杂环芳香族聚酰胺是在对位芳纶树脂聚对苯二甲酰对苯二胺聚合过程中加入2-(4-氨基苯基)-5-氨基苯并咪唑作为第三单体得到的共聚物，将其聚合液经过湿法纺丝可以得到高强纤维共聚杂环芳纶（简称共聚芳纶）。共聚芳纶具有优异的力学性能、优异的热稳定性以及化学稳定性等特性。在诸多对力学性能和耐热性能要求较高的应用领域，有不可或缺的应用价值。然而加入了第三单体得到共聚芳纶的聚合情况，无论是从聚合时间、聚合反应程度以及聚合相变过程上都和对位芳纶的聚合情况有着非常大的差别。虽然目前国内有着生产共聚芳纶的生产线，但是其聚合和纺丝工艺过于复杂，生产效率低，年产量较小，与上世纪苏联的产量相比仍有较大差距，并且国内技术对其内在原理的研究还不够深入。故本课题深入研究了以N，N-二甲基乙酰胺为溶剂，氯化锂为助溶剂的共聚芳纶聚合体系，首先研究了助溶剂和单体溶解度之间的关系，发现二者正相关。之后对聚合进行了系统研究，包括助溶剂浓度、单体浓度、第三单体所占比例、加料次数以及加料方法等众多因素对聚合的影响规律，分析了所得聚合液的动态黏度、比浓对数黏度和上述变量之间以及这二者之间的关系，发现动态黏度和比浓对数黏度变化趋势一致，而单体浓度和第三单体所占比例对二者影响较大。目前公开报道的共聚芳纶聚合体系因为其单体浓度偏低，聚合反应需要较长（>45分钟）时间，反应时间太长导致无法采用连续聚合工艺，只能依靠釜式聚合。但是共聚芳纶的聚合不太稳定，间歇釜式聚合很难保证聚合稳定性，而且生产效率低下。故本文为了解决这一问题，研究了高浓度下的共聚芳纶聚合情况，测定了不同的聚合条件下聚合液的旋转黏度，以及不同温度下的旋转黏度，尝试了将高浓度聚合液再次溶解，是否能降低其旋转黏度以符合工业生产标准。同时尝试了能否在聚合过程中额外加入对苯二甲酰氯是否能及时使分子链封端，控制住旋转黏度不至于过高，为未来的工业生产提供了一种新思路。
Heterocyclic aromatic polyamides are copolymers produced in the polymerization of poly-p-phenylene terephthamide para-aramid resin by adding 2-(4-aminophenyl)-5-aminobenzimidazole as the third monomer, i.e., copolymer aramid fibers. Heterocyclic aramid, a type of high strength fiber, can be produced with wet spinning of heterocyclic aromatic polyamide solution. These high strength fibers produced have excellent mechanical properties, thermal stability, chemical stability, etc. Heterocyclic aramid fibers have significant value in application of areas which have strict requirements for mechanical properties and heat resistance.However, there is notable differences in reaction time, severity, and phenomenon between the co-polymerization of aramid with a third monomer and polymerization of aramids. Although there are copolymer aramid fiber production lines in China, the production flow is overly complicated with low efficiency and small annual yield, where there is still a noticeable gap with the yield from the Soviet Union in the last century. Also, the underlying theories were not thoroughly studies before applying techniques from the Soviet Union into production. This research studied the copolymerization system of aramids with N,N-dimethylacetamide as solvent and lithium chloride and cosolvent. First, the relationship between concentration of cosolvent and monomer solubility was studied, and they turned out to have a positive correlation. Then, a series of systematic polymerization experiments were performed to understand the effects of cosolvent concentration, monomer concentration, ratio of the third monomer, reactant additions, and method of reactant additions, and to analyze the dynamic viscosity, inherent viscosity, and the relationship of the above two properties of the produced polymer solution. It was found that dynamic viscosity and inherent viscosity tended to change consistently, while monomer concentration and ratio of the third monomer are affecting the two properties significantly.Existing techniques require at least 45 minutes of aramid copolymerization due to low concentration of monomers. The length of reaction time made it unsuitable for a continuous polymerization process flow, and had to rely on polymerization kettles. However, copolymerization of aramid is unstable, and the kettle must be cleaned before the next reaction to start, otherwise the subsequent reaction in the kettle will result in an absolute failure; even with cleaning after every reaction, each kettle polymerization may produce polymers with varying quality, resulting in a low productivity due to defectives falling below the application standard. To solve this limitation, this research has studied copolymerization of aramid under high concentrations. Rotational viscosity of polymer solution was measured under different polymerization conditions and different temperatures, and re-dissolve of the high concentration polymer solution was experimented to reduce the rotational viscosity in order to meet the industry production standard. The addition of terephthaloyl chloride to end-cap polymer chain during co-polymerization process was also studied, which may help control the rotational viscosity to stop growing higher, and providing an innovative ides of increasing production capacity in the future.
