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

Abstract

Two different, novel approaches to crosslink fully aromatic, rigid‐rod aramid 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 ηinh = 2.74 dL/g was synthesized by low temperature polycondensation of p‐phenylendiamine and 2,5‐bis(prop‐2‐ynyloxy)‐terephthaloylchloride. The pendant alkinyl moieties allowed thermally induced crosslinking at temperatures higher than 200°C. No weight loss was found due to this treatment, but curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insufficient stability of the polymer chains against degradation when being dissolved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide containing pyrimidine moieties, produced by polycondensation of bis‐silylated 2,5‐diaminoprimidine and terephthaloyl dichloride, were spun from nematic solutions. 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 employed to improve the low degrees of orientation and crystallinity that the untreated fibers in general showed. The dominating crystal structures of both fiber samples are similar to “Modification II” of the well characterized fibers from poly(p‐phenylene‐terephthalamide) (PPTA). The number and size of the morphological defects in the crosslinked fibers was significantly higher than in the non‐crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was investigated. The values of all mechanical parameters were considerably lower in the case of the crosslinked fibers, probably due to the collapse of the entire supramolecular order and fiber morphology.

Crosslinked polyamide based on main‐chain type polybenzoxazines derived from a primary amine‐functionalized benzoxazine monomer

“…It is therefore possible that for crosslinked aromatic poly(amide‐benzoxazine), this transition is due to the β‐transition, taking into consideration that even though T g of the current polymer is higher than poly(BA‐a), the presence of an aliphatic segment in the repeating unit makes possible a β‐transition at such a value. Crosslinked aromatic polyamides32–40 have been studied in the past. However, the majority of the studies relate to the reverse osmosis membrane development and either the degradation as a result of crosslinking and permeation properties were of interest.…”

Simple Synthesis of Hydroxyl and Ethylene Functionalized Aromatic Polyamides as Sizing Agents to Improve Adhesion Properties of Aramid Fiber/Vinyl Epoxy Composites

“…The introduction of a sizing agent is reported as an effective way to improve the interfacial adhesion of epoxy/rubber composite materials [ 14 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. It is also proposed as an effective approach to improve the compatibility between aramid fiber and other polymers via introducing various functional groups into an aromatic polyamide [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Wan and co-workers introduced allyl and hydroxyl groups into the aramid fiber surface [ 21 , 22 ], remarkably enhancing the interfacial adhesion between PPTA fibers and epoxy/rubber composites.…”

Synthesis and properties of poly(p-phenylene terephthalamide) bearing both polar and unsaturated substituents introduced via claisen rearrangement reaction

“…Synthesis of PPTA with various substituents through homopolymerization or copolymerization represents another effective approach to improve its compatability with other polymers . For example, the hydroxy group was known to improve the affinity of PPTA toward epoxy, while the propargyl group enhanced interfacial adhesion toward rubber . However, in most cases, one type of functional groups is only effective to one type of polymer matrices.…”