between activity and selectivity (chain propagation versus transesterification/back-biting reaction, e.g., controlled polymerization). Despite extensive research efforts, the development of a new catalytic system having concurrent high activity and selectivity remains a great challenge. In this work, we report that the binary organocatalytic system comprised of cyclic trimeric phosphazene base (CTPB) and ureas shows both of high activity and selectivity for the ROP of ε -caprolactone (ε -CL) and δ -valerolactone (δ -VL) in the presence of alcohol as initiator. It is found that the introduction of ureas would significantly increase the catalytic selectivity during ROP without sacrificing the catalytic activity of CTPB. Moreover, the polymerizations catalyzed by the title catalytic system exhibit immortal characteristics and thus thousands equivalent of monomer could be converted to polymer efficiently with desired MWs and microstructures. Linear diblock copolymer AB and star copolymers (AB) 3 with three identical diblock arms could be readily synthesized by sequential copolymerization using different alcohols as initiators. [ABSTRACT FROM AUTHOR]