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The relaxation behavior of polyimide and its nanocomposite containing 10 wt % of graphene was studied by using the dynamic mechanical spectrometer. Dynamic mechanical analysis of polyimide and its composite was performed as a function of temperature and frequency in the temperature range of 25-480 8C and frequency range between 0.05 and 100 Hz. The effect of increasing frequency of testing from 0.05 to 100 Hz is a significant shift from the glass transition temperature, T g , to higher temperature from 360 8C at 0.05 Hz to 420 8C at 100 Hz. The tan d peak height for both a and b transitions decreased with increasing test frequency from 0.24 at 0.05 Hz to 0.08 at 100 Hz, due to increasing restriction to chain motion. At any given testing frequency, the T g for the composite was shown to be higher than that for the matrix by about 5-10 8C. The Arrhenius equation was used to calculate the activation energy for both a and b transitions. The activation for a and b transitions for the composite and polyimide matrix were determined to be 688 and 537 kJ/mol and 313 and 309 kJ/mol, respectively, indicating that a significant increase in the energy barrier to chain relaxation occurred as a result of reinforcement of polyimide with low weight fraction of graphene. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43684.

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In this study, poly(o-anisidine) [POA], poly(o-anisidine-co-aniline) [POA-co-A], and polyaniline [PANi] were chemically synthesized using a single polymerization process with aniline and o-anisidine as the respective monomers. During the polymerization process, ptoluene sulfonic acid monohydrate was used as a dopant while ammonium persulfate was used as an oxidant. Nmethyl-pyrolidone (NMP) was used as a solvent. We observed that the ATR spectra of POA-co-A showed features similar to those of PANi and POA as well as additional ones. POA-co-A also achieved broader and more extended UV-vis absorption than POA but less than PANi. The chemical and electronic structure of the product of polymerization was studied using Attenuated Total Reflectance spectroscopy (ATR) and UV-visible spectroscopy (UV-vis). The transition temperature of the homopolymers and copolymers was studied using differential scanning calorimetry and the viscosity average molecular weight was studied by using dilute solution viscometry.

Polyimide-graphene composites were synthesized by in-situ condensation polymerization and the thermal stability and decomposition behavior of the composites were studied. Polyimides, because of their aromatic backbone, are a class of fire-retardant polymers. Their high char retention ≥50% at testing temperatures ≥600 °C makes them thermally stable polymers. The effect of nanographene sheets on the decomposition behavior of polyimide is presented in this paper. It is shown that the reinforcement of polyimide with nanographene sheets significantly decreased the rate of decomposition of polyimide and increased the char retention of the composite. Thermogravimetric analysis data were used to assess the thermal stability, rate of mass loss and predicted limiting oxygen index of the neat polyimide and composites. Results obtained showed around a 43% decrease in the rate of polyimide degradation at 50 wt.% graphene loading. The limiting oxygen index of the polyimide nanocomposite was calculated by using the char retention, and it was found to increase by up to 24% at 50 wt.% graphene loading over that for the neat matrix.