Throughout the past decade, investigations of thick thermoset thiol–ene networks (TENs) have become increasingly prominent in the literature due to facile, quantitative synthesis giving rise to unique network characteristics, specifically high mechanical energy damping. This article reports the synthesis and thermomechanical properties of ternary thiol–thiol–ene systems that exhibit tunable glass transitions that maintain high, narrow tan δ values in the glass transition region. We begin with a base network of a trifunctional thiol and a trifunctional ene and then systematically substitute the trifunctional thiol with a series of difunctional thiols while maintaining stoichiometric balance between total thiol and ene content. The resultant ternary networks exhibit glass transition temperatures that follow the Fox equation. In contrast to other ternary thiol–ene networks, we observe minimal broadening of the glass transition region, which implies that we can retain the energy-absorbing capabilities of the thiol–ene system. This approach has high potential as a simple tool for scientists and researchers to tune T gs for select networks without detrimentally affecting other physical properties.

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In this study, a series of thiol-ene networks having glass transition temperatures ranging from -30 to 60 °C were synthesized utilizing several multifunctional thiols and two trifunctional alkenes. Thermomechanical properties were determined using dynamic mechanical analysis, and impact properties were determined using pendulum impact and drop impact testing protocols. The impact behavior was found to directly correlate to the glass transition temperature, except when the temperature at which the impact event occurs overlaps with the range of temperatures corresponding to the viscoelastic dissipation regime of the polymer. Additionally, we discuss insight into the spatial limitations of energy dissipation for thiol-ene network polymers and establish a platform for predictability in similar systems.

We report the physical properties of thiol-ene networks modified with thiourethane or urethane linkages, either along the main chain or as a branched component in the network, respectively. Because of the robust and orthogonal nature of thiol-isocyanate and thiol-ene reactions, these networks can be formed in a two-step, one-pot synthesis. Resultant networks were characterized using dynamic mechanical analysis, mechanical testing and other complementary techniques. It was found that incorporating (thio)urethanes into the networks increased Tg, but also increased strain at break and toughness while decreasing cross-link density. The changes in physical properties are discussed in terms of a proposed dual network morphology. These facile modifications to thiol-ene networks demonstrate how molecular-level, nanoscale changes can have a profound influence on the macroscale properties through hierarchical development of network morphology.

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