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Air-Stable Copper Derivatives as Efficient Catalysts for Controlled LactidePolymerization: Facile Synthesis and Characterization of Well-DefinedBenzotriazole Phenoxide Copper Complexes

By Chen-Yu Li, Shi-Jie Hsu, Chin-lung Lin, Chen-Yen Tsai, Jun-Han Wang, Bao-Tsan Ko, Chia-Her Lin and Hsi-Ya Huang


Air-stable copper catalysts supported by bis-BTP ligands (BTP = N,O-bidentate benzotriazole phenoxide) were synthesized and structurally characterized. The reactions of Cu(OAc)2·H2O with 2.0 molar equivalents of sterically bulky 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (CMe2PhBTP-H) and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol (t-BuBTP-H) in refluxing ethanol solution afforded monomeric copper complexes [(CMe2PhBTP)2Cu] (1) and [(t-BuBTP)2Cu] (2), respectively. The four-coordinated copper analogue [(TMClBTP)2Cu] (3) resulted from treatment of 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol (TMClBTP-H) as the ligand under the same synthetic method with ligand to metal precursor ratio of 2:1, but treatment of complex 3 in acetone gave five-coordinated monomeric complex [(TMClBTP)2Cu(Me2CO)] (4). X-ray diffraction of single crystals indicates that Cu complex 4 assumes a distorted square pyramidal geometry, penta-coordinated by two BTP ligands, and one Me2CO molecule. Catalysis for lactide (LA) polymerization of BTP-containing Cu complexes in the presence of various alcohol initiators was investigated. Complex 3 initiated by 9-anthracenemethanol catalyzes the ring-opening polymerization effectively not only in a “living” fashion but also in an “immortal” manner, yielding polymers with the predictable molecular weights and narrow molecular weight distributions. Initiations from multifunctional alcohols were able to produce PLLAs with two-arm linear and three-arm star-shaped molecular architectures. The controlled character of Cu complex 3 also enabled us to synthesize the PEG-b-PLLA copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3840–384

Topics: benzotriazole phenoxide, biodegradable, catalysis, copper, lactide, polyesters, ring-opening polymerization (ROP)
Year: 2014
DOI identifier: 10.1002/pola.26780
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