Single Crystals of Chain-Folded Copolyterephthalamides

Abstract

Crystallization of copolyaramides composed of rigid poly(p-phenylene terephthalamide) segments (containing 3−11 aromatic cycles) and short amine aliphatic chains (5−10 CH2 groups) was studied. Crystallization was induced at room temperature by slow saturation with methanol vapors of sulfuric acid solutions. In electron diffraction, the 3AR6DA, which has monodisperse rigid blocks, exhibits weak but typical single crystal diffraction, with relatively sharp diffraction spots. Other wARnDAs, for which the rigid blocks are polydisperse, show a similar diffraction diagram albeit with lower resolution and considerable peak broadening, indicating that considerable disruption of the crystal phase has taken place. All observed diagrams correspond to the hk0 level, and chains are perpendicular to the lamellar plane. Atomic force microscopy observations show that most crystals are multilamellar, the thickness of each lamella increasing regularly with the number of aromatic groups in the rigid segment. The average lamellar thickness value is in agreement with the expected rigid segment length. It is therefore concluded that the addition of a short aliphatic chain fragment allows chain folding to occur.