环状低聚酯CBT聚合产物结晶形态与力学性能的调控研究

Cyclic butylene terephthalate oligomers (CBT) is a new prepolymer resin for thermoplastic composites fabrication, which is characterized by "water-like" melt viscosity and can polymerize into high-molecule-weight poly(butylene terephthalate) (PBT) by ring-opening polymerization (ROP). According to the applicant's observation about multifarious crystals' morphologies of polymerized CBT (pCBT) and the related problems between crystals' morphologies and mechanical properties, firstly, the relationship between ROP of CBT and crystallization of pCBT will be systemically investigated, in this case, polymerization and crystallization can be divided into three categories: crystallization during polymerization, polymerization is followed in succession by crystallization, only polymerization but crystallizing during cooling. Moreover, the fine structure, evolution mechanism and tuning methods of different crystal morphologies in multi-level aggregation structure including nucleation, lamellae, spherulites and transcrystallization induced by reinforced fibers will be explored and discussed in depth. On the basis of the former results,the tuning methods of crystal morphologies and mechanical properties of pCBT from the above-mentioned three paths will be studied. The dependant relationships among processing parameters, morphologies tuning,crystal evolution and mechanical properties will be established. Finally, the composites reinforced by continuous fiber will be designed and prepared. Furthermore, the crystallization induced by reinforced fiber (including single fiber and fiber fabric) will be investigated by experiment and finite element analyzing and calculating.The implementation of the project will not only possibly develop the crystalline theory of crystallization during polymerization, lay a foundation for the intensive studies of crystallizaiton morphologies of PBT, widen the understanding of structure and properties based on the cyclic oligomers' ROP, but also provide basic experimental results and scientific evidences for CBT and other cyclic aryl-oligomers' materials design, composites preparation and practical application.

环状对苯二甲酸丁二酯低聚物(CBT)具有超低的熔体黏度，聚合可得聚对苯二甲酸丁二酯(PBT)，在热塑性复合材料领域具有重要意义。针对申请人前期实验观察到的CBT聚合产物多样化的结晶形态及其与力学性能等相关研究的不足，项目拟以CBT在"边聚合边结晶，先聚合后结晶，只聚合冷却时结晶"三类过程中聚合与产物结晶关系的研究为基础，以产物结晶的微观结构、演化机理的研究为桥梁，通过对工艺参数的选择，进行三类过程中结晶形态和材料力学性能的调控研究，建立三类过程中"工艺参数-形态调控-晶体演化-力学性能"之间的联系；最后，设计制备基于CBT的连续纤维增强复合材料，并通过有限元分析，研究增强纤维表面诱导结晶对力学性能的影响规律。项目的实施将为CBT边聚合边结晶的机理研究奠定基础，为PBT结晶形态学的研究提供新的途径，并为基于CBT和其它环状芳香基低聚物开环聚合的材料结构与性能关系的研究提供实验及理论依据。

CBT 是聚对苯二甲酸丁二醇酯（PBT）解聚并环化的产物，是一种由不同含量的环状二聚体到七聚体组成的环状低聚物的混合物。CBT 熔程 120-180 °C，熔体黏度低（20-30 mPa∙s，190 °C），熔融后可迅速浸润各类增强纤维，目前主要用于热塑性复合材料领域。加入催化剂，CBT 可在低于产物熔点（225 °C）的温度下开环聚合得到高分子量的 PBT，反应时间可控制在几十秒至几十分钟，无副产物释放，无聚合反应热，可快速成型，CBT 几乎适用于所有的热固性及热塑性树脂的加工方式。. 项目以 CBT 在“边聚合边结晶，先聚合后结晶，只聚合冷却时结晶”三类过程中聚合与产物结晶关系的研究为基础，获得了相对准确的 CBT 聚合与 pCBT 结晶的温度阈值：即当聚合温度在190-204 ºC时，CBT聚合与pCBT结晶同时发生；当聚合温度在204-212 ºC时，聚合为主，结晶变慢，等温阶段及冷却时都结晶；当聚合温度在212-220 ºC时，聚合先发生，延长时间或冷却时结晶；当聚合温度大于220 ºC时，只聚合不结晶，仅冷却时结晶；随后，进行了等温结晶动力学研究，结果表明：Avrami指数n值介于2.45～2.60之间，并对其等温结晶动力学参数拟合前后的数据作了对比并计算了相对误差，认为拟合前后的n值在合理的误差范围内。pCBT等温结晶时为异相成核，等温结晶活化能为-281.33 kJ/mol，平衡熔点为244.22℃，成核常数为0.3437×10^5K，并计算了折叠链表面自由能。第三，通过对工艺参数的选择，揭示了“边聚合边结晶，先聚合后结晶，只聚合冷却时结晶”三类过程中 pCBT 球晶的演化过程符合经典的研究结果，依次经过成核、超支化、捆束状聚集以及最后的球晶形貌，并通过结晶条件的演化调控方法，研究了琥珀样3D形貌的球晶演化及形成机理；在此过程中，研究了球晶形成过程中的平动及旋转。最后，研究了增强纤维表面诱导结晶行为。. 项目的实施将为 CBT 边聚合边结晶的机理研究奠定基础，为 PBT 结晶形态学的研究提供新的途径，并为基于 CBT 和其它环状芳香基低聚物开环聚合的材料结晶形态的演变、结构与性能关系的研究提供了实验及理论依据。