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

A series of novel wholly aromatic copolyamides, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-bis(allyloxy)terephthalamide] (APPTA-x, x (=0, 5, 25, 50, 60, 75, 90, and 100) represents the molar fraction of allyloxy containing structure unit), were prepared via low temperature solution copolycondensation of p-phenylenediamine, terephthaloyl chloride, and 2,5-bis(allyloxy)terephthaloyl chloride. They were converted to the target copolymers, poly(p-phenylene terephthalamide)-ran-poly[p-phenylene 2,5-diallyl-3,6-dihydroxyterephthalamide] (CRPPTA-x), through Claisen rearrangement reaction, as characterized by a comprehensive analyses of NMR, FT-IR, gel permeation chromatography, and differential scanning calorimetry. Although APPTA-x had a poor solubility in common organic solvents, the rearranged products with high co-unit contents, that is, CRPPTA-60, 75, 90, and 100, were readily dissolved in m-cresol, DMF, DMAc, DMSO, and NMP. The effect of these four polymers, used as sizing agents, on the interfacial adhesion between Kevlar fiber and epoxy resin was investigated by the contact angle method, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and microbond tests. Compared with the naked fibers, the sized fibers displayed enhanced surface energy and roughness. The fibers sized with 0.5 wt % CRPPTA-60 solution in NMP exhibited a maximum increase of 19% in interfacial shear strength.