title: Different mechanisms at different temperatures for the ring-opening polymerization of lactide catalyzed by binuclear magnesium and zinc alkoxides.
abstract: Two binuclear magnesium and zinc alkoxides supported by a bis-salalen type dinucleating heptadentate Schiff base ligand were synthesized and fully characterized. The two complexes are efficient initiators for the ring-opening polymerization (ROP) of L-lactide, affording polymers with narrow polydispersities and desirable molecular weights. Interestingly, the mechanisms for the ROP of lactide are different at different temperatures. At a high temperature of 130 °C, a coordination-insertion mechanism is reasonable for the bulk melt polymerization of lactide. At a low temperature, the alkoxide cannot initiate the ROP reaction; however, upon the addition of external benzyl alcohol into the system, the ROP of lactide can smoothly proceed via an "activated monomer" mechanism. In addition, these complexes display slight stereo-selectivity for the ring-opening polymerization of rac-lactide, affording partially isotactic polylactide in toluene with a Pm value of 0.59.
authors: Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province and State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China. wujc@lzu.edu.cn.
authors: Yangyang
authors: Y
authors: Sun
authors: Yaqin
authors: Y
authors: Cui
authors: Jiao
authors: J
authors: Xiong
authors: Zhongran
authors: Z
authors: Dai
authors: Ning
authors: N
authors: Tang
authors: Jincai
authors: J
authors: Wu
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010087:Oxides / Q000737:chemistry; D058105:Polymerization; D011108:Polymers / Q000737:chemistry; D013237:Stereoisomerism; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D004146:Dioxanes; D010087:Oxides; D011108:Polymers; C091880:dilactide; D008274:Magnesium; D015032:Zinc