Polymorphism in lamellar single crystals of nylon 11

Abstract

The crystal structures of nylon 11 in the form of lamellar single crystal obtained by crystallization from solution was studied and three crystal modifications were found. Lamellar crystals of form I, which were obtained from solution in diols, have a triclinic unit cell and are similar to the α form of nylon 66 and 610. Molecular chains in these lamellae were tilted at an angle of about 41° to the lamellar surface. However, the crystal structure of this form remains to be solved because the x-ray and electron diffraction patterns have only a few reflections. Lamellar crystals of form II were obtained from solution in water containing 5% formic acid. Form II is monoclinic and is very similar to the α form of nylon 6. Unit cell dimensions are as follows: a = 9.75 å, b = 15.0 å (fiber axis), c = 8.02 å, β = 65°. Lamellar crystals of form III were obtained from solution in water and triethyleneglycol. The crystal structure of this form is pseudohexagonal and is very similar to the γ form of nylon 6. Unit cell dimensions are as follows: a = 9.48å, b = 29.4 å (fiber axis), c = 4.51 å, β = 118.5°.