Copolyimides containing alicyclic and fluorinated groups: Characterization of the film microstructure

Abstract

The microstructures of a series of copolyimide films were characterized with different experimental methods such as density measurements, X-ray diffraction, ultraviolet-visible spectrophotometry, positron annihilation spectroscopy, and dynamic mechanical analysis. The experimental data were linked to the chemical structures of the polymers and especially the alicyclic and fluorinated monomers. Some analysis responses were directly dependent on the fluorine atoms and, therefore, did not provide clear information about the microstructures. The chain organization in the amorphous films appeared to be significantly dependent on the effect of the casting solvent. The influence of the alicyclic group content was quite significant for a nonsubstituted diamine but was strongly attenuated with a fluorinated diamine.

Molecular Dynamics Simulations of Helium Permeation in Polyimides with a Bulky Dianhydride and a Fluorinated Diamine

“…The latter case is presented in details in Figure 5, so as to characterise the morphology of the polyimide experienced by the probe. The relative order of % PAV is consistent with S c and in good agreement with the free‐volume fractions ( FFV ) empirically estimated from the experimental densities using the Bondi method 29, 73. It is clear that the systems with the lowest PAV, that is, the ODPA‐ODA and the unsubstituted copolymer, are also highly deficient in terms of small holes.…”

“…It should be noted that while we tested the case of a CF 3 group on the diamine, similar results are seen experimentally if fluorinated units are introduced on the dianhydride 3. While the associated experimental study found approximately similar permeability coefficients for the BCDA‐ODA homopolyimide and the fluorinated (ODPA/BCDA)‐CF 3 ODA copolyimide with 20% BCDA (Table 4), results for the latter were found to be dependent on the choice of the solvent, and no reproducibility for the former was tested 29. It seems likely that the one with the largest FFV and a wider distribution of free volume holes (i.e., the fluorinated copolyimide) should be slightly better, something which is seen in the simulations.…”

“…The diamines were the 4‐4′‐oxydi(phenylamine) (ODA) and 2‐trifluoride‐4‐4′‐oxydi(phenylamine) (CF 3 ODA), respectively. In parallel, these polyimides were synthesized and their microstructures and gas permeation properties were characterised experimentally 28–30. Model and real systems were shown to be in excellent agreements in terms of densities, solubility parameters, d‐spacings, colour indices and free‐volume fractions 27.…”

Influence of System Size in Molecular Dynamics Simulations of Gas Permeation in Glassy Polymers

“…Table 2 shows the average relaxed densities 〈F〉, which are all very close to the experimentally determined value of F exp ) 1.368 g cm -3 . [19][20][21] The average pressures of the simulation boxes, 〈p〉, prove that these densities correspond to atmospheric conditions. 〈F〉 for the 4150-atom systems is almost identical to F exp whereas the 6225-atom and 56025-atom systems fall within 0.7% of the experimental value.…”

A molecular dynamics simulation study of surface effects on gas permeation in free-standing polyimide membranes

“…However, their permeation properties are strongly affected by the considerable number of parameters that can influence diffusion, selectivity or other physical properties over the entire processing stage [4][5][6][7][8]. Polyimide membranes are often prepared by the so-called "solvent casting method", in which they are cast on a substrate from solutions prepared by dissolution of the polyimide into a solvent such as m-cresol or N-methylpyrrolidone [9]. Different casting surfaces will potentially lead to different properties.…”