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AbstractThe IR spectra of glassy polymers were studied in the terahertz range 0.27 − 6 THz (9–200 cm−1), where absorption appears due to both individual and collective torsional (libration) vibrations preceding the manifestation of relaxation dynamics. It is shown that collective torsional-vibrational modes, caused by the correlation of librational vibrations in a section of the chain commensurate with its thermodynamic segment, are responsible for the excess density of vibrational states at terahertz frequencies in the IR spectra of glassy polymers. [ABSTRACT FROM AUTHOR]

The temperature dependence of low-frequency IR spectra of glassy polymers in the range ν = 0.24–4 THz (8–135 cm−1) at temperatures from 90 to 400 K has been studied. Their analysis made it possible to detect absorptions corresponding to both individual and correlated torsional vibrations, which couple to the manifestation of relaxation dynamics. The temperature evolution of IR spectra at terahertz frequencies shows 3 universal features: low-temperature, corresponding to the anharmonicity of torsional-vibrational motion, high-temperature, due to the contribution of the α-relaxation (glass transition), and intermediate, associated with unfreezing of the conformational mobility of chains during the β-transition. The results obtained were shown to be applicable to polymers with both hydrogen and van der Waals bonds between the macromolecules. [ABSTRACT FROM AUTHOR]

The aim of this research was the detailed analysis and estimation of CER oligomer‐based nanocomposites for applications under extreme high temperature conditions. Thermostable nanocomposites based on cross‐linked cyanate ester resin (CER), derived from PRIMASET PT‐30 multi‐functional oligomer and doped by 0.025wt% to 10wt% epoxycyclohexyl‐functionalized polyhedral oligomeric silsesquioxane (ECH‐POSS) nanoparticles, were synthesized and characterized using TEM, mid‐, and far‐IR spectroscopy, and by DMA, DSC, CRS, and TGA techniques. At nanoparticles contents less than 1wt%, basically their molecular level dispersion in the matrix is suggested, whereas their clusters of about 20 to 30 nm in diameter were observed at 2wt% and 10wt% ECH‐POSS. In correlation with the results of structural analysis, the ambivalent influence of the nanoparticles, depending on their content, on the dynamics and properties of nanocomposites was revealed. The "constrained dynamics" effects caused by post‐curing and covalent embedding ECH‐POSS units into the matrix were registered by DMA, far‐IR spectroscopy and CRS. Highly cooperative glass transition with Tg ≈ 400°C (DMA, 1 Hz) was observed, and at the limit total suppression of glass transition could be achieved. The obvious superiority of the studied nanocomposites over the CER nanocomposites synthesized from monomeric dicyanate ester of bisphenols, especially at high temperatures, was shown. [ABSTRACT FROM AUTHOR]

Thermostable densely crosslinked cyanate ester resins (CER) with different chemical structures, derived from monomer dicyanate esters of bisphenol E (DCBE), bisphenol A (DCBA), hexafluorobisphenol A (6F-DCBA) or from cyanated phenol-formaldehyde oligomer PT-30, and the nanocomposites based thereon, with 0.01 to 10 wt% epoxycyclohexyl-functionalized polyhedral oligomeric silsesquioxane (ECH-POSS), were synthesized and characterized by means of dynamic mechanical analysis, differential scanning calorimetry, far-infrared, and creep rate spectroscopy techniques. As shown, thermal and mechanical properties increased in a row of matrices prepared from DCBE < DCBA < 6F-DCBA < PT-30. Thus, these matrices with Tg = 248, 275, 300, and ~400°C (DMA, 1 Hz), respectively, had dynamic modulus E′ values of 1.8, 2.7-3.0, and 3.6 GPa at 20°C; high rigidity (dynamic modulus of about 1-2 GPa) retained at temperatures up to 200°C for DCBE matrix, 250°C for DCBA and 6F-DCBA matrices, but up to 380°C for PT-30-based matrix. The maximal effects from introducing ECH-POSS nanoparticles, covalently embedded into CER network, were attained mainly at their ultra-low contents (<<1 wt%); however, the ECH-POSS impact decreases in a row of matrices prepared from DCBE > DCBA > 6F-DCBA > PT-30. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]