Molecular network development of a thermosetting epoxy-amine polymer
Epoxy-amine resins find wide application as the matrix material of high performance polymer composites due to their favorable mechanical properties, thermal properties and solvent stability. These properties are derived from the complicated, highly crosslinked molecular network that is characteristic of these thermoset polymers. The connectivity of the molecular network has a strong influence on the physical performance of the finished part. Non-homogeneity in the network structure can degrade these favorable properties through the introduction of low-energy pathways for solvent penetration or fracture propagation. This work examines nanoscale variation in the crosslink density of the epoxy-amine network. Specific attention is paid to the influence of cure temperature on the network-building reaction and the subsequent effect on the architecture of the crosslinked molecular network. Thermal, rheological and spectroscopic techniques are used to monitor key chemical and structural changes during network growth. Atomic force microscopy is used to understand nanoscale fracture behavior in terms of the low energy pathways that result from a non-homogeneous distribution of crosslink density. The influence of processing-induced changes in molecular connectivity is discussed in terms of observed nanoscale morphology and fracture properties of the cured material.