Relationship between Molecular Aggregation Structures and Optical Properties of Polyimide Films Analyzed by Synchrotron Wide-Angle X-ray Diffraction, Infrared Absorption, and UV/Visible Absorption Spectroscopy at Very High Pressure

Abstract

The relationship between the molecular aggregation structures and the optical properties of fully aromatic and semialiphatic polyimide (PI) films were analyzed by synchrotron wide-angle X-ray diffraction (WAXD), infrared absorption, and UV/visible absorption spectroscopy at very high pressures up to 8 GPa. The PIs showed significant reduction in the interchain distances in the first stage of compression up to 1 GPa, which resulted in an appreciable decrease in the interchain free volume. In addition, reduction in the C−C bond lengths of aromatic rings by ca. 0.7% was confirmed by the pressure-induced high wavenumber shift of the infrared stretching vibration of the PIs. Furthermore, pressure-induced bathochromic shifts were observed in the locally excited (LE) absorption band of PIs, which are related to the enhanced van der Waals interaction caused by the reduced interchain distances. The intensity of the charge transfer (CT) absorption band of s-BPDA/PDA poly(p-phenylene biphenyltetracarboximide) PI was reduced up to 0.3 GPa, indicating that conformational changes affect the intramolecular CT interactions. In contrast, the CT absorptions of PMDA/ODA (poly(4,4′-oxidiphenylene pyromelliticimide) and PMDA/DCHM (poly(4,4′-diaminocyclohexylmethane pyromelliticimide) PIs were enhanced by increasing the pressure, which was caused by an enhancement of intermolecular CT interactions. The significant variations observed in the LE and intermolecular CT bands below 1 GPa accord with the significant decrease in the interchain distance, as indicated by synchrotron WAXD.

Measuring structural inhomogeneity of a helical conjugated polymer at high pressure and temperature

“…These studies were augmented by structural high pressure studies of polyphenylenes by Heimel et al and Gitsas et al, and by optical high pressure studies including studies of poly( p‐ phenylene vinylene) by Morandi et al and investigations of fluorene copolymers by Schmidtke et al Common to all these studies are planarization of otherwise twisted polymers followed by a redshift in photoluminescence (PL). Also, there are structural high pressure studies of oligoacenes and related molecules including fluorene as well as of related hairy rod type polymers like polyimides, which show diverse structural transitions and dependencies between the effect of pressure and side chain structure.…”

Effect of fluorination on haze reduction in transparent polyimide films for flexible substrates

“…Interestingly, the increase in the degree of fluorination in FPI diminished the interaction energy between the layers in the order of 1FPI (−1.43 eV) > 2FPI (−0.76 eV) > 3FPI (−0.52 eV) > 4FPI (−0.43 eV) because the fluorinated groups separated the FPI chains, placing them in a free space with the interactive orientation. Notably, fluorinated groups in dianhydrides reduce the related chain entanglements because of the milder intra‐ and intermolecular interactions between the dianhydride and diamine groups, ultimately inhibiting haze formation (Table ) …”

Preparation and characterization of inherently heat‐sealable polyimides with high glass transition temperatures

“…The rigid and regular chemical structure renders PDA much difficult as the monomer for the preparation of soluble polyimide. Consequently, PDA‐derived PI film is generally fabricated via two‐step method including synthesis of polyamide acid (PAA) and subsequent heat imidization . Favorably, in our research, all these CPIs exhibit good solubility in the polar aprotic solvents, NMP, DMAc, DMF, and m ‐cresol, as shown in Table .…”