Synthesis, structure and crystal morphology of nylon 16

The new polyamide nylon 16 was produced by polycondensation of 16-aminohexadecanoic acid in bulk at 210°C. The monomer was obtained by ring-opening hydrolysis of 2-azacycloheptadecanone which was prepared from commercial 8-cyclohexadecen-1-one through a four-step synthesis route. The polymer has a molecular weight of 13 000 and melts at 164 °C. Fiber X-ray diffraction and single crystal electron diffraction measurements revealed that nylon 16 crystallizes in a monoclinic lattice with the parameters a = 0.483 nm, b = 0.935 nm, c = 4.16 nm (chain axis), γ= 121° containing two chains in the unit cell. The packing for the chains was found to be similar to that described for the γ-form characteristic of nylons, whereas a crystal phase in the α-form was not observed. Lamellar crystals of nylon 16 grown in 2-octanol were examined by electron microscopy, and their structure and morphology is discussed in relation to the crystal model conventionally accepted for the γ-form of nylons.