杂环芳纶溶液中预有序结构调控及其纤维制备研究

The typical heterocyclic aramid is one kind of aromatic copolyamide containing benzimidazole structure in the main chain. Heterocyclic aramid fiber shows high mechanical properties and composite performance, which has been gradually applied to the field of national defense industry. However, the currently industrialized heterocyclic aramid is spun from isotropic solution and the obtained as-spun fibers shows the amorphous structure with low orientation, which leads to low degree of crystallinity in heterocyclic aramid fiber after heat treatment. In this study, the idea of formation of pre-order structure in heterocyclic aramid polymer solution and the corresponding intervention of new spinning method are used to improve the crystallinity and orientation, and thus further improve the mechanical properties of heterocyclic aramid fiber. Firstly, based on the different reactivity of head and tail amino groups of 5 (6)-amino-2- (4-aminobenzene) benzimidazole (PABZ) and solubility difference of PABZ in different conditions, sequential structures in heterocyclic aramid will be controlled in order to increase chain rigidity. Secondly, the benzimidazole units in heterocyclic aramid can be complexed with different kinds of Lewis acids and corresponding polyelectrolyte effect will be controlled and studied. The isotropic-namatic phase transition and pre-ordering solution can be achieved through the construction of ordered structure of chain sequence and the control of electrostatic interaction in polyelectrolytes. Finally, the pre-ordered structure in heterocyclic aramid polymer solution can be further improved by the flow field in the spinning process. And the pre-ordered structure can be "freezed" by gel-spinning and the gel spinning method will be established for preparation of heterocyclic aramid fiber for the first time. This related research results will establish a theoretical and technical foundation for the preparation of a new generation of high-performance heterocyclic aramid fibers.

本项目针对目前已经工业化的杂环芳纶聚合物原液纺丝工艺（在有机溶剂中聚合后直接纺丝）难以制得高有序程度杂环芳纶的问题，首先利用5(6)-氨基-2-(4-氨基苯)苯并咪唑单体（PABZ）两端氨基的活性差异和PABZ在不同条件下的溶解性差异合成序列有序的杂环芳纶聚合物，以增加链刚性；其次将该聚合物络合路易斯酸并调控相应的聚电解质效应，通过链序列有序结构的构建以及利用聚电解质中的静电相互作用来实现isotropic-namatic相转变和溶液预有序结构的调控；最后通过纺丝成型中的流动场进一步增加杂环芳纶聚合物溶液中的预有序结构，并采用凝胶纺丝工艺“冻结”预有序结构，初步建立凝胶纺丝方法在杂环芳纶制备中的新应用。本研究通过杂环芳纶溶液预有序结构的调控和相应纺丝新方法的介入以提高纤维的结晶度和取向度，进而提高后期杂环芳纶的力学性能。其相关研究成果可为制备新一代高性能杂环芳纶奠定理论和技术基础。

杂环芳纶具有优异的力学性能和复合性能，现已逐渐被应用于国防军工领域。但作为先进树脂基复合材料用增强介质，其力学性能依然有待进一步提高。杂环芳纶聚合物的纺丝溶液为各向同性，所制备的杂环芳纶原丝有序程度较低，从而限制了后期成品丝力学性能的进一步提升。本项目以国家重大需求为导向，立足于杂环芳纶溶液性质及其构筑的预有序结构，并依据研究计划和研究目标，开展的主要研究内容：①序列有序结构杂环芳纶聚合物的合成及结构；②杂环芳纶溶液性质及路易斯酸碱相互作用对其有序结构的影响；③调控杂环芳纶松弛时间提高其纤维取向度及力学性能的研究；④提高杂环芳纶有序程度的成型加工新方法及新原理。通过上述研究，建立了杂环芳纶头/尾序列有序结构合成方法；明晰了杂环芳纶稀溶液的基本性质及链结构参数；发现了升温促使杂环芳纶凝胶化转变行为；结合流变、分子模拟、升温红外等阐释了凝胶化的转变机理，发现苯并咪唑络合HCl形成的独特结构是导致其凝胶化的关键因素，并且凝胶促使大分子链局部规整排列，从而形成了“类液晶”的预有序结构。为此，我们提出了凝胶化自组装制备杂环芳纶薄膜/纤维的新方法，制备的薄膜面内取向度大幅度提高，拉伸强度提高了30%。此外，我们还通过添加高分子量组分调控溶液松弛时间提高了杂环芳纶的取向度和力学性能。这些研究为制备高性能杂环芳纶纤维奠定了新的技术途径和新原理，为更好地的满足国家重大需求奠定了研究基础。在国内外学术期刊上，共发表标注基金号的期刊学术论文11篇（目标：3-5篇），包括第一标注4篇，第二标注7篇，其中以通讯作者身份发表SCI收录论文10篇。申请国家发明专利4项（目标：1-2篇），其中授权国家发明专利3项，项目负责人多次参加国内国际会议，并作邀请报告和口头报告。培养研究生4名，其中硕士毕业生生2名，博士毕业生1名，在读硕士研究生1名。