Dielectric Study of the Effect of a Sol‐Gel Inorganic Network on Polymeric Relaxation Dynamics in Acrylic/Titania Hybrids

Summary: In this research, poly[(methyl methacrylate)‐co‐(butyl methacrylate)‐co‐(methacrylic acid)]/TiO2 hybrids were prepared by the sol‐gel process. The copolymer composition was 16 mol‐% methyl methacrylate (MMA), 80 mol‐% butyl methacrylate (BMA) and 4 mol‐% methacrylic acid (MA). The dielectric properties of the hybrids with varying titania content were measured over the frequency range 0.1 Hz to 100 kHz and between 25 and 160 °C. In addition, the hybrids were investigated using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). In the given frequency range, a single relaxation peak was observed both by dielectric relaxation spectroscopy (DRS) and DMTA. The single relaxation observed by DRS behaves in the manner of an α‐relaxation, with the frequency–temperature locus showing non‐Arrhenius behavior (curved downwards like a VTF law). The change in the DRS and DMTA characteristics in hybrids compared to the pure polymer reflect the presence of antagonistic mechanisms controlling the dynamics of the polymer chains: nanodomains with enhanced and restricted mobilities are suggested to be responsible for the broadening of the isochronal dielectric loss curve toward, respectively, the low and the high temperature sides. Combining the DSC and DRS results, it can be inferred that the domains with enhanced mobility result from internal and external plasticization effects that reduce the intermolecular hydrogen bonds between the polymer chains. Besides, the motion of polymer chains is found to be significantly hindered by the titania network, due to the presence of iono‐covalent bonds between the polymer and titania and geometrical restrictions in high junction‐point density and titania‐rich microphases. From the Arrhenius plot, it is also shown that the addition of sol‐gel titania more severely hinders the segmental motion of the macromolecular chains than the local motion of the lateral groups (β relaxation). Simplified schematic morphology for the poly(MMA‐co‐BMA‐co‐MA)/TiO2 hybrids. magnified image Simplified schematic morphology for the poly(MMA‐co‐BMA‐co‐MA)/TiO2 hybrids.