Zinc complexes coordinated by bipyridine-phenolate ligands as an efficient initiator for ring-opening polymerization of cyclic esters

• Published in: Polymer (Guilford) Vol. 56; pp. 237 - 244
• Main Authors: Hsieh, Yi-Liang, Lin, Yi-Chien, Lee, Gene-Hsiang, Peng, Chi-How
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.01.2015
• Subjects: Bipyridine-phenolate; Block copolymers; Distortion; Esters; Formations; Ligands; Molecular weight distribution; Polymerization; Ring-opening polymerization; Synthesis; Zinc; Zinc complexes; Ring-opening polymerization; Zinc complexes; Bipyridine-phenolate
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2014.12.001

A series of zinc complexes coordinated by different bipyridine-phenolate (BpyPh) ligands, 2-([2,2′-bipyridin]-6-yl)-4,6-di-tert-butylphenol (BpyPh2,4-tBu-H, 3) and 2-([2,2′-bipyridin]-6-yl)-4-(tert-butyl)phenol (BpyPh4-tBu-H, 4) have been synthesized. The reaction of BpyPh2,4-tBu-H with ZnEt2 gave a six-coordinated complex of [(BpyPh2,4-tBu)2Zn] (5) with the distorted octahedral geometry. However, the dinuclear complexes of [(BpyPh)Zn(μ-OBn)]2 (6 and 7) were formed when benzyl alcohol was added and then can be converted to mononuclear zinc benzylalkoxide species by the increased temperature. The ε-CL and L-LA polymerizations initiated by complex 6 showed the living characteristics of narrow molecular weight distribution (PDIs < 1.15) and the capability of block copolymer synthesis demonstrated by the formation of PCL-b-PVL and PCL-b-PHB. The ring-opening polymerizations of cyclic esters initiated by complex 5, however, was not effective possibly due to the highly steric hindered metal center. [Display omitted] •Designed ligands were obtained via a simple, one-pot synthetic process.•Well controlled ring-opening polymerization of various cyclic esters was achieved.•Different block copolymers of lactones have been synthesized.