Deformation mechanisms of isotactic poly(1‐butene)

The deformation of thin films of poly(1‐butene) (PB) occurs by micronecking. In both fresh (From II crystal structure) and aged (Form I) films finite blocks are drawn off the edge of the microneck, the detailed mechanisms depending on the orientation of the original crystalline ribbons comprising the spherulites with respect to the draw direction. Deformation of fresh thick and thin PB films is accompanied by a transformation to a Form I which melts ca. 5°C lower than that obtained by aging alone (124 vs. 129°C); in thick films the molecular axes in the Form I crystals are oriented in a cone at about 30° to the draw direction until deformation is nearly complete, after which they align in the draw direction. Tensile properties depend on the crystal form, fresh samples having a considerably lower modulus and higher elongation to failure.