Real‐time in situ monitoring of the thermal cure of a bisphenol cyanate: A view toward intelligent processing

Applications

“…It would be easy to think that the >C¼ ¼C< bond band could be monitored quantitatively directly and this can indeed be the case [152,153]. Vinyl and acrylate monomers have been largely described here but other systems have also been reported such as cyanate esters [158], epoxies [159], melamine-formaldehydes [160], polyimides [161] and polyurethanes [162]. This is usually carried out by choosing a band not affected by the reaction being followed.…”

Cyanate Esters

“…In-line fiber optical Raman spectroscopy was shown to be an effective real-time monitoring tool, for example, when a bisphenol E dicyanate ester resin was prepared from Arocy L-10 [42]. In a univariate approach, the authors monitored the reaction progress by using indicative changes at specific bands in the Raman spectrum: the shifting of a peak at 801 cm 21 into a new mode at 854 cm 21 with a low-and a high-energy shoulder (due to branching at the alpha carbon as the first step in the cyclization reaction) and the splitting of the ether linkage mode at 1193 cm 21 into two modes at 1172 and 1203 cm 21 .…”

Processing

“…Both methods are applicable under process conditions, and robust equipment (spectrometers, sensors) that can be used in an industrial environment is readily available. Raman spectroscopy has been used for the real-time in situ monitoring of the thermal cure of a bisphenol cyanate [14]. The synthesis as well as the curing of phenol formaldehyde resol has been studied by Raman spectroscopy [15].…”

“…Of course, by using chemometrics, the significance of Raman and FTIR can be much enhanced, since multivariate data analysis poses several advantages over univariate data analysis. For instance, already nearly 20 years ago, Cooper et al [14] in their Raman study on the curing of cyanate ester resins compared univariate (basically, single peak-based) with multivariate (full spectrum-based) data analysis, and found multivariate data analysis superior in that it eliminated spectral interferences and included all spectral information in the regression analysis instead of only singular peaks, which, in turn, improved the accuracy of their predictions. With multivariate data analysis, no internal reference peaks were required.…”

“…Especially with baking enamels based on polycondensation resins, such "overcuring" represents a big problem. However, lower cross-linking densities may also be advantageous: in the case of cyanate esters, it is known that when the curing reaction is stopped at a conversion of around 85%, increased density, dielectric constant, Young's modulus, and solvent absorption properties are obtained compared to the completely cured cyanate ester resin [14,43]. On the other hand, completely cured cyanate ester resin will exhibit improved hydrolytic stability and higher glass transition temperature [14].…”