Pressure-Induced Changes in Crystalline Structures of Polyimides Analyzed by Wide-Angle X-ray Diffraction at High Pressures

Abstract

Variations in the crystalline structures of polyimides (PIs) were analyzed under high pressures up to 8 GPa using wide-angle X-ray diffraction. The compressibilities along the polymer chain axis (c-axis) of rigid-rod PIs increased with an increase in the number of phenyl rings in the diamine moiety (PMDA/PPD < PMDA/BZ < PMDA/DATP). This could be due to an increased shrinkage of the C−C bond lengths between the phenyl rings and/or a pressure-induced deformation of the periodic structure associated with changes in bond angles and dihedral angles. In contrast, PMDA/ODA, having an ether linkage, showed an increase in the lattice parameter along the c-axis up to 0.8 GPa, which could be due to a widening of the ether bond angle. Moreover, PMDA/PPD showed isotropic compression along interchain directions, whereas PMDA/DATP and PMDA/ODA showed anisotropic compression along the cofacial stacking direction, which resulted in the larger volumetric shrinkages of the latter PIs.

Nitrogen‐Doped Porous Carbon Superstructures Derived from Hierarchical Assembly of Polyimide Nanosheets

“…The chemical composition and crystalline structure of the resulting PIs were confi rmed through Fourier transform infrared spectroscopy (FTIR) spectroscopy (Figure S1a, Supporting Information) and X-ray powder diffraction (XRD) ( Figure S1b, Supporting Information). [ 25,26 ] Scanning electron microscopy (SEM) images showed that the samples prepared using DMF or NMP clearly exhibited different 3D hierarchical architectures, although they were constructed by 2D nanosheets ( Figure 2 ). Among them, the In the last decade, 3D carbon superstructures (CSSs) constructed from the assembly of low-dimensional segments such as carbon nanotubes or graphene sheets, have attracted increasing interest.…”

“…Based on these results, we propose a pressure-induced, concentration-dependent hierarchical self-assembly mechanism for explaining the formation of PI nanosheets and their assembly into 3D superstructures: Under solvothermal reaction conditions, a high temperature facilitates the dehydration of polyamic acid, and high pressure induces the crystallization of the resultant PI. [ 26,29 ] As shown in Figure 1 , the folding of a 1D linear PI chain with strong intermolecular forces fi rst induced the formation of fl at nanosheets, which further organized into 3D assemblies with various morphologies depending on the polyamic acid concentration. The hierarchical self-assembly mechanism of PI is highly similar to the growth of the lamellar structures and spherulites of polymers ( Figure S4, Supporting Information), [18][19][20][21] in which the diluted solution of polyamic acid tends to form lamellar structures through molecular chains orienting perpendicularly to the nanosheet surface.…”

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.…”

Anisotropic Linear and Volumetric Thermal‐Expansion Behaviors of Self‐Standing Polyimide Films Analyzed by Thermomechanical Analysis (TMA) and Optical Interferometry

“…For the PMDA–PIs, it should be noted that PMDA–DCHM, which possesses two cyclohexyl rings with a bent CH 2  linkage, exhibited a large K p (0.635) compared with the PIs with linear structures (0.603–0.613). This should have resulted from the ordered structures in PMDA–DCHM, which was characterized by wide‐angle X‐ray diffraction in our previous study . A sharp peak for d = 16.1 Å (002) and a broad peak for d = 5.1 Å (chain packing) were observed for this PI.…”