1H-Tetrazoles possess the lowest pK a within the azole family of nitrogen-containing heterocycles, making them attractive amphoteric moieties for anhydrous proton conduction. The synthesis of a styrenic, random coil polymer with pendent C-substituted 1H-tetrazoles is described in detail. This facile route results in a polymer containing free proton-bearing tetrazoles, limits side reactions, and proceeds using low polarity, halogenated solvents (e.g., 1,2dichlorobenzene or chlorobenzene), which improve solubility during tetrazole cyclization. The resulting polymer, when probed by NMR spectroscopy and elemental analysis, had no measurable salt content, ensuring accurate proton conductivity measurements. Utilizing interdigitated electrodes (IDEs) in conjunction with electrochemical impedance spectroscopy (EIS), undoped anhydrous proton conductivities were measured to be as high as 10 −5 S cm −1 at 120 °C. This weakly acidic, 1H-tetrazole-bearing polymer is thermally stable to 210 °C, possesses two distinct glass transitions (T g ) at 49 and 74 °C, and exhibits surprisingly low water uptake, despite its acidic and amphoteric nature. Reduction of T g s, achieved by synthesis of low molecular weight poly(4-vinylphenol) via acid polymerization, shows a minimal dependence of anhydrous proton conductivity on backbone motion.
Blended resins were prepared from the resorcinol-based PEEK-like oligomeric phthalonitrile resin (RES) and tetrakis(phenylethynyl)benzene (TPEB), a high char yield arylacetylene resin. Initial probing of curing properties using differential scanning calorimetry, indicated that TPEB and RES co-cure when heated. Characterization of thermal properties using thermogravimetric analysis indicated that a 1:1 TPEB-RES blend (by weight) exhibited a char yield of 80% which was 6% larger compared to pure RES (74%). According to FTIR characterization, the enhanced thermal properties of TPEB-RES were the result of increased crosslinking density. Rheological studies of TPEB, RES, and TPEB-RES blends indicated that blended systems exhibit similar processing characteristics as RES resin. For example, resins display ideal viscosities and relatively large processing windows when cured at 175 C. Alternatively, pure TPEB resin exhibits low viscosities when melted, which are not suitable for preparing composite materials. This study indicates that preparing TPEB-RES blends is an effect strategy for improving thermal performance of potential RES composites while still maintaining the required processability for fabrication of dense polymer composites.Additional supporting information may be found in the online version of this article.
Force modulation microscopy (FMM) is a mode of scanning probe microscopy that can be used to visualize changes of tip−sample interactions for hard and soft areas of samples such as polymers and organic thin films. In designed experiments, polystyrene-encapsulated cobalt nanoparticles were imaged with FMM using a home-built sample stage for sample actuation. Regions of the outer polymer coating and the inner cobalt nanoparticle were resolved with high resolution. Using FMM, differences in the elastic and viscoelastic properties of the nanoparticles were visualized with nanoscale resolution by monitoring the return amplitude and phase signals as the AFM tip is scanned over areas of a sample. Regions of the sample with greater elasticity and viscoelasticity generate a weaker signal relative to harder areas because more of the energy associated with the cantilever oscillation is dissipated by the material. Areas with greater elasticity will tend to absorb more of the energy of the cantilever causing the amplitude of the oscillation to be dampened. Conversely, harder areas, having a lower elasticity, will cause the tip to oscillate closer to the input driving amplitude of the piezoceramic. The polymer-encapsulated nanoparticles were patterned using two-particle lithography to prevent aggregation of the nanoparticles.
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