Kinetics of the epoxy–thiol click reaction initiated by a tertiary amine: Calorimetric study using monofunctional components

• Published in: Thermochimica acta 2015-09, Vol.616, p.79-86
• Main Authors: Loureiro, Roi Meizoso, Amarelo, Tánia Carballeira, Abuin, Senen Paz, Soulé, Ezequiel R., Williams, Roberto J.J.
• Format: Article
• Language: English
• Subjects: Click chemistry; DSC; Epoxy–thiol reaction; Induction period; Kinetics; Tertiary amine
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2015.08.012

•Reaction kinetics of a monoepoxy and a monothiol was studied by DSC.•Benzyldimethylamine (BDMA) was used as initiator.•Reaction exhibited a long induction period followed by a fast autocatalytic rate.•A mechanistic kinetic model provided a reasonable fitting of the kinetic behavior.•The formulation simulates the behavior of room-temperature-cure commercial epoxies. An analysis of the kinetics of the epoxy–thiol reaction in a model stoichiometric system of monofunctional reagents, 3-mercaptopropionate (BMP) and phenylglycidylether (PGE) is reported. Benzyldimethylamine (BDMA) was employed as initiator in amounts ranging from 0.5 to 2wt%. These formulations showed a kinetic behavior qualitatively similar to that of commercial adhesives and coatings formulated for a room-temperature cure. Isothermal DSC scans revealed the existence of a relatively long induction period preceding a fast autocatalytic reaction step. Dynamic DSC scans showed that the reaction was shifted to a lower temperature range by increasing the storage period of the initial formulation at 20°C. This unusual kinetic behavior could be modeled assuming that thiolate anions, slowly generated during the induction period, initiated a fast autocatalytic propagation/proton transfer reaction. The kinetic model included a pseudo-steady state for the initiator concentration and an equilibrium reaction between epoxy and OH groups generated by reaction. A reasonable fitting of isothermal and dynamic DSC runs was achieved in a broad range of temperatures and amine concentrations. In particular, both the length of the induction time and the effect of the storage period were correctly predicted.