Studies on high-performance wholly aromatic polyamide fibers by means of molecular design

1. 为实现高性能的对芳纶纤维，设计并实现了包括吡嗪环在内的二苯环或对苯环组成的新型芳纶，以取代聚对苯基对苯二甲酸（PPTA）。该聚合物可溶于硫酸并形成液晶。试验了两种合成方案：一种是以对氰苯酮为原料，经溴化、二聚、水解得到terphenyl单体2,5-双（4-羧基苯基）吡嗪；另一种是合成联苯单体2-(carboxhenvl)-5- carboxphenyl -5- aminopyrazine。这些单体在N-甲基吡咯烷酮和氯化钙的溶剂中与对苯二胺缩聚。以2,5-双（4-羧基苯基）吡嗪为原料制备的terphenyl型对芳纶的特性粘度为2.01 dL/g， 10%时的失重温度为545偶联温度。根据相图，该聚合物可溶于纯硫酸中，形成约8%以上的液态结晶。但与PPTA相比，液晶范围较窄，易结晶，导致纤维纺丝困难。从取向的terphenyl芳纶薄膜得到的x射线结构估计其模量为310 GPa，约为PPTA的1.6倍。这种评价与分子设计的期望是一致的。为改善联苯型芳纶结晶速度快、液晶弛豫快的缺点，合成了两种联苯型芳纶单体。与现有的芳纶相比，多苯基芳纶的模量有所提高，但加工难度很大。增加吡嗪环在单体单元中的比例，使液晶相比PPTA更稳定，有利于纺丝。合成了两种类型的芳纶单体，但产率很低，目前还不能很好地评价聚合物作为纤维的性能。少

1. For the purpose of realization of high-performance para-aramid fibers, in place of poly(p-phenylene terephthalamide)(PPTA), novel aramids composed of di- or ter-phenylene rings including pyrazine ring were molecular-designed and realized. The polymers were soluble in sulfuric acid and formed liquid-crystal.2. Both schemes of syntheses were tried: one is use of p-cyanoacetophenone as starting material, which was brominated, dimerized and hydrolysed to obtain terphenyl monomer, 2,5-bis(4-carboxyphenyl)pyrazine, and the other is to synthesize biphenyl monomers, 2-(carboxvDhenvl)-5-carboxypyrazine or 2-(carboxyphenyl)-5- aminopyrazine. These monomers were condensation-polymerized with p-phenylenediamine in a solvent of N- methylpyrrolidone and calcium dichloride.3. The para-aramid of terphenyl type, using 2,5-bis(4-carboxyphenyl)pyrazine was 2.01 dL/g of intrinsic viscosity and its weight loss temperature at 10% was 545ﾟC. The polymer was soluble in pure sulfuric acid and formed liquid- … More crystal above ca 8 % according to the phase diagram. The range of liquid crystal is, however, narrower compared with that of PPTA and easily crystallized, which resulted in the difficulties of spinning of fibers. From the X-ray structure obtained from the oriented thin film of terphenyl aramid the modulus was evaluated 310 GPa which amounts to about 1.6 times that of the PPTA. This evaluation is along with the expectation of molecular design. To improve the faults of fast crystallization rate and rapid relaxation of liquid crystal of terphenyl type aramid, two kinds of monomers of biphenyl type aramids were synthesized.4. Multiphenyl aramid was found to improve modulus compared with the existing aramids but its processabilty was extremely difficult. The increase of the fraction of pyrazine ring in the monomeric unit brings more stable liquid trystal phase than PPTA, which enables easy spinning. Two types of such aramid monomers were synthesized but the very low yield did not allow satisfactory evaluation of polymer properties as fiber at present. Less