In this work, we report on the thermal stability of nanohybrid polyurethane (PU)/polyhedral oligomeric silsesquioxanes (POSS) elastomers analyzed by evolved gas analysis (EGA). Functionalized POSS ...were chemically introduced into PU structure as pendant groups (1,2-propanediolizobutyl POSS (PDI-POSS), disilanollsobutyl POSS (DSI-POSS)) or as chemical crosslinks (octa(3-hydroxy-3-methylbutyldimethylsiloxy) POSS (OCTA-POSS)).
EGA results of the thermal degradation of the PU/POSS hybrid elastomers have demonstrated that the hybrid systems are slightly more thermally stable when compared to the unmodified PU matrix, as evidenced by reduced amounts of volatile degradation products. It was found that the thermal decomposition of polyurethane materials reinforced with POSS starts from about 300 °C via urethane bonds breakage. In lower temperature region the modified polyurethanes decompose to some low molecular weight compounds and intermediates with hydroxyl and amine groups. At temperatures above 350 °C evolution of hydrocarbons, aldehydes, alcohols, amines, cyclic species and low molecular weight compounds - carbon monoxide, carbon dioxide, water and ammonia was recorded.
Furthermore, the inclusion of POSS in the PU network directly influences the degradation pathways of both the soft and hard block components of the elastomers – it has been observed that the POSS/PU hybrid systems show reduced levels of CO2 and changed levels of characteristic ion fragments, e.g. m/z 42 related to hydrocarbons and THF.
•Thermal behavior of polyurethane elastomers was elaborated by hyphenated techniques.•Non-oxidative atmosphere facilitates alkyl and carbonyl compounds formation upon decomposition.•POSS presence influences the degradation mechanism of polyurethane elastomers.•General scheme of thermal degradation for polyurethane under oxidative atmosphere is presented.
We report for the first time on a polyurethane system with polyhedral oligomeric silsesquioxanne (POSS) particles chemically bonded along its main chain as nanobuilding blocks. Morphology and ...molecular dynamics of this novel system are studied with imaging (SEM), thermal (DSC, MDSC) dielectric (TSDC, DRS), and mechanical (DMA) techniques. Two distinct phases occur: one chain extended with POSS and one with chemistry and morphology similar to the matrix. Although T g remains practically unaffected upon incorporation of particles, a relaxation α′ slower than the main dynamic glass transition α and present also in the matrix is enhanced in the presence of POSS. We attribute it to decelerated dynamics in the presence of heavy moieties like particles and rigid hard microdomains. No effect on the time scale of these relaxations is imposed by the presence of POSS, but rubbery modulus is significantly reduced due to the soft POSS-extended phase.
Polyhedral oligomeric silsesquioxane moieties with poly(ethylene glycol) groups attached on the cage (PEG–POSS) were blended with an elastomeric polyurethane matrix, in contents up to 10 wt %. ...Several experimental techniques in agreement with each other show that the PEG–POSS moieties disperse well on the molecular level and act as diluents plasticizing the molecular dynamics. Although the degree of microphase separation is only weakly affected in all the compositions, changes in the macromorphology related to the POSS moieties have an impact on the matrix properties, decreasing the storage modulus. The PEG–POSS themselves display segmental dynamics, glass transition, and crystallinity; however, none of these properties are observed in the blends, providing additional support for excellent miscibility with the matrix. The results are compared to those of previous works where different synthesis approaches resulting in different POSS topologies were used.
Octa-OH-functional POSS has been incorporated into a model polyurethane elastomer as a comparatively massive and notionally “robust” 3-dimensional cross-linking core. The effects of this ...cross-linking moiety on the morphology and molecular dynamics of the system are studied over a range of size and time scales. Microscopy, scattering, spectroscopic, thermal, and dielectric techniques, in agreement with each other, show that the covalent inclusion of the cross-linking particles restricts microphase separation, inhibits the formation of hard-block domains, and decelerates the motional dynamics of the polyurethane backbone. The effects on both the morphology and the dynamics of the polyurethane system are not continuous but occur in a steplike manner in the loading region of 4–6 wt % POSS. This critical region is thought to correspond to a sterically induced transition from one dominant morphology (microphase segregated) to an increasingly homogeneous nanophase segregated domain morphology. Contrary to expectations, cross-linking, even by the presumably rigid siliceous nanoparticles, reduces the mechanical modulus. In conjunction with the reduction of microphase separation, this observation indicates that the hard microdomains reinforce the polymer more effectively than the chemical cross-links.
Reported here is the synthesis and thermal characterization of a series of polyhedral oligomeric silsesquioxane (POSS) modified polyurethane elastomers. A novel polyurethane architecture has been ...synthesized which incorporates a partially opened POSS-diol cage (disilanolisobutyl POSS) directly into the methylene di-isocyanate/poly(tetramethylene) glycol urethane network as a substitute chain extender moiety without the need for an alkyl tether. The effects of the inclusion of a sterically hindered and rigid silsesquioxane cage structure on both the non-oxidative thermal stability and micro-phase segregated morphology of the resultant polyurethane elastomer have been studied extensively over a range of POSS inclusion levels by means of pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) and differential scanning calorimetry (DSC). The results of analytical pyrolysis assays of the polyurethane systems clearly demonstrate that low levels of POSS substitution (<10 wt. %) lead to a significant increase in both the onset temperature of thermal de-polymerization and a reduction in the yield of volatile degradation products. A characterization of the products of degradation demonstrate that the POSS modified elastomers show some subtle differences in thermal degradation mechanism, yielding increased levels of propenal and decreased levels of ethane when compared with an unmodified control. POSS inclusion enhances the hard-block crystallinity at low levels and DSC analysis demonstrates that the peak thermal stability of the systems corresponds with a maximum in hard-block crystallinity (at a level of 4–6 wt. % POSS). At higher mass fractions we observe a breakdown in the phase separation of the systems and a decline in hard-block crystallinity, which correlates with an observed decrease in the primary onset degradation temperature. The major mechanistic pathways of degradation (urethane bond depolymerisation followed by secondary radical degradation of the monomers) have been shown to be insensitive to the presence of POSS in the matrix. Rather, it is physical changes in the morphology of the elastomer systems, as a consequence of POSS inclusion that are responsible for the observed improvements in the thermal stability of these materials.
Refractive index dispersion of thin films of deoxyribonucleic acid (DNA)-surfactant (CTMA) and doped DNA-CTMA-Nile Blue (NB) (5 w%) complexes are reported and discussed. The thermal variation of the ...thin film thickness was measured by ellipsometry. The DNA-CTMA complex exhibits a rarely observed negative thermal expansion between room temperature and ca. 85°C. Doping with NB decreases the temperature range of negative thermal expansion to between room temperature and ca. 70°C. The dopping by 5 w% of NB lowers the absolute value of negative thermal expansion of DNA-CTMA system from 5% to 2% within this temperature range.
In this chapter are described properties of DNA complexes with originally proposed cationic surfactants in view of organic electronic applications. Properties of prepared complexes were studied with ...help of UV-vis-NIR and FT-IR spectroscopies, TGA and DSC analysis and X-ray diffractometry.
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