2022 Volume 48 Issue 6 Pages 217-222
The structure of phenolic resins depends on the pH under which the resin intermediate is produced. Resins intermediates produced under acidic conditions are called novolacs, and those obtained under alkaline conditions―resols. In this study, the activation energy and heat of the reaction that produces novolac and resol, followed by a thermosetting reaction, were obtained using quantum chemical calculations and used in molecular dynamics simulations of the reaction. The calculated resin structures were evaluated for each degree of curing, and the results showed that the structures were generally reasonable. The glass transition temperature increased with the degree of curing and tended to be higher for resol resins than for novolac resins. This trend is qualitatively consistent with the experimental data. The higher glass transition temperatures of resol resins may reflect the two-dimensional spreading of bonds owing to ortho- and para-orientation of chemical bonds during the formation of resins from resols. The reason for the higher glass transition temperatures of novolac resins at 20% conversion was analyzed, and it was attributed to the intermolecular forces being greater than in resol resins.
