Thermomechanical Characterization of High Tg Disulfide-Containing Thermoplastic Polyimides
Authors: Margaret A. Hall, Broderick Lewis, Kenneth R. Shull
Journal: Macromolecules
Abstract: Covalent adaptable networks are frequently studied as alternatives to conventional thermosetting polymers because they can be recycled and reprocessed; however, the inclusion of dynamic covalent bonds within high-temperature (or high-performance) engineering thermoplastics remains largely unexplored. In this work, dynamic disulfide-containing thermoplastic polyimides were synthesized and compared to nondynamic thermoplastic polyimides. The thermomechanical properties of these polymers were examined by utilizing several techniques, including thermogravimetric analysis, differential scanning calorimetry, along with the use of the rheometric quartz crystal microbalance, and traditional dynamic mechanical analysis. The resulting experimental data suggest that the thermal stability of the dynamic compositions was slightly reduced in comparison to the nondynamic analogs, but the dynamic compositions exhibit a similar mechanical response under service conditions. The dynamic compositions also demonstrated significantly easier reprocessability via compression molding than their nondynamic counterparts.
Drying oils such as linseed oil form a polymer network through a complex free-radical polymerization process. We have studied polymerization in this challenging class of polymers using a quartz crystal microbalance (QCM). The QCM is able to measure the evolution of polymer mass and mechanical properties as the oil transitions from a liquid-like to a solid-like state. Measurements using bulk materials and thin films provide information about the initial polymerization phase as well as the evolution of the mass and mechanical properties over the first two years of cure. The temperature-dependent response of the cured linseed oil films was also measured. These results were combined with previously published results obtained from traditional dynamic mechanical analysis to give a unified picture of the properties of these materials across a very broad temperature range.
