The mechanism of the curing reactions of cyanate polymer resins based on Bisphenol A dicyanate has been investigated both in solution and in the solid state by NMR spectroscopic techniques. To increase S/N and to unambiguously characterize the reactions of the cyanate functionalities, 13C-and 16N-enriched cyanate resins and monocyanate model compounds were used, the latter yielding soluble and isolable analogs.In solution, the main reaction is formation of triazine rings as identified by NMR and MS techniques and characterized by single-crystal X-ray diffraction on an isolated crystalline compound from the monocyanate model compound. Side products are formed by the reaction of the cyanate functionalities with trace water present in the solvent but there is no NMR evidence for the formation of dimeric or other intermediate species prior to triazine ring formation. The isolated resins from the solution curing and also those formed directly by heat curing of the neat resin were characterized by high-resolution solid-state NMR. In the former case triazine ring formation and the presence of side products were confirmed by both 13C and 16N solid-state NMR and their proportions quantified. In the case of the neat resin, the curing reaction is shown to be almost quantitative. This is rationalized in terms of the very strong intermolecular intercyanate bonding interactions observed in the crystal structure of the Bisphenol A dicyanate monomer obtained from a single-crystal X-ray diffraction experiment.

Orr, G. L; Hess, F. D. Mechanism of action of the diphenyl ether herbicide acifluorfen-methyl in excised cucumber (Cucumis sativus) cotyledons. Plant Physiol. 1982, 69, 502-507. Ridley, S. M. Interaction of chloroplasts with inhibitors. Effects of two diphenyl ether herbicides, fomesafen and nitrofluorfen, on electron transport and some comparisons with dibromothymoquinone, diuron and paraquat. Plant Physiol. 1983, 72, 461-468.

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The uptake of water by nylon 6,6 [42DB Adipure (trade name of Dupont Canada Inc.)] at 100°C has been monitored by a combination of one‐dimensional proton NMR spectroscopy, relaxation time (T1 and T2) measurements and proton microscopic NMR imaging techniques. The relaxation times of the water absorbed into the nylon matrix are very short at room temperature, (T2 < 1 ms and T1 ≈ 1 s) indicating that the water is located in a highly restricted environment and suggesting that strong interactions exist between the absorbed water and the polymer. The diffusion profiles measured at room temperature indicate that the diffusion of water into nylon 6,6 at 100°C is Case I Fickian diffusion. The spatial dependence of the T2 relaxation time constant and its variation with the water content was also examined. The results reveal that both T2 and T2* decrease toward the center of the sample in samples that have a concentration gradient of sorbed water. In fully saturated samples, no spatial dependence was observed. The overall values of T2 and T2* are also observed to increase as a function of exposure time. An evaluation of the desorption process at room temperature and at 100°C was performed. A continuous, exponentially decreasing solvent profile was observed for the desorption process which again indicates Case I Fickian kinetics. The exchange process of external bulk and atmospheric water with deuterium oxide (D2O) saturated nylon rods has also been studied using the microscopic imaging technique. © 1993 John Wiley & Sons, Inc.

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