The Study Of Synthesis And Crystallization Behavior Of PTT And Its Copolyesters

Poly trimethylene terephthalate (PTT) with various molecular weights, poly (ethylene/trimethylene) terephthalate (PTET), poly trimethylene (isophthalate/ terephthalate) (PTIT) and poly trimethylene terephthalate- poly ethylene glycol copolyesters were prepared by polycondensation. The compositions and sequential structures of copolyesters were determined by NMR. The crystallization behavior of these polyesters was studied by DSC,WAXD, DLI(depolarized light intensity), PLM and FE-SEM. It is the first time that PTET and PTIT copolyesters were synthesized.The polymerization conditions were optimized and the activity of catalyst was studied. The activity of catalyst in esterification was as follow: Ti(OBu)₄ >Sn(Ac)₂ > Zn(Ac)₂ > [C₄H₉CH(C₂H₅)COO]₂ > Co(Ac)₂ >Mn(Ac)₂ > Sb(Ac)₃ >Sb₂O₃ . The activity of catalyst in polycondensation was as follow: Ti(0Bu)₄ >Sn(Ac)₂ > Zn(Ac)₂ > [C4H₉CH(C₂H₅)COO]₂ > Co(Ac)₂ > Sb(Ac)₃ . The electronegativity of metal in the catalyst effectively influences the activity of catalyst. To obtain polyesters with high molecular weight, it is essential to use complex catalysts dominated by Ti(OBu)₄ in the preparation.The content of 1,3 PDO unit incorporated into the copolymer is always larger than that fed in the bulk polymerization. All resultant PTET and PTIT copolyesters are typical random copolyesters. It is essential to use a complex catalysts to produce a PTT-PEG copolyesters with a high molecular weight. The resultants in the produce of PTT-PEG copolyesters are block copolyesters in which PTT unit works as hard segment while PEG unit works as soft segment.Crystallization half-time of PTT increased with crystallization temperature while crystallization rate constant decreased with crystallization temperature when PTTcrystallized at the temperature range of 177²07°C. The crystallization process is dominated by nucleation and higher temperature will help to obtain a more perfect crystal. The Avrami exponent n suggested a three-dimensional spherulite growth with athermal nucleation mechanism which was confirmed by morphology study.Crystallization kinetics of PTT at high undercoolings (Tc < 172°C, A T > 75 °C) was presented for the first time by means of depolarized light intensity technique. PTT sample with a viscosity-average molecular weight of 56020 crystallized fastest at 128 °C. It is in the temperature range of 110 150°C that PTT has a high crystallization rate. The crystallization rate of PTT decreased with molecular weight and crystallization activation energy was increased with molecular weight. PTT has a higher crystallization rate than PET at the same undercooling.The development of mathematic models which relate the isothermal crystallization kinetics was reviewed. A new mathematical model was constructed for analysis of polymer crystallization. The crystallzation data of isothermal crystallization of PTT ,PTET,PTIT and PTT-PEG copolyesters fit the model very well.Crystallization behavior of PTT including the secondary crystallization process was analyzed. Secondary crystallization take place markedly when PTT crystallized at high undercooling. In PTT crystallization process, crystallization rate of secondary crystallization process is lower than that of primary crystallization. When PTT crystallized at a higher undercooling, homogeneous nucleation increased. The number of the spherulite also increased with undercooling. In secondary crystallization, crystallization mode shift to low-dimensional crystal growth caused probably by spherulite impingement.The crystallization behavior of PTET copolyesters and PTIT copolyesters was investigated for the first time. In present work, although the PTT copolyesters had high PET contents, their crystallization was still observed. The reason could be attributed to the similar chemical structures of 1,3 PDO and EG However, the results presented in this study proved that only one type of unit is able to crystallize in PTET coplyesters. Poly isophthalate terephthalate(PTI) is a amorphous polyester and the incorporation of TPA caused a poor crystalline polyester. PTIT copolyesters with 40mol % become completely amorphous.The incorporation of TPA and EG as a comonomer reduced the crystallization rate of copolyesters. In comparison to EG, TPA is a comonomer which can destroy the regularity of the chain more efficiently. In the secondary crystallization of PTET and PTIT copolyesters, low-dimensional crystal growth occurred.The crystallization behavior of PTT—PEG copolyesters was presented for the first time. PEG is not able to crystallize by itself or co-crystallize with PTT unit. The incorporation of PEG ( 0 17.78wt % ) can enhance the crystallization temperature(TCh) when the copolyesters crystallized from melt. The crystallization rate can be enhanced by the incorporation of PEG with very low content(2.61 wt%). In secondary crystallization of PTT-PEG copolyesters, crystallization mode also shift to low-dimensional crystal growth. The copolymerization affected the crystallization rate, but had a little influence on crystallization mechanism.