Evolution of Crystal Orientation in One-Dimensionally Confined Space Templated by Lamellae-Forming Block Copolymers

Polymer crystallites may exhibit preferred orientation when the crystallization is allowed to occur under the influence of spatial confinement. Using time-resolved wide-angle X-ray scattering (WAXS), we explore the time evolution of the preferred crystal orientation within one-dimensionally confined space constructed by the lamellar microdomains of two crystalline block copolymers, polyethylene-block-poly(DL-lactide) (PE-b-PDLLA) and poly(L-lactide)-block-polyethylene (PLLA-b-PE), where the developments of the parallel and the perpendicular orientation of PE and PLLA crystallites, respectively, were monitored from the early stage of crystallization. Both types of crystallites were randomly oriented at the early stage of formation. As crystallization proceeded further, the ensemble-average orientation progressively improved toward the preferred orientation type, and the rate of establishing the orientation exhibited the same dependence on crystallization temperature (T_c) as the crystallization kinetics. Further examination of the effectiveness of enhancing the average orientation with respect to the increase of crystallinity supported the postulate that the perpendicular orientation of PLLA crystallites arises from the tendency to attain long-range crystal growth, while the parallel crystal orientation of PE is driven by the excluded volume interaction between the crystallites as a result of the intrinsically high nucleating power of PE. (Figure Presented).