Imperfect Crystals of Poly(butylene succinate) Formed at High Supercooling of the Melt

Prior work revealed distinct differences in the X-ray diffraction patterns of poly(butylene succinate) (PBS) melt-crystallized at different temperatures, regarding the number, width, and position of diffraction peaks, detected in isotropic samples. To further evaluate whether the observed differences are caused by a change of the unit cell, or are solely due to different crystal sizes and perfection, X-ray fiber patterns of solid-state oriented PBS are acquired and analyzed. The data reveal that PBS crystallized at high supercooling of the melt at 20 °C contains crystals with enlarged dimensions of the monoclinic unit cell in the cross-chain direction, compared to PBS crystals initially grown at 20 °C and subsequently reorganized at elevated temperature at 100 °C. High-temperature reorganized crystals exhibit a unit cell similar to that formed after direct crystallization of the quiescent melt at the same high temperature, with the latter, however, unable to draw for observing X-ray fiber pattern. The observed changes in the unit cell of PBS when changing the crystallization temperature are discussed in the context of the widely observed crystallization-temperature-induced crystal polymorphism in other polymers.