Analysis of the reaction mechanism of the thiol–epoxy addition initiated by nucleophilic tertiary amines

Abstract

The mechanism of thiol–epoxy reactions has been analyzed from a theoretical point of view and modelled using experimental kinetic data.

Sequential heat release: an innovative approach for the control of curing profiles during composite processing based on dual‐curing systems

“…At temperatures as low as 30 °C, in the first process one can appreciate an induction period of about 90 min that indicates that there should be enough time to inject the sample in the mould cavity before the reaction starts. It is also observed that the first process has a very strong autocatalytic behaviour, as reported previously, and therefore there is a serious risk of temperature runaway if the programmed temperature is too high. Given that crosslinking would take place entirely in the second curing stage and that the first curing process is much faster and more exothermic than the second one, the key point to ensure uniform crosslinking during processing of the composite part will be to control the exothermicity during the first curing process, so that the second curing process does not start.…”

“…Both reactions are depicted in Scheme (right‐hand side). The reaction mechanisms of nucleophile‐initiated thiol–epoxy polymerization and epoxy homopolymerization have been recently discussed in detail elsewhere . Because the kinetics of the second process are much slower than the first one, it has been possible to develop recently a new family of dual‐curable thermosetting materials that have found, so far, an application in shape‐memory devices …”

“…The curing of the simple formulation DGS3‐1 starts shortly after the composite reaches 70 °C and, due to the autocatalytic characteristics of the reaction and the high reaction rate, a large temperature overshoot occurs in the centre of the composite part leading to very fast completion of the reaction, and diverging conversion across the thickness of the part, meaning that the crosslinking process ( x epoxy, gel = 0.80) is far from being uniform. In the case of formulation DGS3‐0.5, there is an earlier temperature overshoot because the reaction can start earlier, leading to fast conversion rate in the centre of the part and completion of the first reaction process (occurring at x epoxy = 0.5). However, given that the second reaction is much slower, the final conversion after the temperature overshoot does not exceed x epoxy = 0.55, which is only slightly higher than the conversion in the part surface, and still lower than the conversion at the gel point x epoxy, gel = 0.63.…”

“…For this expression to be valid, there should be a controlled curing sequence and therefore good separation between processes, as is commonly observed in off‐stoichiometric thiol–epoxy systems …”

High-Tg, Low-Dielectric Epoxy Thermosets Derived from Methacrylate-Containing Polyimides

“…Epoxy resins are commonly cured by active hydrogen-containing compounds such as phenol novolac, bisphenol A novolac, dicyandiamide, and diamine [4][5][6][7][8][9][10][11][12][13]. However, the reaction product from active hydrogen and epoxy lead to a secondary alcohol.…”