Abstract: The volume of unit cell, the scattering invariant Q, and the crystalline lamellar long period of polycaprolactone in the processes of cooling and heating covering α and β relaxation were studied using X-ray small angle scattering and wide angle diffraction. Experimental results indicate that the behavior of crystalline and amorphous regions is interlinked in the whole process. It was found that the variation of the unit cell volume is reversible. An abrupt variation of the unit cell volume at -90 ℃ was caused by the freeze or activation of the β relaxation of tie molecules, and thus the change of expansion coefficient of the unit cell volume. The variations of scattering invariant Q with temperature are also reversible but having a transition point due to α relaxation. Because of the occurrence of insertion crystallization mode in the amorphous regions in the process of cooling, the temperature required to melt the crystals becomes higher with respect to the crystallization temperature. Therefore, the long period is not fully reversible in the processes of cooling and heating.

Key words: polycaprolactone, expansion of unit cell, long spacing, SAXS, invariant Q