Formation of spherulitic structure in polyhexamethylene adipamide (66 nylon). I. Structure and optical properties of spherulites at room temperature

It is found in studies with the polarizing microscope that 66 nylon spherulites form readily at temperatures near the melting point and grow until they are stopped by the presence of other spherulites. They possess a radially positive birefringence of approximately 0.01. X‐ray diffraction studies confirm conclusions, drawn from the birefringence results, that the polymer chains are oriented approximately in the tangential plane and that the hydrogen bonds are oriented approximately along the radii. Spherulites are composed of the same type of crystallites as nonspherulitic, crystalline regions of the polymer. The formation of the “transcrystalline” region on the surface of the polymer in the temperature range where spherulites form has been observed at the interface between nylon and a wide variety of other substances. This is taken as evidence that spherulite nuclei form more readily on the surface than inside of the polymer. It is decided, on the basis of x‐ray melting point studies, that the true thermodynamic melting point of 66 nylon must be higher than the normally accepted fusion temperature. From the shapes of interfaces between spherulites, it is concluded that the radial growth rate is constant for any isotherm.