Synthesis And Properties Investigation Of Poly(4-hyderoxybenzoate) And Its Blends With Poly(Trimethylene Terephthalate)

Poly(trimethylene terephthalate) (PTT) is a new industrialized aromatic polyester after PET and PBT, and the research and industrial production have been cosmically carried out on overseas. Besides its outstanding elastic recovery and dyeability, its application as engineering plastic also attracts people’s attention. Unlucky, there is so little research about PTT in domestic especially in engineering plastic field. Thermotropic liquid crystal polymer (TLCP) is a kind of high-performance polymer material, which not only having high modulus and strength, excellent dimensional and thermal stability, chemical and weather resistance, but also a lower coefficient of thermal expansion and line density. So, it has been accepted widespread concern by industry and academia. Poly(p-hydroxybenzoate) (PHBA) is a TLCP with a high crystallinity and high melting temperature, but it can’t be processed by thermoplastic molding because its thermal decomposition temperature is below the melting point. It blends with a lot of thermoplastics (TP) in order to modify the mechanical properties, dimensional stability, heat resistance, flame retardancy and other properties of the materials. In the present study, poly(p-hydroxybenzoate)(PHBA) was synthesized by using the monomer of p-acetoxybenzoic acid (PABA), and some blends was prepared by melt-blending of PTT with PHBA at high temperature in nitrogen. Systematic analysis of their structure and properties were done.The structure and properties characterizations of the PABA and PHBA oligomers were investigated by using the fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (’HNMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), respectively. The results suggest that PABA and PHBA oligomer were synthesized successively. PABA shows the smectic LCD characteristic within a narrow range of the temperature (187-191℃). PHBA oligomer was synthesized by the condensation of three PABA monomers at proper temperature conditions with an average molecular weight of 420. PHBA is a thermotropic liquid crystal with the nematic characteristics, and the schlieren texture with four brushes is observed. The results of1HNMR suggest that esterification didn’t occur between PTT and PHBA under the reaction conditions, and the final product was the mixture of PTT and PHBA. The melting behaviors of PTT/PHBA blends show a recrystallization peak (Trec) in the heating process, indicating that the blends is more likely to undergo a melt-recrystallization process due to the interaction between the PTT and PHBA. Two melting peaks are specified as the melting of the crystals of PHBA (Tm1) and PTT (Tm2) in the curves of B3 and B4. But, in the blend due to the disturbence of the PTT component, the PHBA is difficult to form liquid crystalline phase, so, no transition peak from liquid crystalline phase to isotropic melt is observed. Furthermore, the start crystallization temperature of B1-B4 is all lower than that of the pure PTT.The non-isothermal crystallization kinetics of PTT/PHBA blends were investigated by DSC. The Avrami equation modified by Jeziorny theory was used. The results suggest that the crystallization peak is broadened and the value of the Tcp is shifted to lower temperature with increasing cooling rate. In the same cooling rate, the t1/2 value of the blends is larger than that of pure PTT while the Kc value of the blends is lower than that of pure PTT. It indicates that the crystallization rate of the blend is decreased when the PTT was blended with PHBA. Effective activation energy was calculated by the differential isoconversional method developed by Friedman. It concludes that the samples are difficult to crystallize when the PHBA adds to the blends.The crystal morphology of the blends is typical spherulites with the Maltese cross-extinction and clearly boundary between eath other. Interesting, transcrystalline morphology appeared clearly in the sample of B1. However, due to the blending effect, the PTT molecules chains restricted the mobility of PHBA, which leading to the change of PHBA phase pattern without nemetic LC. Thermal stability of the blends was studied by using thermogravimetry analysis (TGA) in nitrogen, and the results indicate that the PTT/PHBA blend have better thermal stability than pure PTT.