Structure – promoted high performance properties of triphenylmethane - containing polyimides and copolyimides

Novel triphenylmethane-based polyimides and copolyimides were synthesized by polycondensation reaction of 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) with a triphenylmethane-based diamine, or an equimolar mixture of 4,4′-oxydianiline and triphenylmethane-based diamine, via conventional two-step procedure. Three novel diamines were developed as well, being obtained from ortho-toluidine and one of the following aldehydes: benzaldehyde, 4-bromobenzaldehyde or 4-fluorobenzaldehyde. The relationship between the macromolecular structural motif and physical properties of the synthesized polymers was investigated in detail, with emphasis on thermal transitions and stability, dielectric behavior, molecular disorder, mechanical toughness and gas separation performance. The amorphous, free-standing, tough and defectless films prepared from these polymers showed excellent thermal stability, their decomposition starting above 425 °C. For all polymer films which were subjected to dielectric properties measurements, the variation of the real and imaginary parts of the dielectric permittivity with frequency and temperature was measured and discussed. The values of the dielectric constant and dielectric loss were measured at room temperature and in the frequency domain from 1 Hz to 1 MHz, and the obtained results proved the beneficial effect of fluoro and bromo graphting on the dielectric constant reduction. The dielectric spectroscopy data showed distinct γ and β subglass transitions at lower activation energies for copolyimides compared to polyimides, suggesting that the incorporation of the co-monomer diamino-diphenyl ether allows faster motions of the small molecules, but hinders the mobility of charge carriers. The permeability of several gases through these membrane-forming materials were measured and discussed with respect to the structural variations in the polymer repeating unit.