Optical Properties of Some New Azo Photoisomerizable Bismaleimide Derivatives

Novel polythioetherimides bearing azobenzene moieties were synthesized from azobismaleimides and bis-2-mercaptoethylether. Kinetics of trans-cis photoisomerization and of thermal conversion of cis to trans isomeric forms were investigated in both polymer solution and poly(methyl methacrylate) doped films using electronic absorption spectroscopy. Thermal recovery kinetics is well described by a two-exponential relation both in solution and polymer matrix, while that of low molecular weight azobismaleimide fit a first-order equation. The photoinduced cis-trans isomerization by visible light of azobenzene chromophores was examined in solution and in polymer films. The rate of photoinduced recovery was very high for azobismaleimides

Novel Bio-Based Materials: From Castor Oil to Epoxy Resins for Engineering Applications

The paper presents the synthesis and thermal behavior of novel epoxy resins prepared from epoxidized castor oil in the presence of or without trimethylolpropane triglycidyl ether (TMP) crosslinked with 3-hexahydro-4-methylphtalic anhydride (MHHPA) and their comparison with a petroleum-based epoxy resin (MHHPA and TMP). Epoxidized castor oil (ECO) was obtained via in situ epoxidation of castor oil with peroxyacetic acid. The chemical structures of castor oil (CO), ECO, and epoxy matrix were confirmed using FT-IR and 1H-NMR spectroscopy. The morphological and thermal behavior of the resulting products have been investigated. Compared to petroleum-based resins, castor oil-based ones have a lower Tg. Anyway, the introduction of TMP increases the Tg of the resins containing ECO. The morphological behavior is not significantly influenced by using ECO or by adding TMP in the synthesis of resins. The dielectric properties of epoxy resins have been analyzed as a function of frequency (1 kHz–1 MHz) and temperature (−50 to 200 °C). The water absorption test showed that as Tg increased, the percent mass of water ingress decreased

Synthesis and Characterization of a New Thermoreversible Polyurethane Network

A new polyurethane network was synthesized by the Diels–Alder cross-linking reaction of a polyurethane to bisfuryl monomer. Attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR-FTIR) spectra of the network showed the disappearance of the absorption bands of maleimide and the appearance of new bands attributed to furan-maleimide cycloadduct. Chemical shifts characteristic to the cycloadduct appeared in the proton nuclear magnetic resonance spectra. ATR-FTIR and differential scanning calorimetry (DSC) demonstrated the thermal reversibility of the material by the reproduction of the retro-Diels–Alder and Diels–Alder processes upon heating and cooling. Global kinetic nonisothermal decomposition parameters in nitrogen were determined by the Flynn-Wall-Ozawa method. A three successive stage thermal decomposition mechanism depicted by <i>n</i> order reaction model for each stage was proposed. The validity of the chosen kinetic model and the values of the kinetic parameters of the individual decomposition stages were determined by the multivariate nonlinear regression method