Synthesis,Characterization Of Alkali Metal Phenolates And Their Application In Ring-Opening Polymerization Of Lactide

Poly(lactic acid)is the most successful biodegradable polyester in the commercial market for development and application.Its appearance and application reach the two new major demands of polymers of biocompatibility and non-toxicity.The synthesis of poly(lactic acid)is mainly carried out by the ring-opening polymerization of lactide using a catalyst.In this process,the choice of a catalyst is particularly important.Different catalysts will afford poly(lactic acid)different stereoregularities which will determine the physical properties of poly(lactic acid).So far,many effective catalysts have been discovered and successfully applied to the ring-opening polymerization of lactide.In this part,the metal catalyst still dominates,and there are many application examples,such as alkali metal complexes,alkaline earth metal complexes,rare earth complexes,and complexes of aluminum,titanium,zirconium,hafnium and indium.The advantages of non-toxic and low-cost sodium and potassium metals make themself outstanding among many metal catalysts/initators.Our research group has developed a crown ether monophenol sodium and potassium catalyst system,which can catalyze the formation of polylactic acid with high stereoregularity.However,the system suffers from the conditions of low temperature without the aid of the crown ether,and therefore,further improvement of the system is required.This thesis focuses on the development of the stereoselective sodium and potassium metal complexes in the lactide ring-opening polymerization,and the following three parts are included in this thesis:The first chapter mainly introduces the research status of stereoselective ring-opening polymerization of lactide,and introduces some catalysts that have been successfully applied to the ring-opening polymerization of lactide.In the second chapter,the synthesis and characterization of sodium and potassium ion complexes with tetradentate aminobisphenol as ligands and their applications in the ring-opening polymerization of lactide were presented.The results show that the tetradentate aminobisphenol ion pair complex can successfully initiate the ring-opening polymerization of lactide,and has a high isotactic selectivity(P_m=0.82)and a molecular weight of 50.1 kg/mol.In the third chapter,a bisphenol multidentate complex centered on potassium metal was designed.It is hoped that the metal center will be more stable for the chelation effect,and the selectivity and controllability will be considered.As expected,the multidentate ligand like 18-crown-6 can effectively encapsulate potassium ions,which formed a tetranuclear dimer complex.This complex applied to the ring-opening polymerization of lactide with the selectivity value up to P_m=0.81.The molecular weight is up to 88.8 kg/mol,and rac-LA can be efficiently ring-opened in the presence of traces of water.