An investigation of novel approaches in order to provide crosslinked fullyaromatic polyamide chains

Two different, novel approaches to crosslink fully aromatic, rigid-rod aram id chains were studied. First, the new rigid-rod aramid poly[1,4-phenylen-2 ,5-bis(prop-2-ynyloxy)-terephthalamide] with an inherent viscosity of eta(i nh) = 2.74 dL/g was synthesized by low temperature polycondensation of p-ph enylendiamine and 2,5-bis(prop-2-ynyloxy)-terephthaloylchloride. The pendan t alkinyl moieties allowed thermally induced crosslinking at temperatures h igher than 200 degrees C, No weight loss was found due to this treatment, b ut curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insuff icient stability of the polymer chains against degradation when being disso lved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide contain ing pyrimidine moieties, produced by polycondensation of bis-silylated 2,5- diaminoprimidine and terephthaloyl. dichloride, were spun from nematic solu tions. Fibers were crosslinked by complexation with nickel(II)-ions in the swollen state. Both crosslinked and non-crosslinked, otherwise identically processed samples, were characterized by wide-angle X-ray-diffraction (WAXD ) measurements and mechanical tests. A post-spin heat treatment was employe d to improve the low degrees of orientation 1 and crystallinity that the un treated fibers in general showed. The dominating crystal structures of both fiber samples are similar to "Modification II" of the well characterized f ibers from poly(p-phenylene-terephthalamide) (PPTA). The number and size of the morphological; defects in the crosslinked fibers was significantly hig her than in the non-crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was i nvestigated. The values of all mechanical parameters were considerably lowe r in the case of the crosslinked fibers, probably due to the collapse of th e entire supramolecular order and fiber morphology.