Preparation Of Degradable Aromatic/Aliphatic Copolyesters With High Methanical Properties

To obtain a biodegradable polymer material with satisfactory thermal properties, higher elongation and modulus of elasticity, a series of biodegradable aliphatic/aromatic copolyesters were synthesized via melt polycondensation. The resulting copolyesters were characterized by proton nuclear magnetic resonance (¹H NMR), differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD), and their melting temperature (T_m), melting heat of fusion (â–³H_m), glass-transition temperature (T_g), and thermal decomposition temperature (T_d) were obtained.In the first, poly (hexylene terephthalate-co-lactide) (PHTL) was synthesized from dimethyl terephthalate (DMT), 1, 6-hexanediol (HDO), and oligo(lactic acid) (OLA) in the presence of titanium (â…£) butoxide. By using the relative integral areas of the dyad peaks in 'H NMR spectrum of copolyesters PHTL, the sequence lengths of the hexylene terephthalate (n_HT) units in the resultant copolyesters were 3.5. Only one T_g and two T_m's were observed for all samples, and were found to go down gradually with increasing of lactide moieties. The PHTL copolyesters exhibited a pronounced hydrolytic degradability, which increased with the content of lactide units. ¹H NMR analysis of the residue left by evaporation of the mother solution after hydrolytic degradation revealed that the degradation products consisted mostly of lactide and hexylene terephthalate blocks.To improve the thermal and mechanical properties of PHTL, 1, 4-cyclohexanedimethanol (CHDM) was introduced into the PHTL copolyester chains. The rigidity, melting temperature (T_m) and thermal decomposition temperature (T_d) of the PHCTL copolyesters increased obviously with increasing content of CHDM. With comparison to the copolyester without CHDM involving, T_m and T_d of the copolyesters with 50/50 of feeding ratio CHDM/HDO increased to 219℃and 383℃from 129℃and 361℃, respectively. Copolyester PHCTL exhibited a pronounced hydrolytic degradability, and the degradation rates of copolyesters were dependent on their hydrophilicity. To further increase the mechanical properties of PHTL, monomer bis(4-methoxycarbonyl phenyl) terephthalate (BMT) was synthesized, and melt polycondensation from DMT, HDO, OLA and BMT in the presence of titanium (â…£) butoxide was adopted. The melting temperature (T_m) of PHBTL copolyesters decreased but glass-transition temperature (T_g) increased with increasing content of BMT. XRD and POM results of PHBTL polymers indicated that all PHBTL polymers were nematic liquid crystalline polymers.