Effect of coagulation conditions on crystal modification of poly(p-phenylene terephthalamide)

Abstract Poly( p ‐phenylene terephthalamide)(PTTA) films were prepared from sulfuric acid solution with various coagulants. X‐ray diffraction and infrared absorption measurements revealed that the crystal structure of the film coagulated with water showed a new crystal modification II, which was different from the one previously reported by Northolt and Tadokoro et al. The latter structure is called here modification I. Modification II coagulated with water from a solution of lower polymer concentration irreversibly transformed to modification I upon annealing, whereas modification II prepared from highly concentrated solution was thermally stable and scarcely transformed to modification I upon annealing. A liquid crystal‐like swollen structure was found in the intermediate stage of the formation of modification II. In this swollen state, x‐ray diffraction revealed that water molecules are included in hydrogen‐bonded planes and the intermolecular spacing along the van der Waals force direction was unaffected by the existence of the water and remained constant throughout the process of regeneration. Both modifications I and II were found to be stable on treatment with boiling solvents. The transformation of the swollen structure to modification I took place in boiling methanol and acetone.