Study On The Structure And Property Of Novel Aromatic Polyesters

In this work, the relation between the structure and property of two novel aromatic polyesters, i.e. PTT and PMT was studied by using DSC and FTIR measurements. A comparison of the observed results with that of the traditional aromatic polyesters PET and PBT was made.The isothermal crystallization kinetics of PET, PTT and PBT was studied using a differential scanning calorimeter. Avrami equation was used to analyze the DSC data, and the results indicate that the Avrami constants n of three polyesters are between 2.0 and 2.8. In the experimental region selected in this study, the crystallization rate constant K decreases and crystallization half-time t1/2 increases with increasing crystallization temperature. At the same undercooling degree(ΔT), the crystallization capability of the three polyesters increase in a sequence of PET, PTT and PBT.The isothermal crystallization kinetics of an unique polyester---PMT was also studied. The results show that the Avrami constant n of PMT is located between 2.4 and 2.6. In the experimental temperature range, it was also found that the crystallization rate constant K decrease and crystallization half-time t1/2 increase with the enhancement of crystallization temperature. The melting point of PMT is similar to that of PET and is much higher than that of PTT and PBT, which is in accordance with their chemical structure.Infrared spectra of the non-isothermal annealed PTT film were measured to examine the structural changes during the annealing process. At the higher annealing temperature, the crystalline structure is found in the film as indicated by the appearance of the crystalline bands. Some bands associated with trans or gauche conformation intensified or weakened with increased temperature, indicating that the conformation of propandiol segments (-O-CH2-CH2-CH2-O-) in the polymer chain changes after crystallization—the inner two C-C-C bonds conversed from trans to gauche, while the outer two C-O bonds conversed from gauche to trans conformation.