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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.

We report on the control of cyclotrimerization forming a polycyanurate polymer using magnetic iron oxide nanoparticles in an alternating-current (ac) field as an internal heat source, starting from a commercially available monomer. Magnetic nanoparticles were dispersed in the monomer and catalytic system using sonication, and the mixture was subjected to an alternating magnetic field, causing the magnetic nanoparticles to dissipate the energy of the magnetic field in the form of heat. Internal heating of the particle/monomer/catalyst system was sufficient to start and sustain the polymerization reaction, producing a cyanate ester network with conversion that compared favorably to polymerization through heating in a conventional laboratory oven. The two heating methods gave similar differential scanning calorimetry temperature profiles, conversion rates, and glass transition temperatures when using the same temperature profile. The ability of magnetic nanoparticles in an ac field to drive the curing reaction should allow for other reactions forming high-temperature thermosetting polymers and for innovative ways to process such polymers.

The co-cyclotrimerization of two tricyanate ester monomers, Primaset PT-30 and 1,2,3-tris(4-cyanato)propane (FlexCy) in equal parts by weight with Primaset LECy, a liquid dicyanate ester, was investigated for the purpose of exploring synergistic performance benefits. The monomer mixtures formed stable, homogeneous blends that remained in the supercooled liquid state for long periods at room temperature, thereby providing many of the processing advantages of LECy in combination with significantly higher glass transition temperatures (315-360 °C at full cure) due to the presence of the tricyanate-derived segments in the conetwork. Interestingly, the glass transition temperatures of the conetworks after cure at 210 °C, at full cure, and after immersion in 85 °C water for 96 h were all higher than predicted by the Flory-Fox equation, most significantly for the samples immersed in hot water. Conetworks comprising equal parts by weight of PT-30 and LECy retained a "wet" glass transition temperature near 270 °C. The onset of thermochemical degradation for conetworks was dominated by that of the thermally less stable component, while char yields after the initial degradation step were close to values predicted by a linear rule of mixtures. Values for moisture uptake and density in the conetworks also showed behavior that was not clearly different from a linear rule of mixtures. An analysis of the flexural properties of catalyzed versions of these conetworks revealed that, when cured under the same conditions, conetworks containing 50 wt % PT-30 and 50 wt % LECy exhibited higher modulus than networks containing only LECy while conetworks containing 50 wt % FlexCy and 50 wt % LECy exhibited a lower modulus but significantly higher flexural strength and strain to failure. Thus, in the case of "FlexCy", LECy was copolymerized with a tricyanate that provided both improved toughness and a higher glass transition temperature.

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.