Model ternary thiol−ene/acrylate photopolymerization involving acrylate homopolymerization and copolymerization of thiol−ene and thiol−acrylate monomers were monitored by real-time FTIR. In all ternary mixtures, including those prepared with different acrylate concentrations, acrylate conversion was 100%. However, thiol−ene conversions were found to be controlled by their initial concentrations. The influence of acrylate monomer chemical structure on the thermophysical properties of ternary thiol−ene/acrylate systems was studied with DMA, DSC, and the absorbance of a nondestructive impact energy. The addition of acrylate to the thiol−ene system increased the rubbery modulus while the tan δmax shifted to higher temperatures. Densely cross-linked, heterogeneous matrix formation was observed with the broadening of tan δ peaks at high acrylate concentrations. The high impact absorption of these ternary thermoset photopolymers was correlated with the dynamic mechanical damping ability of the networks. Acrylates with higher functionality and low molecular weight per double bond are more effective at increasing the glass transition temperature of the thiol−ene polymer network. Fracture behavior of ternary thiol−ene/acrylate networks under impact shows a dependence on the chemical structure of the acrylate, component concentrations, and low-temperature relaxation processes. The ternary matrix formed with a bisphenol A based difunctional acrylate monomer exhibited improved impact energy absorption at room temperature. Finally, tensile properties of polymer networks formed with thiol−ene/acrylate and thiol−acrylate mixtures are given for comparison purposes.

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Urethane-based multiene monomers were synthesized and photopolymerized with a trifunctional thiol monomer to form highly cross-linked thiol−ene networks. Real-time FTIR was used to monitor the conversion of thiol and urethane ene monomers as a function of irradiation time. For stoichiometric thiol−urethane ene photopolymerizations, monomers reacted in a 1:1 molar functional group ratio, reaching ∼90% monomer conversion within several seconds. The effects of the ene chemical structure and concentration on thermal and mechanical properties were characterized by DMA, DSC, TGA, tensile, and energy absorption upon nondestructive impact. The temperature at tan δmax of the thiol−urethane ene networks was around 39 °C and decreased to lower temperatures with the addition of a reactive diluent diallyl ether ene monomer. Tensile and impact results were combined with fracture toughness measurements to elucidate the effect of the urethane and bisphenol A chemical structures. The energy absorption was dependent on the glass transition temperature of the thiol−urethane ene cross-linked networks. Improvement in fracture toughness and tensile properties was observed with the incorporation of 10 mol % of an ene with a bisphenol A structure. Scanning electron micrographs of fractured surfaces were used to interpret the nature of the brittle fracture. All of the properties of the thiol−urethane ene networks were compared to a conventional trithiol−triallyltriazine trione-based matrix.

Photocurable, ternary‐component mixtures of a 1:1 molar multifunctional thiol–ene (trithiol and triallyl ether) blend and a 16‐functional acrylate based monomer have been photopolymerized, and the final film properties of the ternary crosslinked networks have been measured. The photopolymerization kinetics, morphology, and mechanical and physical properties of the films have been investigated with real‐time infrared, atomic force microscopy, and dynamic mechanical analysis. The photopolymerization process is a combination of acrylate homopolymerization and copolymerizations of thiol with allyl ether and acrylate functionalities. The tan δ peaks of the photopolymerized ternary systems are relatively narrow and tunable over a large temperature range. The morphology is characterized by a distinct phase‐separated nanostructure. The photocured thiol–ene/acrylate ternary systems can be made to exhibit good mechanical properties with enhanced energy absorption at room temperature by the appropriate selection of each component concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 822–829, 2007.

Non‐viral gene delivery agents are notorious for their poor nucleic acid transfection efficiency and relatively high cell cytotoxicity. Thus, many investigators are exploring the important parameters involved in charged polymer‐mediated gene delivery, such as chemical composition, molecular weight, structural architecture, surface charge, etc. It is important to develop clear structure‐property relationships in order to design successful nucleic acid delivery agents for gene therapy. To elucidate these relationships, well‐defined materials are necessary. Controlled radical polymerization methods offer a facile route to systematically produce well‐defined, structurally distinct gene delivery agents. The use of charged polymers prepared via controlled radical polymerizations to elucidate transfection mechanisms or develop new delivery vectors will be reviewed herein.magnified image