Synthesis and characterization of poly[p-phenylene terephthalamide-co-N,N'-(sulfophenylene)phthalamide]

Poly(p-phenylene terephthalamide) when solution-spun from concentrated H2SO4 into fiber, commercialized by Du Pont under the trade name KevlarRTM, has already been noted for its outstanding thermomechanical properties, especially ultra-high specific tensile modulus and tensile strength even at elevated temperature. When an anisotropic poly(p-phenylene terephthalamide)/H 2SO4 dope is processed into fibers, the polymer molecules will maintain their fully extended conformation and align themselves in the fiber axial direction. Although this accounts for ultra-high specific tensile modulus and tensile strength, it will result in fairly weak associations in the transverse direction due to the lack of entanglements between molecules. In order to enhance these lateral forces without sacrificing the usual properties, a copolymer, poly[p-phenylene terephthalamide-co-N,N '-(sulfo-phenylene)phthalamide] or more simply known as lightly sulfonated poly(p-phenylene terephthalamide), LS-PPTA, is proposed. It is a copolymer with the introduction of a controlled amount of third structure unit, 2,5-diaminobenzene-sulfonic acid, into the major poly(p-phenylene terephthalamide) backbone.;The procedure used for the preparation of LS-PPTA was the low-temperature solution condensation technique developed for poly(p-phenylene terephthalamide) and homologues. Two different solvent systems were used for the polymerization, DMAc with 5% LiCl and HMPA/NMP with a 2/1 volume ratio. The latter is superior in achieving high molecular weight polymer. The resulting polymer shows unique solution properties in HMPA with the presence of LiCl. Among which is the suprastructure of spherulitic aggregation that is believed to be a indirect evidence of ionic interaction from neutralized sulfonic groups. This will open the door for the concept of lateral ionic interactions in a highly orientated solid state and the liquid crystalline ionomer with satisfactory strength transverse to the direction of chain orientation. In addition to this, characterizations of the polymer were carried out for determination of structure and investigation of solution properties.