The spherulitic structure of crystalline polymers. Part II. The problem of molecular orientation in polymer spherulites

Abstract

The orientation of the crystallites in spherulites was investigated by using special microbeam x‐ray techniques. The materials studied were: polyhexamethylene adipamide and sebacamide, polyethylene, and polyethylene terephthalate. In all these substances the c axes (molecular chains) were perpendicular to the radii of the spherulites, with some deviation from strict perpendicularity in the case of polyethylene terephthalate. The particular orientation of the crystallites around their c axes was in full agreement with the observed sign of birefringence, in the positive and negative polyamide spherulites, in polyethylene (where the indirect deduction made in earlier works has also been confirmed), and in the negative spherulites of polyethylene terephthalate. In the positive polyethylene terephthalate spherulites, while a fit between x‐ray results and birefringence might still be possible, it is somewhat doubtful whether the sign of birefringence could be accounted for by the crystallite orientation alone. The possible arrangements of the crystallites is discussed and it is suggested that the picture of closely coiled helices with the molecules lying along the winding direction might offer the most satisfactory explanation.