Ring-opening (Co)Polymerization Of ε-caprolactone And L-lactide Catalyzed By Zinc Complexes

In this thesis, the ring-opening (co)polymerization (ROP) of ε-caprolactone (s-CL) and L-lactide (L-LA) catalyzed by air-stable zinc dichloride complexes bearing (benzimidazolyl)pyridine alcohol ligands ([NNO] tridentate ligands) was investigated. Due to the existence of alkoxy group in the ligands, linear and cyclic (co)polyesters were obtained in the ring-opening (co)polymerization of ε-CL and L-LA inititated by zinc complexes in combination with methyllithium in the presence or absence of benzyl alcohol, repestively. This paper mainly includes four parts as follows:In the first part, the different metal complexes with different ligands, especially zinc complexes, used in the ring-opening (co)polymerization of cyclic esters were mainly summarized. The formation and mechanism of cyclic polyesters were also included.In the second part, a series of zinc complexes containing [NNO] tridentate ligands were synthesized and characterized by FT-IR,1H NMR and 13C NMR, elemental analysis. The X-ray single-crystal diffraction determined zinc complexes with a distorted trigonal bipyramidal configuration.In the third part, the ring-opening polymerization of ε-CL catalyzed by zinc complexes was studied. In combination with methyllithium, these zinc complexes were proved to be highly efficient initiators for the ROP of ε-CL. The catalytic systems kept highly active in a broad temperature range over 0-90 ℃; whereas, the higher reaction temperature resulted in lower Mn and broader PDI of PCLs. The PCLs produced by the current catalytic systems in the absence of BnOH were mainly cyclic with broader PDI; however, in the presence of benzyl alcohol, the PCLs were mainly linear with narrow PDI (1.12±1.85). The structures of these polymers were determined by 1H NMR,13C NMR and MALDI-TOF, and the possible mechanism of the formation of cyclic and linear polyesters was proposed.In the fourth part, the ring-opening copolymerization of ε-CL and L-LA forming block copolymers was studied. Firstly, the ROP of L-LA was studied and the similar regularity was observed. The complete conversions of monomer were achieved in 30 min in all the cases. In the absence of benzyl alcohol, polymers are mainly cyclic PLA with relatively broad PDI, whereas linear PLA with narrow PDI predominated in the presence of benzyl alcohol. Initiated by zinc complex 1/MeLi catalytic system, the block copolymers of ε-CL and L-LA were achieved by the sequential addition of monomers and characterized by FT-IR,1H NMR,13C NMR, GPC, DSC and TGA.