Interfacial polycondensation aromatic polyamide fibers

Aromatic polyamide fibers, better known as aramid fibers, have been defined as a long chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings [42] The first significant material of this type was introduced in 1961 by Du Pont as Nomex. It is poly(m-phenyleneisophthalamide), prepared from m-phenylenediamine and isophthaloyl chloride by interfacial polycondensation. 

With a few exceptions, interfacial polycondensation has remained a laboratory method for the synthesis of polymers, since diacyl chlorides are too expensive for commercial production. The exceptions include the polycondensation of bisphenols with phosgene (see Section 26.5.1) and the synthesis of aromatic polyamides, from m-phenylene diamine, isophthaloyl chloride, and terephthaloyl chloride (Section 28.2.4). The method is also used to give wool a fluff-free finish by producing a polycondensate from sebacoyl chloride and hexamethylene diamine on the wool fiber. 

An aromatic polyamide is produced by the interfacial polycondensation method from isophthalyl dichloride (in cyclohexanone) and m-phenyl-ene diamine dihydrochloride with trimethyl amine hydrochloride added as catalyst and NaOH to absorb the HCl. The polymer has a very high melting point of over 375°C and is also of poor solubility. It can be spun out of a boiling dimethyl acetamide solution with the addition of 3% CaCl2. Textiles and fibers cannot be dyed and are used in industry, for example, to reinforce elastomers and as filter cloths for hot gases. Papers are manufactured from fibers that have been cut and then sintered together they have a thickness of 2-30 mil (1 mil = 0.0025 cm) and are used for electrical insulation. 

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