Synthesis And Properties Citric Acid Polyester

With the development of society and the improvement of people’s living standards,the demand for polymer materials has increased sharply,and almost all of the polymer materials currently used are derived from non-renewable fossil resources and the long degradation cycle leads to environmental pollution.Therefore,the development of polymers and degradable polymers derived from renewable resources has become a research focus in the development of polymer materials.In this paper,with the goal of developing polyester with potential degradability,excellent performance and wide application,the following work was carried out with the biomass material citric acid as the main raw material.（1）In this research,two biomass materials-citric acid and glycerol were used as raw materials to synthesize hyperbranched citric acid polyesters（HBPE）.And two HBPE with different molecular weights and hydroxyl end groups were prepared by adjusting the reaction conditions.The chemical structure,degree of branching and molecular weights of the resulted HBPE were characterized by FT-IR,¹H NMR and GPC.The degree of branching was 85%,while the molecular weights were 4115 and 6011 g·mol^-1,respectively.Then two HBPE were further taken to prepare two different chemical cross-linking water-soluble polyesters:（a）HBPE-SA which HBPE was cross-linked by succinic acid through traditional chemical bonds,（b）HBPE-borax which HBPE was cross-linked by borax through dynamic boronic ester bonds.Rheological experiments show that there are reversible covalent bonds in HBPE-borax,and the mechanical strength and viscosity of HBPE-borax are affected by water content and molecular weight of HBPE.Generally HBPE-borax and HBPE-SA behave as very viscous liquids,and their viscosity remained around 3200 Pa·s at a shear rate of 30 s^-1.Since HBPE-borax had dynamic borate bonds,it had self-healing and p H stimuli-response properties.The hygroscopicity test indicated that the two polyesters can recover their viscosity in 20 minutes under the condition of relative humidity of 68%.Based on all characteristics described above,HBPE-borax and HBPE-SA both can be applied as a water-soluble biomass"sticker",and their adhensive properties were preliminarily explored.（2）Synthesis of citric acid base-shaped polyesters.The aliphatic monomer methylene citric acid was synthesized from citric acid,a renewable resource.Using methylene citric acid as a reactant,a partially cross-linked methylene citric acid polyester was obtained by melt polycondensation.Its structure and properties were characterized by FT-IR,¹H NMR and thermogravimetry.And explore the cause of cross-linking.In order to obtain thermoplastic aliphatic polyesters,acid chloride-diol esterification polymerization,transesterification polymerization and carboxyl group polymerization activated by acid-amine condensation reagents at room temperature have been tried,but they failed to obtain high molecular weight thermoplastic polymer due to low molecular weight.