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A concise series of renewable vinyl compounds has been prepared from benign biosourced precursors, vanillin and eugenol, in fair overall yield. These were evaluated against styrene as reactive diluents in a renewable high-performance vinyl ester resin thermoset: dimethacrylated-epoxidized-sucrose-soyate (DMESS). Each diluent contained a 1,2-dimethoxybenzene or veratrole core structure that connotes a decreased vapor pressure and thereby reduced exposure hazard. Viscosities for formulations (10, 20, and 30% by weight of diluents) with styrene and all three veratrole-diluents were evaluated. Veratrole-diluents were comparable to styrene at similar molar concentration. Thermosets formulated with 30% by weight of diluents were prepared and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA); the most promising thermoset was prepared using 3-allyl-1,2-dimethoxy-5-vinylbenzene-diluted-DMESS and closely matched the performance of the styrene-diluted thermoset in terms of thermal stability, glass transition temperature, toughness, and tensile strength.

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Abstract:With the increase in structural applications of bio-based composites, the study of long-term creep behavior of these materials turns into a significant issue. Because of their bond type and structure, natural fibers and thermoset resins exhibit nonlinear viscoelastic behavior. Time-temperature superposition (TTS) provides a useful tool to overcome the challenge of the long time required to perform the tests. The TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior, therefore creep tests performed at elevated temperatures may be converted to tests performed at longer times. In this study, flax fiber composites were processed with a novel liquid molding methacrylated epoxidized sucrose soyate (MESS) resin. Frequency scans of flax/MESS composites were obtained at different temperatures and storage modulus and loss modulus were recorded and the application of horizontal and vertical shift factors to these viscoelastic functions were studied. In addition, short-term strain creep at different temperatures was measured and curves were shifted with solely horizontal, and with both horizontal and vertical shift factors. The resulting master curves were compared with a 24-h creep test and two extrapolated creep models. The findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curves for loss modulus and storage modulus, while use of only horizontal shift factors for creep data provides acceptable creep strain master curves. Based on the findings of this study, flax/MESS composites can be considered as thermorheologically complex materials.

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We have developed a convenient protocol for functionalization of b-pyranones. Conjugate radical addition and tandem addition-trapping protocols allow for accessing highly substituted pyrones in a single operation with high selectivity.Radical reactions are well suited for the formation of multiple bonds in a single operation. 1,2 We have recently demonstrated that g-pyranones such as pyromeconic and kojic acid derivatives undergo highly efficient conjugate radical additions. 3 We have been interested in extending this chemistry to the functionalization of b-pyranones ( Figure 1). In an account in 2000, Feringa and co-workers had shown that ethyl radical derived from diethylzinc/oxygen adds to 1 (R = Ph) in good yield and selectivity. 4 In this work we demonstrate that a wide range of nucleophilic radicals participate in conjugate addition to readily available b-pyranones 1 in good yield and high diastereoselectivity. Furthermore, tandem protocols, i.e. radical addition-allyl stannane trapping, also proceed in good yield and selectivity to provide 2. The present methodology allows for the preparation of highly functionalized pyranones 4 in enantioenriched form. 5