The structure of high polymer spherulites

The spherulitic structures in very thin films of linear plolyethylene and poly‐oxa‐1,4‐bis(dimethylsilylene) benzene have been examined by a variety of optical techniques. These techniques included bright field electron microscopy and bright and dark field light microscopy. Polarization effects in these polymers were also examined using the light microscope. The polarization phenomena were most marked in the poly‐oxa‐1,4‐bis(dimethylsilylene) benzene, presumably as a result of the benzene ring. The negative polyethylene spherulites showed a banded structure in all types of illumination. It was shown that the banded structure exhibited between crossed Nicols is due to low positive birefringence while the black cross was due to zero amplitude effects. All the optical phenomena could be interpreted in terms of a model which proposes that a given spherulite radius is coposed of a stack of crystallites whose refractive index ellipsoids (a) have centers along the radius, ( b ) have optic axes which make a fixed angle with the spherulite radius, and ( c ) are twisted as they go out along the radius so that the displacement is proportional to the twist. The model also emphasizes the presence of interstitial amorphous polymer. On the basis of this model the crystallites in polyethylene spherulites were shown to have a twist length of about 4 μ and to have their major refractive index axes (chain directions) inclined at an angle of 75° to the spherulite radius.