Optimization of Self Healing Polyether–Polythioether Networks via Factorial Design in Epoxy/Thiol–Ene Photopolymerizations
Ricardo Acosta Ortiz *
Centro de Investigacion en Quimica Aplicada, Blvd Enrique Reyna #140, Saltillo- 25294, Mexico.
Roberto Yañez Macias
Centro de Investigacion en Quimica Aplicada, Blvd Enrique Reyna #140, Saltillo- 25294, Mexico.
*Author to whom correspondence should be addressed.
Abstract
Aim: The study aims to optimize the self-healing behaviour of polyether–polythioether co-networks containing dynamic disulfide bonds produced via epoxy/thiol–ene photopolymerisation.
Study Design: A factorial design of experiments (DoE) evaluating the effects of thiol–ene system (TES) concentration, tributylphosphine (TBP) concentration, and healing temperature.
Methodology: Self-healing functionality was introduced by synthesizing a disulfide–thiol oligomer, which was subsequently incorporated into a photocurable formulation that included a bio-based epoxy resin, a tetraallyl ditertiary amine curing agent, and a photoinitiator. After photopolymerization, the resulting specimens were cut into two halves and subjected to thermal treatment to promote rejoining. A factorial DoE was performed by varying TES concentration, TBP concentration, and temperature. Healing time, defined as the time required for the two halves of the specimen to fully rejoin chemically, was recorded for each experimental condition. Statistical analysis was carried out using ANOVA.
Results: Healing efficiency exhibited a strong dependence on experimental factors. Higher temperatures and increased TBP concentrations consistently led to shorter healing times, with the fastest healing (5 min) achieved at 80 °C under elevated TBP levels. ANOVA confirmed that the model accurately described the experimental data, with a highly significant overall p-value (0.015), indicating that the selected factors collectively accounted for most of the variability in healing time. The linear component of the model contributed the largest share of variance (SS = 2067.38), and its associated p-value (0.01) demonstrated that the primary effects of the factors were statistically significant.
Conclusion: Optimal healing conditions were identified as 40 mol% TES, 1 mol% TBP, and a temperature of 80 °C, under which complete healing was achieved in only 5 minutes.
Keywords: Epoxy resin, thiol–ene photopolymerisation, self-healing polymers, polyether–polythioether co-networks, disulfide bonds, thiol–disulfide exchange, tributylphosphine, dynamic covalent networks