Improving microcellular foamability of amorphous supramolecular polymers via functionalized nanosilica particles

This work introduces and investigates a synergistic approach to tailor microcellular morphology and physical properties of soft polymer foams by simultaneously utilizing supramolecular associations and nanoparticle inclusions. For this purpose, supramolecular nanocomposite foams consisting of soft amorphous polyacrylates and silica nanoparticles are successfully prepared and characterized. The polymer precursors as well as the nanoparticles are all functionalized with ureido‐pyrimidinone (UPy) supramolecular groups at various contents. Microcellular foams are produced in a batch process at 90°C after a 5‐h saturation step in 9 MPa, using supercritical N₂ as the physical foaming agent. The effects of UPy‐grafting on microcellular morphology and consequently on thermal, viscoelastic, and mechanical properties is investigated. Dispersion of nanoparticles as well as the cellular structure of supramolecular nanocomposite foams is analyzed in relation to supramolecular moiety‐grafting density. It is illustrated that strong quadrupole hydrogen bonding between the filler and matrix not only improves the degree of reinforcement in nanocomposites, but also stabilizes bubble growth and retards cell coalescence or rupture. An optimum average cell size and microcellular density, that is, 6 ± 0.2 μm and 6 × 10⁹ cells/cm³, respectively, is achieved with only 4 wt% UPy‐functionalized nanoparticle loading. These results illustrate, therefore, that supramolecular interactions between the chain backbone and nanoscale inclusions can open new horizons to architect and exploit microcellular materials consist up of amorphous, soft, loosely entangled polymers. POLYM. COMPOS., 40:364–378, 2019. © 2017 Society of Plastics Engineers