Effect of matrix−nanoparticle supramolecular interactions on the morphology and mechanical properties of polymer foams

• Published in: Polymer international 2018-07, Vol.67 (7), p.859-867
• Main Authors: Jamalpour, Seifollah, Ghaffarian, Seyed Reza, Jangizehi, Amir
• Format: Article
• Language: English
• Subjects: Cell density; Cellular structure; Cytology; Dimers; DMTA; Fillers; Foaming; Hydrogen bonding; Mechanical properties; microcellular foaming; Modulus of elasticity; Molecular structure; Morphology; Nanocomposites; Nanoparticles; nanosilica; Organic chemistry; Plastic foam; Polyhydroxyethyl methacrylate; Polymers; Silica; Silicon dioxide; supramolecular polymer nanocomposites; Thermomechanical properties; ureido‐pyrimidinone; Viscoelasticity
• ISSN: 0959-8103; 1097-0126
• DOI: 10.1002/pi.5536

In this study, we report the fabrication of supramolecular polymer nanocomposite foams with a uniform cell structure, high cell density and high expansion ratio using a soft matrix of poly(methyl acrylate‐co‐2‐hydroxyethyl methacrylate) and silica nanoparticle fillers, both functionalized with ureido‐pyrimidinone (UPy) supramolecular groups. Microcellular structures were formed using a batch foaming process at 90 °C under a 9 MPa nitrogen atmosphere. Nanocomposites were characterized and compared before and after the foaming process to investigate the effect of supramolecular interactions on the thermomechanical properties and morphology of the foams. TEM images revealed that while strong inter‐filler supramolecular interactions do not have a positive effect on their dispersion state, matrix−filler interactions derived from hydrogen bonding UPy motifs result in a rather uniform distribution of nanoparticles. Competing filler−filler and matrix−filler supramolecular interactions can be balanced and optimized by adjusting UPy populations along the chains and on the surface of nanoparticles. At a given chain functionality, increasing the nanoparticle loading up to an optimum concentration improves the mechanical properties and formability of the system. Above such concentration strong interactions between fillers, which are not compensated by the matrix, result in large aggregates and consequently undermine the material performance. Supramolecular polymer foams illustrate a similar thermal and viscoelastic behavior to that of neat samples but after foaming, due to the formation of a cellular structure and rearrangement or dissociation of UPy dimers under the foaming conditions, the elastic modulus is reduced. © 2018 Society of Chemical Industry Poly(MA‐co‐HEMA) as a polymer with low strength together with ureido‐pyrimidinone (UPy) functionalized silica nanoparticles were used for the fabrication of supramolecular polymer nanocomposite foams with uniform cell structure, high cell density and a high expansion ratio via batch foaming at 90 °C, 9 MPa, for 5 h using N2 as a physical blowing agent.