Molecular structure dependences of the coefficients of molecular packing (Kp) and the intrinsic birefringence (Δn0) were investigated for aromatic polyimides (PIs) using a method based on the modified Lorentz–Lorenz equation and the Vuks equation. This method needs only average refractive indices and polarizability tensors ( ) for PI repeating units. αˆ was calculated using the density functional theory at the B3LYP/6‐31+G(d) theory level that was confirmed as optimal for PI repeating units. Because bent or kinked structures in main chain hinder the ordering of polymer chains, Kp decreases in cases that ether linkages are introduced in the main chain and that kinked‐structured dianhydrides are used. Introduction of side groups, trifluoromethyl (CF3) groups in particular, also causes decreases in Kp. On the other hand, the estimated values of Δn0 are proportional to the calculated anisotropy in αˆ (Δα/Vvdw), thus Δn0 can be well predicted by computation. The values of Δα/Vvdw are decreased not only by bent structures in the main chain (e.g., ether linkage), presence of side groups, but also by large fractions of imide rings in the polymer structures. The estimated values of Δn0 range from 0.338 to 0.470, which are much larger than the reported ones for optically transparent conventional polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2354–2366, 2004

Degrees of orientation of main chains and imide rings were quantitatively estimated for spin‐coated films of six kinds of aromatic polyimides (PIs) using polarized attenuated total reflection (ATR)/Fourier transform infrared (FT‐IR) spectroscopy. The degrees of chain orientation parallel to the film planes are significantly larger for the PIs having rigid structures than those having flexible structures, and the introduction of side groups decrease the degrees of chain orientation. In contrast, the rotational orientations of imide rings are almost isotropic for all PI films. Moreover, the film thickness dependences of the degrees of orientation were investigated for two kinds of rigid‐rod PIs having bulky trifluoromethyl (CF3) side groups in their diamine moieties. The degrees of chain orientation slightly decrease as the film thickness increases, whereas the rotational orientation of imide rings is independent of the film thickness. The degrees of chain orientation on the substrate sides significantly differ from the atmospheric sides of PI films. This difference was generated during thermal imidization because of tensile stress originated from the mismatch in thermal expansion coefficients between the substrates and the PI films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2109–2120, 2005

New polyamide thin film composite membranes were prepared by interfacial polymerization of hexafluoroalcohol (HFA)-containing aromatic diamine and trimesoyl chloride (TMC) on a porous polysulfone support. The surface properties of the resulting membranes were characterized by water contact angle, XPS, and SEM. Additionally, the desalination separation performance was evaluated by the cross-flow filtration of 2000 ppm NaCl solution. Water contact angle and XPS analyses indicated that the HFA-containing polyamide membrane is relatively hydrophobic at neutral conditions but becomes hydrophilic at basic conditions due to ionization of the HFA groups, so we refer to this group as an ''ionizable hydrophobe'' or ''i-phobe''. The membrane showed strongly pH-dependent reverse osmosis behavior with enhanced performance (high water flux and high salt rejection) at high pH (ca. 10). Both the electron withdrawing nature and the steric bulkiness of the HFA functionality are also advantageous in protecting the polyamide membrane from chlorine attack. Based upon NMR studies of model polymers (linear polyamides with and without the HFA functionality) and the membrane performance measured before and after chlorine exposure, the HFA-containing polyamide has improved chlorine stability compared to the reference polyamide made from m-phenylenediamine and TMC.

Thermo-optic coefficients for TE-and TM-polarized lights (dn TE /dT and dn TM /dT; temperature gradient of refractive index) were measured for seven kinds of aromatic polyimide (PI) films formed on Si Substrates. The values of dn/dT for average refractive indices (dn av /dT) are in a range of −52 to −87 ppm/K, and the absolute values of dn TE /dT are significantly larger than those for dn TM /dT for all PI films. As predicted from the temperature derivative of the Lorenz-Lorenz equation, the amorphous PI films with high n av exhibit large |dn av /dT|. On the other hand, significant polarization dependences of dn/dT, which are observed as the temperature gradients of birefringence (d(∆n)/dT), was observed even for the PI films having very small ∆n, although a large ∆n should cause a large d(∆n)/dT according to the temperature derivative of the Vuks equation. The significant d(∆n)/dT observed for the PI films with small ∆n is originated from the large residual stress (~50 MPa) induced on the films derived from the mismatch in thermal expansion between the PI and Si substrate. Since residual stress on the films decreases as temperature increases, the stress birefringence should exhibit temperature dependence, which causes significant polarization dependence in dn/dT.

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