Hydrogen Bonding Induced Co-Ordering and Interfacial Curvature Controlled Crystallization Behavior of Binary Copolymer Blends

We investigated the effects of the hydrogen-bonding interaction and molecular architecture on the phase and crystallization behaviors of binary copolymer blends. In blends comprising polystyrene-block-poly­(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly­(acrylic acid) (PS-b-PAA) block copolymers, the hydrogen bonding between PEO and PAA block chains improved their miscibility so that they shared the common domains and microphase-separated against the domains composed of PS block chains, keeping their junctions at the common interfaces. However, hydrogen bonds reduced the crystallizable chain length of PEO, causing crystallization to occur within a more confined region and at a lower temperature. In the PS-b-PEO and polystyrene-graft-poly­(acrylic acid) (PS-g-PAA) blends, the junctions between the PS main chain and the branched PAA block chains in PS-g-PAA were also localized at the PS-b-PEO interface with the PS main chains segregated into PS microdomains and the PAA branches hydrogen-bonded with the PEO blocks in the other microdomains. The branched structure of PS-g-PAA increased the interfacial curvature more effectively than the linear structure of PS-b-PAA, and subsequently, it induced a morphological transition. This morphological change altered the nucleation mechanism of the PEO block chains from heterogeneous nucleation in lamellae to homogeneous nucleation in cylinders, resulting in a substantial decrease in the crystallization temperature. Furthermore, the hydrogen-bonding interaction suppressed PEO crystallization, thereby decreasing the crystallization rate and degree of crystallinity considerably