Study On PET Copolymers Containing Rigid Segments

With the discovery of the liquid crystalline copolyester (PET/PHB) and the successful production of the high modulus and low shrinkage (HMLS) fiber, PET modifications are paid more attention. In the paper, a new method to prepare PET copolymers was explored, by which PET copolyesters with low cost and favorable properties and easily to be industrialized could be obtained.In the paper, we mainly focused on the research about the synthesis of the PET copolymer containing the specified rigid segments and their spinnability. The thesis is divided to three parts as follows:1) Synthesis of the third monomer used for the modification of PET and its characterization.The third monomer used in the preparation of PET copolymers was synthesized by the melt trans-esterification of dimethyl terephthalate (DMT) and p-hydroxyl benzoic acid (PHB). The structure of the synthesized monomer was studied by Fourier transform infrared spectroscopy (FTIR) and ~1H nuclear magnetic resonance spectroscopy (~1H NMR). The results showed that the third monomer was a mixture containing two or three benzene rings. 2) Preparation of PET copolymers and its characterization.PET copolymers with different content of the third monomer were prepared through PTA route. Non-isothermal crystallization and isothermal crystallization differential scanning calorimetry (DSC) showed the melting point and the crystallizing point were lower than that of pure PET, and its crystallization rate was slowed. The crystallization mechanism of the copolymers was similar with pure PET. Polarized optical microscopy (POM) images indicated that the PET copolymer formed spherocrystals at the testing temperature.3) Study on the spinnability of PET copolymers.The melt spinning of PET copolymer was carried out, indicating its good melt spmnablity. The mechanical properties of PET copolymer fiber with low third monomer content (0.5%, 2.0%) was lower than that of pure PET fiber with an intrinsic viscosity [η] of 1.0. But the mechanical properties of PET copolymer containing 4.0% third monomer were similar with the pure PET. Owing to the incorporation of the third monomer, the orientation factor of PET copolymer fiber was decreased revealed by sound velocity measurement. XRD spectra showed the crystalline structure of copolymer fibers was a little different from the pure PET fiber. Moreover, the thermal shrinkage of the copolyester fiber with 4.0% third monomer was much closer to that of pure PET fiber, which indicated that the amount of the third monomer was important for modified PET copolymers.