Effect of structure on light transmission in isotactic polypropylene and random propylene-1-butene copolymers

The structure of semi-crystalline isotactic polypropylene and random isotactic copolymers of propylene and 1-butene at the nanometer and micrometer scales is controlled by the pathway of melt-crystallization, and the concentration of chain defects. Rapid cooling of the melt results in formation of mesomorphic nodules, being not organized in a higher order superstructure. Slow melt-crystallization, in contrast, allows formation of lamellae. These lamellae arrange within spherulites of a size which is decreased in copolymers. Analysis of the light transmission reveals a distinctly higher transparency in non-spherulitic preparations. Spherulitic samples exhibit a lower transparency, increasing with decreasing size of spherulites. Annealing of quenched preparations at elevated temperature leads to an increase of the crystallinity and of the dimensions of crystals, without affecting their habit, and their higher order organization. The transparency is only slightly decreased in these specimens. It can be demonstrated that samples of largely different transparency but identical crystallinity can be generated without the use of optical clarifiers/nucleation agents.