The comprehensive approach towards study of (azo)polymers fragility parameter: Effect of architecture, intra- and intermolecular interactions and backbone conformation

The comprehensive investigations including the influence of architecture, intra- and intermolecular interactions and backbone conformation on the glass transition activation energy and the temperature dependence of segmental relaxation (fragility) in a series (azo)polyimides are presented. The studies were carried out using DSC measurements. To understand the microscopic parameters that control the glass transition phenomenon the activation energy was calculated using two different approaches, i.e., Kissinger and Moynihan models. The behavior of polyimides near the glass transition was investigated in the context of formation intra- and intermolecular H-bonds, which impact on rigidity and conformation of main and side chains of the polymers. Presence of the H-bonds was confirmed experimentally by H-1 NMR and FTIR spectroscopes and theoretically by DFT simulations. Our investigations showed, that the presence of intra- and intermolecular interactions cause different conformations of the polymer chain, what may be the key to solve the puzzle of fragility parameter of polymers.