Synthesis And Properties Of The Biodegradable Thermoplastic Polyester Elastomer

Thermoplastic polyester elastomer(TPEE)is one of the thermoplastic elastomers(TPEs),which not only has high elasticity and thermoplasticity,but also has wide temperature range and excellent oil resistance,and has been extensively applied in many fields.However,the hard segment of TPEE,aromatic polyester,was made from fossil resources,which leads to poor biodegradability,high hardness and low elasticity resilience.In this paper,a novel biodegradable thermoplastic polyester elastomer(BTPE)with low hardness and high tensile recovery was prepared using aliphatic saturated dibasic acids and diol by means of melt polycondensation and chain extension reaction.The relationship between structure of BTPE and its crystallization ability,mechanical properties,thermal stability and biodegradability was discussed,and its cytocompatibility was preliminarily explored.1.The preparation and characterization of hard segment polyester prepolymer(HPE)and soft segment polyester prepolymer(SPE).A series of HPE and SPE with different molecular structure and molecular weights were designed and prepared using aliphatic saturated dibasic acid(succinic acid,adipic acid and sebacic acid)and aliphatic saturated dibasic alcohol(1,3-propanediol and 1,4-butanediol)by means of melting polycondensation,and the synthesis technologies were optimized to synthesize the HPE and SPE.The structure of HPE and SPE was characterized by FTIR and1H-NMR,respectively.The thermal properties and crystalline properties of polyester prepolymers were measured by differential scanning calorimeter(DSC),polarizing microscope(POM)and wide-angle X-ray diffraction(WXRD),and the relationship and the mechanism between structure and properties were discussed.The experimental results showed that HPE is a hydroxyl-terminated crystalline aliphatic polyester with simple structure and strong crystallization ability,which is suitable for the hard segment structure of BTPE.SPE is a hydroxyl-terminated aliphatic saturated random copolyester with many repetitive units and high flexibility,which can be used as soft segment structure of BTPE.2.Preparation and properties of BTPE.4,4'-diphenylmethane diisocyanate(MDI)was used as chain extender to carry out chain extension reaction between HPE and SPE.A series of BTPE with different structures and properties were synthesized by adjusting molecular structure and molecular weights of polyester prepolymers,the mass ratio of HPE to SPE,and other factors.The crystallization ability,mechanical properties and thermal stability of BTPE were investigated.The experimental results indicated that BTPE is an aliphatic saturated polyester block polymer with Mw of up to270000 g/mol,which has wide operating temperature range(Tg is about-50 o C,Tm is about 105 o C,Ton is above 330 o C)and controllable mechanical properties(tensile strength at 3.3-6.4 MPa,elongation at break at 370-730%,hardness at 52-74 HA,and tensile recovery at 100% deformation is above 85%).The results of POM and WXRD showwd that there are a large number of spherulites with smaller size than HPE in BTPE,and the crystal form is basically consistent with HPE.Atomic force microscopy(AFM)results showed that BTPE has obvious phase separation structure.3.Research on biodegradability of BTPE.Biodegradation experiments of BTPE were carried out in different p H buffer solution,lipase degradation liquids and soil environments respectively,and the effects of different environmental conditions on the degradation performance of BTPE were explored.The results showed that the degradation degree of BTPE in the p H buffer solution was relatively low,the degradation rate was in the order of Vp H=13>Vp H=6.86>Vp H=1.00,and the mass loss ratio in the alkaline degradation solution for 25 days was about 4%.BTPE showed excellent biodegradability in lipase degradation liquids and soil environment,and the degree of degradation could be regulated by the molecular structure,molecular weight and mass ratio of HPE and SPE.The highest mass loss ratio of BTPE was 94% after 15 days of degradation in lipase degradation liquid.After buried in soil for 120 days,the mass loss ratio of the BTPE was more than 55%,and the surface of the sample was corroded seriously.4.Study on cytocompatibility of the BTPE.The cytocompatibility and the cytotoxicity of BTPE were studied by methyl thiazolyl tetrazolium(MTT)colorimetry assay.The results showed that L929 cells could grow and reproduce well in the extract of BTPE,and the relative growth ratio was above 80%.BTPE had no obvious cytotoxicity,and the evaluation results were qualified for the first grade.Therefore,the BTPE not only is one kind of biodegradable green material with excellent performance,but also has good cytocompatibility,which has great potential in the field of biomedical materials.