Thermal insulative 2D-oriented bimodal micro-foams and high strength photonic thermoplastic elastomers by assembling olefin multiblock copolymers

Abstract

Hierarchical 2D-oriented micro-foams and photonic elastomers are produced by assembling the mesophase separated and crystallized superstructures of olefin multiblock copolymers (OBCs). Highly 2D-oriented monomodal and bimodal micro-foams are prepared via compression molding of as-received nascent OBC pellets, irradiation crosslinking, and a subsequent moderate-to-high-pressure supercritical CO2 foaming. Randomly short range ordered bimodal micro-foams are generated from the sheared counterparts. These micro-foams show excellent lightweight properties with foam density of 0.061–0.188 g cm−3 and outstanding thermal conductivity of 20–36 mW m−1 K−1 by laser flash analysis. Moreover, the order-disorder and order-order transitions of nascent and sheared bulk OBCs are characterized by a sequential annealing and subsequent crystallization procedure. The self-seeded nascent and sheared OBCs show hierarchical mesophase separation with domain spacings of 80–258 nm, measured by ultra-small X-ray scattering. The selective visible-light transmitted, transparent, and high-strength thermoplastic elastomers are then made via solvent-free compression molding of these OBC pellets. Meanwhile, low-temperature Sc-CO2 foaming shows that 2D lamellar crystals and 2D, 3D-growing spherulitic crystals with sharp interfaces are individually organized within 2D-oriented lamellar domains of photonic and opaque sheets, which account for their high tensile strength and low strain hardening properties, respectively. The 2D-oriented bimodal micro-foams and assembled photonic elastomers possess potential applications in lightweight sound and thermal insulation, auto-parts, shape memory light actuators, and soft sensors.