Influence of Microphase Morphology and Long-Range Ordering on Foaming Behavior of PE-b-PEO Diblock Copolymers

Abstract

In this study, spherical, lamellar, and aligned lamellar types of polyethylene-b-poly(ethylene oxide) (PE-b-PEO) diblock copolymers were prepared and comparatively foamed with CO2 to understand the influence of microphase morphology and long-range ordering on foaming behavior. The experimentally measured melting point, CO2 solubility, and interfacial tension in the presence of CO2 indicated the potential of CO2-philic PEO block acting as bubble nuclei. Scanning electron microscopy results revealed that lamellar PE-b-PEO produced open cells all the way, whereas spherical PE-b-PEO created closed cells at low temperature and mesh-like openings at high temperature. Continuous PEO microdomains directly provide numerous potential opening channels and therefore induce the bursting of cells. The drastic biaxial stretching of cell walls at high temperature turns the embedded discrete PEO spheres into those channels responsible for the distinct mesh-like perforations. As for the flow aligned lamellar PE-b-PEO, submicron open cells were fabricated with a regular multilayered pattern. Long-range ordering not only suppresses the undesired coalescences but also preserves the self-assembled pattern. Foaming mechanisms, mainly focused on the bubble growth, were finally uncovered for different morphological PE-b-PEO block copolymers, complete understanding of which will be of importance in the block copolymer design to meet the requirement on foam structures.