Rohit H. Vora

Gas transport properties of 6FDA-durene/1,4-phenylenediamine (pPDA) copolyimides

We have determined the gas transport properties of He, H2, O2, N2, and CO2 for 6FDA-durene homopolymer and 6FDA-durene/pPDA copolyimides. The 6FDA-durene exhibits the highest permeability with the lowest selectivity. Permeability of copolymers decreases with increasing 6FDA–pPDA content, while permselectivity increases with an increase in 6FDA–pPDA content. 6FDA-durene/pPDA (50/50) and 6FDA-durene/pPDA (20/80) materials have O2 and CO2 permeabilities greater than those calculated from the addition rule of the semilogarithmic equation. These higher deviations from the additional rule of the semilogarithmic equation are mainly attributed to the fact that these copolyimides have higher solubility coefficients than those calculated from the additive rule. The Tg s of 6FDA-durene/pPDA copolyimides decrease with an increase in 6FDA–pPDA content. Tg s predicted from the Fox equation are lower than the experimental data, and the their difference increases with an increase in pPDA content, implying the copolyimides of 6FDA-durene/pPDA may have greater interstitial space among chains because of the conformation difference, and thus create more fraction free volume compared with the ideal case of simple volume addition. Density measurements also suggest these two copolymers have greater free volumes and the fractions of free volume, which supporting the gas transport results. The thermal stability and β-relaxation temperature have also been studied for these copolymers.

Kinetics of thermal degradation of 6FDA based copolyimides—I

Abstract Two series of linear aromatic copolyimides containing hexafluoro isopropylidine moieties (i.e. 6F) were synthesized by reacting 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) with various mole percents of 2,3,5,6-tetramethyl-1,4-phenylene diamine (Durene diamine) and 2,6-diamino toluene (DAT) or m-phenylene diamine (mPDA) in N-methyl-2-pyrrolidone (NMP). These copolyimides were characterised by GPC, XRD, DSC, TMA, DMA and TGA. Copolymer composition of these copolyimides was determined using 1H-NMR. Tg calculated using Fox equation was compared with experimentally found values. All copolyimides were found to be amorphous. Activation energy was determined for the thermal degradation of these copolyimides using Coats–Redfern and Chang equations and were found to follow first order kinetics in air and in nitrogen. Inherent viscosity and Tg, decreased with decrease in mole ratio of durene diamine whereas activation energy and frequency factor [ln (A)] were found to increase with decrease in mole ratio of durene diamine in [6FDA+Durene diamine+mPDA] and [6FDA+Durene diamine+DAT] copolyimide series. CO2 was the main decomposition product in air and CHF3 in nitrogen atmosphere. Amount of CHF3 evolved increased with increase in durene content in copolyimide series.

Molecular mass determination of polyamic acid ionic salt by size-exclusion chromatography

A methodology was developed for the determination of molecular weight aveages of polyamic acid ionic salt (PAS) by size-exclusion chromatography (SEC). Polystyrene standards were used for calibration and THF-DMF 1:1 by volume containing 0.06 M LiBr and 0.06 M H3PO4 was used as the mobile phase. The proposed methodology was found to be reproducible.

Thermal degradation kinetics of 6FDA/durene diamine/pPDA copolyimides

Abstract Aromatic copolyimides have been synthesised from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) with various mol-% of 2,3,5,6-tetramethyl-1,4-phenylene diamine (durene diamine (DDA)) and 1,4-phenylene diamine (pPDA) in N -methyl-2-pyrrolidone (NMP). Copolyimides were characterised by inherent viscosity, GPC, DSC, DMA, XRD, and TGA. Inherent viscosity and molecular weight increased with increase in DDA content in copolyimides. This was attributed to higher basicity of DDA than pPDA, which resulted in higher reactivity towards dianhydride. They were found to be soluble in all common solvents except CCl4 and methanol. The glass transition temperature T g of these amorphous copolymers increased with increase in DDA content; T gs determined by DSC and DMA were comparable and T g calculated using the Fox equation was compared with the experimental value. Thermal degradation of these copolyimides was found to follow second order kinetics in air. The activation energy E a for the thermal degradation of these copolyimides in air was determined by both the Coats-Redfern and Chang methods and the result was comparable. Both Ea and ln A were found to decrease with increase in DDA content; CO2 and trace amounts of CHF3 were the decomposition products. The mechanism of thermal degradation is unique and is not affected by a change in the copolymer composition because all copolyimides display the kinetic compensation effect.