Investigation into the morphology of aliphatic segmented block copolymers with controlled thickness of crystals

Abstract

In the present paper, aliphatic thermoelastoplastics, consisting of alternating segments of polytetrahydrofuran and monodisperse segments of glycine and β-alanine bisoxalamides, are studied. Phase transitions and the orientation of crystals are determined by experiments using X-ray structural analysis during the drawing process in situ. Two types of morphology have been revealed. Fibrillar crystals with chains oriented perpendicularly to the drawing direction are formed at low draw ratio values. At high deformation degrees, a fracture of large crystals and a reorientation of polymer chains along the drawing direction are observed. It is shown that the thickness of the hard block crystals is constant and independent of the sample thermal prehistory. The tilting angle of bisoxalamide chains is determined using four-spot small-angle patterns. It turns out that in the case of glycine the tilting angle is rather small (∼5–15°), while for alanine it reaches 24°. The flexible block crystallization during the drawing process at room temperature was found regardless of the block length. The surface free energy of hard block crystals proved to be rather low (∼18 erg/cm2), which is probably due to the entropic contribution from flexible blocks.