Smart semi-interpenetrated polymer networks from functional silicones and UV-cured polymethacrylic acid: The role of ionic interactions

In this work, semi-interpenetrated polymer networks (semiIPNs) were developed coupling a supramolecular noncovalent network with a UV-cured one in a poly(dimethylsiloxane) (PDMS)-based elastomer. Ionic driven supramolecular assembly was achieved via acid-base proton transfer reaction by blending amine groups, belonging to the side chains of the PDMS-based polymer, and acidic groups, coming from methacrylic acid. Additionally, the C--C double bonds were UV-cured, leading to the formation of the final semiIPNs. Multiple formulations were developed by varying the ionic bond density, namely the amine protonation degree, to study the correlation between the polymer structure and the rheological and self-healing properties. Flow curve analyses confirmed the formation of efficient ionic assemblies upon blending, showing an increase of the Newtonian viscosity of the blends at 25 C as the ionic bond density increased. Moreover, Fourier-transform infrared spectroscopy evidenced the appearance of the peaks associated to the ammonium carboxylate ions, supporting the achievement of the supramolecular network. Particular attention was given to the study of the effect of environmental moisture on the semiIPNs properties, which was found to highly influence the rheological, the mechanical and the self-healing properties.