We investigated the competitive effects of the hydrogen-bonding interaction and molecular weight on the phase and crystallization behaviors of polystyrene-block-poly(ethylene oxide) (PS-b-PEO)/polystyrene-block-poly(acrylic acid) (PS-b-PAA) blends. The hydrogen-bonding interaction between PEO and PAA chains improved their miscibility, enabling the distinct block copolymers to co-organize into common PS and PEO/PAA microdomains. When the molecular weight ratio of PS-b-PEO to PS-b-PAA exceeded 4.5, the entropy penalty (caused by long PEO chains organizing into the PEO/PAA microdomains) suppressed the hydrogen-bonding interaction, inducing macrophase separation. Localization of large PS-b-PEO chains and small PS-b-PAA chains at the common interface caused the PEO/PAA microdomains to be composed of coexisting PEO/PAA and PEO regions (Regions I and II, respectively). Hydrogen bonds hampered PEO crystallization in Region I, whereas the PEO in Region II was crystallizable. When the molecular weight ratio of PEO to PAA was decreased, PEO crystallization in Region II became strongly confined, reducing the crystallization temperature and kinetics. Increasing the PS-b-PAA content expanded the separation distance between PEO chains in Region I. Consequently, PEO chains in Region II became more stretched to maintain the microdomain incompressibility, which inhibited PEO crystallization in Region II.

This study examined crystal orientation confined within a lamellar microdomain morphology formed by the blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA) through wide-angle X-ray diffraction. The hydrogen-bonding interaction between PEO and PAA molecules enabled block copolymers to co-organize into a microphase-separated morphology without inducing macrophase separation, but it hampered PEO crystallization. PEO crystallization that occurred at −20 °C resulted in the nucleation mechanism to be dominant, thus leading to the formation of small crystals. Small crystals allowed them to be free from spatial confinement, and they tended to be oriented with their c-axis parallel to the microdomain interface. By contrast, when PEO was crystallized at 40 °C, the high temperature facilitated PEO crystals to exhibit large crystallite sizes, which aligned perpendicularly to the microdomain interface. An increase in the PS-b-PAA concentration considerably reduced the crystallizability of PEO. The presence of a low amount of crystals and additional lateral confinement formed by hydrogen-bonded PEO/PAA reduced the degree of orientation regardless of the crystallization temperature.