Comparison of lamellar crystal structure and morphology of nylon 46 and nylon 5

A comparative study of the crystal structure of lamellar crystals of the isomeric nylons 46 and 5 was carried out. A lattice made of hydrogen-bonded sheets with chains in fully extended conformation and hydrogen bonds in the normal scheme was proposed for the two nylons according to the great similarities in morphology and diffraction data observed for their solution grown crystals. Energy calculations and modeling simulations showed that a model consisting of a statistical arrangement of progressive and alternating intersheet shearing is the most appropriate and consistent to describe the structure of both nylons. A preliminary investigation on the possibility of cocrystallizing nylon 46 and nylon 5 was undertaken. First experimental results were found to be compatible with the occurrence of cocrystallization. Molecular mechanics calculations indicated that insertion of one nylon in the crystal lattice of the other is energetically disfavored. However, cocrystals would be acceptable if they were made of homogeneous blocks of each nylon comprised of about 10 or more hydrogen-bonded sheets. (C) 2000 Published by Elsevier Science Ltd.