Epoxy-amine resins find wide application as the matrix material of high performance polymer composites because of their favorable mechanical properties, thermal properties and solvent stability. These properties result from the complicated, highly cross-linked molecular network that is characteristic of epoxy-amine thermoset polymers. The connectivity of the molecular network has a strong influence on the physical performance of the finished part. Nonhomogeneity 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 the influence of cure temperature on the network-building cross-linking reaction and the subsequent effect on the homogeneity of the cross-linked molecular network. Specific attention is paid to nanoscale variation in the distribution of cross-link density. 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 nonhomogeneous distribution of cross-link 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.

A renewable bisphenol, 4,4'-(butane-1,4-diyl)bis(2-methoxyphenol), was synthesized on a preparative scale by a solvent-free, Ru-catalyzed olefin metathesis coupling reaction of eugenol followed by hydrogenation. After purification, the bisphenol was converted to a new bis(cyanate) ester by standard techniques. The bisphenol and cyanate ester were characterized rigorously by NMR spectroscopy and single-crystal X-ray diffraction studies. After complete cure, the cyanate ester exhibited thermal stability in excess of 350 °C and a glass transition temperature (Tg ) of 186 °C. As a result of the four-carbon chain between the aromatic rings, the thermoset displayed a water uptake of only 1.8% after a four day immersion in 85 °C water. The wet Tg of the material (167 °C) was only 19 °C lower than the dry Tg , and the material showed no significant degradation as a result of the water treatment. These results suggest that this resin is well suited for maritime environments and provide further evidence that full-performance resins can be generated from sustainable feedstocks.

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A new polycyanurate network exhibiting extremely low moisture uptake has been produced via the treatment of perfluorocyclobutane-containing Bisphenol T with cyanogen bromide and subsequent thermal cyclotrimerization. The water uptake, at 0.56 ± 0.10% after immersion in water at 85 °C for 96 h, represents some of the most promising moisture resistance observed to date in polycyanurate networks. This excellent performance derives from a near optimal value of the glass transition at 190 °C at full cure. Superior dielectric loss characteristics compared to commercial polycyanurate networks based on Bisphenol E were also observed. Polycyanurate networks derived from this new monomer appear particularly well-suited for applications such as radomes and spacecrafts where polycyanurates are already widely recognized as providing outstanding properties.