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

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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