Study On Lewis Pairs Catalysts Mediated Contrllable Ring-opening Polymerization Of OCAs

The petroleum-based polymer compounds widely used in our daily life are mainly derived from fossil energy sources.Due to their non-degradable properties,they are often difficult to recycle and eventually cause environmental pollution.So we need greener materials to replace petroleum-based polymers.Poly(a-hydroxy acids)(PAHAs)have been widely studied as a class of biodegradable and biocompatible polymers.It is widely used in biomedical devices,packaging materials,drug delivery,tissue engineering and other fields.Poly(a-hydroxy acid)is traditionally obtained by ring-opening polymerization of lactide or glycolide,but the polymer prepared by this method has poor physical and mechanical behavior,poor heat resistance,and the lack of side chain functional groups which limits its large-scale application.O-carboxyanhydride(OCA),which is a activity substitute for lactone,can be prepared from a-hydroxy acid or a-amino acid having abundant side chain functional groups,and the rate of ring-opening polymerization is higher.It has attracted much attention and has become a new monomer for the synthesis of functional polyester materials.Therefore,it has become particularly important to develop catalytic systems that enable controlled ring opening polymerization of OCAs.In recent years,Lewis acid-base has rapidly developed in the field of controlled ring-opening polymerization of lactone monomers.So far,Lewis acid-base has reported less on the ring-opening polymerization of OCAs.So we are committed to the development of a controllable polymerization of OCAs by an acid-base composed of a simple and readily available Lewis acid and base.By screening different Lewis acids and Lewis bases,the acid-base pair consisting of anhydrous zinc acetate and DBU was finally determined as a catalytic system.The reaction conditions were optimized.At room temperature,benzyl alcohol was used as the initiator in dichloromethane.When both zinc acetate and DBU are 2 equivalents,50 equivalents of monomer controlled ring-opening polymerization can be completed in 3 hours,and the molecular weight distribution is 1.07,which has good controllability.This catalytic system has good applicability to different alcohol and amine initiators.The polymer NMR and MALDI-TOF MS analysis confirmed that the obtained a liner polymer terminated with a benzyl alcohol,and no side reactions such as transesterification occurred.Through the study of polymerization system kinetics,catalytic system interaction research and experimental data analysis,the possible reaction mechanism of polymerization reaction is proposed as bifunctional synergistic catalytic mechanism.