Synthesis And Crystallization Behaviors Of Poly (Ethylene Succinate) And Its Copolyesters

Biodegradable polyesters are ideal candidates to replace the traditional materials to solve environmental pollution due to their excellent biodegradability. Poly(ethylene succinate) (PES) is one of the most promising biodegradable polyesters, which has attracted much attention. In this work, a series of PES-based polyesters were obtained through copolymerization or nanocompositing methods to meet different demands. In addition, the properties of long chain polyesters were investigated in detail.1. Poly(ethylene succinate-co-octamethylene succinate) (PEOS) copolyestersA series of PEOS copolyesters were synthesized through a melt polycondensation method, and the influences of octamethylene succinate (OS) units on the properties of PEOS were studied with various techniques. The crystal structure of PEOS remained unchanged by the incorporation of OS units, and the crystallinity of PEOS became smaller compared with that of PES. During nonisothermal crystallization process, the crystallization of PEOS was retarded with increasing the OS units. During isothermal crystallization process, the crystallization rate of PEOS was slower with increment of OS units and crystallization temperature, while the crystallization mechanism did not change. The equilibrium melting point temperature values of PEOS were smaller than that of PES due to the dillution effect of OS units. Polarized optical microscope observation found that the size of PEOS spherulites became larger with increasing the OS content and crystallization temperature. The spherulitic growth rates of PEOS and PES exhibited a bell shape within the investigated crystallization temperature range. Moreover, the growth rate of PEOS was slower than that of PES at the same crystallization temperature. In addition, PES and PEOS had a crystallization regime II to III transition temperature, which decreased slightly with increase in DS content.2. Poly(ethylene succinate-co-decamethylene succinate) (PEDS) copolyestersA series of PEDS copolyesters with high molecular weight were synthesized through a melt polycondensation method. The crystallization rate of PEDS decreased with increasing decamethylene succinate (DS) units during both nonisothermal and isothermal crystallization processes, while the crystallization mechanism and crystal structure did not change.The spherulitic morphology and growth rates of PES and PEDS were studied, and each sample showed a bell shape for the growth rates regardless of the DS content. Moreover, the growth rate of the samples decreased with increasing DS content at the same crystallization temperature. The elongation at break values of PEDS were improved significantly with the presence of the DS units, while the yield strength and Young's modulus values became smaller compared with those of PES. In addition, the hydrolytic degradation rates of PEDS were slower than that of PES.3. Poly(ethylene succinate-co-13 mol% decamethylene succinate) (PEDS87)/carboxyl-functionalized multiwalled carbon nanotubes (f-MWCNTs) nanocompositesf-MWCNTs were introduced into a novel biodegradable copolyester PEDS87 to prepare the nanocomposites through a solution casting method. It was found that f-MWCNTs distributed homogeneously through the PEDS87 matrix at the f-MWCNTs content of 0.2 wt%, while some aggregations were developed when the f-MWCNTs content increased to 0.5 wt%. The incorporation of f-MWCNTs accelerated the crystallization rate of the PEDS87 matrix in both the nonisothermal and isothermal crystallization processes, regardless of f-MWCNTs contents, while the crystallization mechanism of the PEDS87 matrix remained unchanged in the nanocomposites at different crystallization temperature.The crystal structure and crystallinity of the PEDS87/f-MWCNTs nanocomposites were similar as those of PEDS87. Moreover, the storage modulus of the PEDS87/f-MWCNTs nanocomposites were improved significantly compared with that of PEDS87, whereas the glass transition temperatures were slightly higher than that of PEDS87.4. Poly(octamethylene adipate-co-octamethylene succinate) (POAS) copolyestersA series of POAS copolyesters were synthesized through a melt polycondensation method. The crystal structures and crystallinity were almost the same as those of poly(octamethylene adipate) (POA). During nonisothermal and isothermal crystallization processes, the crystallization of POAS was retarded by OS units, while the crystallization mechanism did not change. The equilibrium melting point temperature values of POAS were reduced with increasing the OS content, with respect to POA. The spherulitc size of POAS increased with increasing OS untis at the same crystallization temperature; moreover, increasing crystallization temperature and the OS content reduced the spherulitic growth rates of POAS, relative to POA.The aim of above researches was not only to study the properties of these polymers, but also to better understand the relationship between the properties and their structures.