Search

Epoxy (EP) was copolymerized with polyamic acid (PAA, precursor of polyimide (PI)) with termanil monomers of (1) 4,4′-Oxydianiline (ODA) and (2) pyromellitic dianhydride (PMDA) individually to form (PI-O-EP) and (PI-P-EP) copolymers. The FTIR spectrum of PI-O-EP copolymerization intermediates shows that some amide-EP linkages were formed at low temperature and were broken at higher temperature; in additoin, the released amide was available for subsequent imidization to form PI. The curing and imidization of the amide groups on PAA were determined by reaction temperature (kinetic vs. thermodynamic control). In PI-P-EP, the released amide group was very short-lived (fast imidization) and was not observed on FTIR spectra. Formation and breakage of the amide-EP linkages is the key step for EP homopolymerization and formation of the interpenetration network. PI contributed in improving thermal durability and mechanical strength without compromising EP's adhesion strength. Microphase separations were minimal at PI content less than 10 wt%. The copolymerization reaction in this study followed the "kinetic vs. thermodynamic control" principle. The copolymer has high potential for application in the field of higher-temperature anticorrosion. [ABSTRACT FROM AUTHOR]

A novel type of polyimide foams (PIFs) with chemically inserted flexible aliphatic diamine (1,6-diaminohexane (HMDA)) segments was successfully synthesized and characterized in this research. The aliphatic HMDA segments were randomly incorporated in the long chain aromatic imide bonds. The obtained PIFs containing various HMDA contents (0 to 20 mol%) exhibited different morphologies such as lowered density and larger cell diameter (with higher HMDA content), and open cell ratio was increased as well. HMDA rendered flexibility to the copolymer leading to decreased rigidity. Compared to using 4,4 ′ -oxydianiline (ODA) as the sole diamine source, incorporating low cost of HMDA would increase the PIF's flexibility and improve its processibility while making the production more cost effective. Within some range of compromised thermal and mechanical properties, this proposed method could be feasible for industrial applications. [ABSTRACT FROM AUTHOR]

A facile methodology has been developed to synthesize silver-filled multiwalled carbon nanotubes (S-MWNTs)-polyimide (PI) nanocomposites with high thermal conductivity for applications in flexible printed circuits or buried film capacitors, requiring efficient heat dissipation. MWNTs functioned as modules to facilitate the distribution of Ag particles within PI matrix. The intercalation of Ag within MWNTs was performed using capillary action upon mixing AgNO3 solution with PI precursor and followed by calcinations to reduce the ionic silver to Ag. The existence of Ag in the PI nanocomposites was observed from transmission electron microscope images and verified with the energy-dispersive X-ray spectrometer. Homogeneous dispersion of SMWNTs in PI matrix and strong interaction between S-MWNTs and PI were also suggested by SEM cross-section images. The thermal conductivity of S-MWNT/PI nanocomposite was a function of the content of S-MWNTs in PI matrix. The PI nanocomposite containing 1.5 wt % of S-MWNTs (S-MWNT/PI-1.5) exhibited the highest thermal conductivity, 0.37 W/mK. A decrease in thermal conductivity was observed while the surface roughness of the nanocomposite was higher than 1 μm owing to the high content of S-MWNT in PI. In addition, the modified MWNTs improved flexibility of the PI matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

The silane-modified, acid-treated carbon nanotubes (silane-modified HCNTs) were prepared using acid-treated carbon nanotubes (HCNTs) and octyltriethoxysilane (OTES) via the sol–gel process. The silane-modified HCNTs and the HCNTs were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and transmission electron microscopy (TEM). The Raman spectra showed that there were larger reactive sites on nanotubes treated in the H2SO4/HNO3 mixture acid for 2 h. The chemical structural effects on the morphology, dispersion, and thermal and emission properties of the carbon nanotube emitter paste were investigated by scanning electron microscopy (SEM), SEM mapping, ultraviolet–visible (UV–vis) spectrophotometry, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), emission pattern, and current–voltage curve measurements. The UV–vis spectrophotometry indicated that the silane-modified HCNTs could be stably dispersed in toluene over 96 h. It was found that the compatibility between silane-modified HCNTs and the matrix material was mainly due to the interpenetrating polymer network structure between them. The thermal stability of the silane-modified HCNT emitter paste was improved by increasing the content of silane-modified HCNTs. A homogeneous emission was observed when using the silane-modified HCNT emitter paste. The current density extracted from the sample with the silane-modified HCNT emitter paste was higher than that with the HCNT emitter paste at a constant voltage. The turn-on fields of 3 wt % silane-modified HCNT emitter paste and HCNT emitter paste were 1.9 and 5.6 V/µm, respectively. [ABSTRACT FROM AUTHOR]