General-Purpose Coarse-Grained Toughened Thermoset Model for 44DDS/DGEBA/PES.

The objective of this work is to predict the morphology and material properties of crosslinking polymers used in aerospace applications. We extend the open-source dybond plugin for HOOMD-Blue to implement a new coarse-grained model of reacting epoxy thermosets and use the 44DDS/DGEBA/PES system as a case study for calibration and validation. We parameterize the coarse-grained model from atomistic solubility data, calibrate reaction dynamics against experiments, and check for size-dependent artifacts. We validate model predictions by comparing glass transition temperatures measurements at arbitrary degree of cure, gel-points, and morphology predictions against experiments. We demonstrate for the first time in molecular simulations the cure-path dependence of toughened thermoset morphologies.

Sequential thiol click reactions: formation of ternary thiourethane/thiol-ene networks with enhanced thermal and mechanical properties.

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.

Impact properties of thiol-ene networks.

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.

Characterization of mouthguard materials: thermal properties of commercialized products.

OBJECTIVES: Several mechanisms have been purported to describe how mouthguards protect the orofacial complex against injury. As the properties needed for these mechanisms to be effective are temperature and frequency dependent, the specific aim of this study was to provide a comprehensive thermal characterization of commercial mouthguard materials. METHODS: Five commercially representative thermoplastic mouthguard materials (Essix Resin, Erkoflex, Proform-regular, Proform-laminate, and Polyshok) were tested. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were implemented to measure thermal transitions and mechanical properties. Measurements were conducted three times per sample. One-way ANOVA and one-sample t-tests were used to test for differences between commercial products on selected mean thermal property values. RESULTS: The DSC measurements indicated no differences between commercial materials for mean glass transition (p=0.053), onset melt (p=0.973), or peak melt (p=0.436) temperatures. Likewise, DMA measurements revealed no differences between commercial materials for the mean glass transition (p=0.093), storage modulus (p=0.257), or loss modulus (p=0.172) properties, respectively. The one-sample t-tests revealed that glass transition temperatures were different from intra-oral temperature (p<0.005) for all materials. SIGNIFICANCE: Commercialized mouthguard materials are sensitive to repetitive heating and cooling cycles, prolonged thermal treatment, and have glass transitions well below their end-use intra-oral temperature. As such, these materials are functioning as elastomers and not optimal mechanical damping materials. Dental clinicians, healthcare practitioners, or end-users should be aware that these materials are at best problematic with respect to this protective mechanism.