Electrical properties of conventional polyimide films: Effects of chemical structure and water uptake

Counterion-Induced Control of the Colloidal State of Polyamic Acid Nanoparticles for Electrophoretic Deposition

Optimizing the colloidal state of polyamic acid (PAA) nanoparticles is essential for achieving a uniform and high-performance polyimide coating by electrophoretic deposition (EPD) on metal substrates of various shapes. In this paper, we report two important roles of the counterions in the formation of PAA colloids for EPD, which, to date, have not been recognized. First, when tertiary alkyl amines are used to neutralize PAA, the polarity of neutralizing counterions determines the size and stability of the PAA colloidal particles. The polarity can be finely tuned by using two different tertiary alkyl amines containing polar and nonpolar groups and adjusting the molar ratio. Depending on the polar/nonpolar ratio, various states of PAA colloids were obtained, including dissolved state, stable colloid, and aggregates. Second, we observed that the confined counterions inside PAA nanoparticles can act as an imidization catalyst during the thermal annealing process. It is revealed that some fraction of the counterion species, mostly having nonpolar groups, is not drawn toward the counter electrode and remains inside the PAA nanoparticles during the EPD process. Optimizing the polarity eventually allowed us to form uniform EPD coatings with high dielectric strengths.

Phosphine oxide based polyimides: structure–property relationships

The PI flame retardance has been influenced by the variation of flexible segments leading to a reduction of THR.

Dielectric and gas transport properties of highly fluorinated polyimides blends

The physicochemical properties of highly fluorinated polyimide blends were studied in order to highlight the advantages of employing a high content of fluorine atoms to tailor the properties of polyimide materials. Thus, dynamo-mechanical analysis was used to evidence the physical phenomena taking place during heating. The trend of storage modulus, loss modulus and loss factor tangent with temperature during and after the α relaxation was explored. The dielectric spectroscopy was carried out to investigate the dielectric behaviour at different temperatures and frequencies and to evaluate the values of dielectric constant, dielectric loss and electrical resistance. The dielectric spectroscopy data were corroborated with the dynamo-mechanical analysis to highlight the sub-glass transitions encountered in these blend films. Dielectric loss diagrams showed sub-glass transitions in the form of γ and β relaxations mainly due to the segmental mobility of the polymer chain components. The gas separation performance of some of the investigated blends was assesed, and their ability to achieve simultaneously higher gas permeability and higher selectivity was demonstrated.

Polyimides containing cycloaliphatic segments for low dielectric material

New polyimides have been synthesized by the reaction of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) or/and 5-[2,5-(dioxotetrahydrofuryl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) with 4,4′-methylene dianiline (DDM). Polycondensation reactions were carried out in N, N-dimethylformamide solution and the resulting polyimides gave flexible free-standing films. The introduction of alicyclic moieties in the polyimide backbone improved the solubility of the resulting polymers and facilitated their processing while maintaining a high thermal stability. The dielectric constant values (measured at 106 Hz at room temperature), were found in the range of 3.14–2.83 and decreased with increasing of the alicyclic units content.

Copolyimides containing perylene and hexafluoroisopropylidene moieties

Three poly(ether-peryleneimide)s were prepared by one-step solution polycondensation reaction at high temperature of an aromatic diamine containing an oxadiazole ring and/or diphenylether units with a mixture of perylenetetracarboxylic dianhydride and hexafluoroisopropylidene-diphthalic dianhydride. The structure of the polymers was confirmed by Fourier transform-infrared analysis. These polymers possess good solubility in N-methylpyrrolidinone and can be processed into thin and tough flexible films. They are highly thermostable, up to 465°C, and display glass transition in the range of 227–266°C. The dielectric constant values of these polyimides at 25°C and in the frequency domain of 1 Hz to 100 kHz are in the range of 2.29–2.96. The photoluminescence spectra of those poly(ether-peryleneimide)s consist of the emission of perylenediimide chromophore and conjugated segments containing five-imide rings, without the emission from oxadiazole chromophore.