Molecular dynamics in nanostructured polyimide‐silica hybrid materials and their thermal stability

Abstract

AbstractMolecular motion and thermal stability in two series of nanophase‐separated polyimide‐silica (PI‐SiO2) hybrid networks with chemically bound components were studied. The hybrids were prepared via a sol‐gel process and differed in PI structure and chain length, and in SiO2 content ranging from 10 to 50 wt.%. Differential scanning calorimetry, laser‐interferometric creep rate spectroscopy, dielectric relaxation spectroscopy, thermally stimulated depolarization current techniques, and thermogravimetry were used covering, on the whole, the ranges of 100–900 K and 10−3‐109 Hz. Silica domains influenced PI dynamics in two opposite directions. Loosened segmental packing in chains confined to nanovolumes resulted mainly in rise of small‐scale motion below β‐relaxation region, while anchoring of chain ends to ‘rigid walls’ caused, contrarily, a partial or total suppression of segmental motion above Tβ, especially drastically at the temperatures close to and within glass transition. The latter resulted in a large change in thermal stability, e.g., 2.5‐fold increasing of the apparent activation energy of thermooxidative degradation, and more than 100° rise of predicted long‐term thermal stability for the hybrids as compared to that for PI.