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PTT及其共聚酯的合成与结晶行为研究
The Study of Synthesis and Crystallization Behavior of PTT and Its Copolyesters
【作者】 徐勇；
【作者基本信息】 浙江大学 ， 高分子化学与物理， 2005， 博士
【摘要】 本文通过直接酯化—缩聚反应路线合成了不同分子量的聚对苯二甲酸丙二醇酯（PTT）;聚对苯二甲酸（丙二醇/乙二醇）酯共聚物（PTET）、聚（对苯二甲酸/间苯二甲酸）丙二醇酯共聚物（PTIT）和聚对苯二甲酸丙二醇酯/聚乙二醇共聚物（PTT—PEG）。采用NMR分析了共聚物的组成和序列分布,采用DSC、DLI（解偏振光强度法）、X射线衍射、偏光显微镜和场发射扫描电镜等研究了它们的结晶行为。并提出了一个新的聚合物等温结晶动力学模型。 研究了酯化、缩聚工艺对PTT合成反应的影响,并着重讨论了各种催化剂在PTT合成中的作用和催化活性,发现在酯化反应中,催化剂的活性遵循下面的顺序:钛酸丁酯>醋酸锌>辛酸亚锡>醋酸钴≥醋酸锰>醋酸锑≥三氧化二锑。缩聚反应中催化剂的活性顺序与酯化时相似:钛酸丁酯>醋酸锌>辛酸亚锡>醋酸钴>醋酸锑。催化剂的中金属原子的电负性是影响催化剂活性的重要因素。使用钛酸丁酯为主的组合催化剂可以得到高分子量的PTT及其共聚酯。 在PTET合成的过程中,1,3PDO单元在共聚物中的实际含量总大于反应起始投料时的含量,而EG的情况则正好相反。合成的PTET共聚酯和PTIT共聚酯都是典型的无规共聚物。采用组合催化剂合成了具有较高特性粘度的PTT—PEG系列共聚酯,利用13C NMR确定了共聚物组成并分析了序列结构,最终得到的产物是以PEG为软段、PTT单元为硬段的嵌段共聚酯,这些共聚酯是由硬段封端的。 通过DSC、WAXD等手段研究PTT在中低过冷区的结晶行为时发现:在177～207℃范围内结晶时,半结晶期随结晶温度的升高而增大,结晶速率常数则相应降低,表明结晶主要受成核能力控制;更高的温度有利于结晶的完善。Avrami指数是介于2.5～3左右的分数,结晶机制是按照异相成核并伴随着三维球晶生长的机理进行的,球晶生长的机理得到了形貌研究的证实。分子链中的催化剂残基起到了异相成核点的作用。结晶过程中不成熟球晶的存在及试样表面球晶不能充分生长可能导致了Avrami指数的下降。 首次采用DLI法测定了PTT在高过冷度下（Tc≤172℃,△T≥75℃）快速结
【Abstract】 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.