Structure, Properties, and Intermolecular Charge Transfer of Polyimides

Abstract

The presence of intermolecular donor-acceptor interaction in solid state aromatic polyimides (PIs) was confirmed by spectroscopic means. It was found that the thermal expansion coefficient is closely associated not only with the degree of in-plane orientation, but also with the degree of molecular stacking. These two factors influence each other, and are not completely independent. The intermolecular CT fluorescence spectra were a sensitive reflection of the molecular stacking process. Dynamic mechanical measurements of PIs suggested that the CT complexes probably function as physical crosslinks.Aromatic polyimides (Pis), especially those possessing a rigid (linear) polymer backbone, e.g., PI(BPDA/PDA) (BPDA: 3,4,3\4 f ,-biphenyltetracarboxylic dianhydride, PDA: /?-phenylenediamine), show properties depending strongly on the cure method (chemical and thermal), thermal imidization conditions (final cure temperature and heating rate), presence of substrate, and film thickness. This is attributed to the difference of the degree of molecular orientation and molecular stacking which are closely related with molecular mobility during thermal cure of polyamic acid (PAA). The aim of the work is to elucidate the presence and contribution of intermolecular charge-transfer (CT) interaction on various physical properties and to examine the relationship between physical properties and the structures of molecular aggregates. The intermolecular charge-transfer (CT) fluorescence is useful as an indicator of the degree of PI chain packing(I-i) and the miscibility of PI/PI binary blends. (4) Recently, Okabe et al. (5) reported that a PI derived from a polyamic acid ester (PAE) has a thermal expansion coefficient (TEC) higher than the PI made from the corresponding PAA. The present paper also describes the difference of molecular aggregation structure between Pis from PAA and PAE, characterized by the intrinsic intermolecular CT fluorescence(!,3) and the dichroic absorption spectra measured at a tilt angle for a rigid-rod dye dispersed in PI film. (6) EXPERIMENTAL SECTION Materials. PAAs were polymerized by adding equimolar amounts of dianhydride powder into a iV,N-dimethylacetamide (DMAc) solution of diamine at room

Synthesis and properties of polyimides-containing benzoxazole units in the main chain

“…Compared with PI-a annealed at 400°C, the 350°C counterpart possessed lower tensile modulus and strength. As annealing at higher temperatures tend to promote intermolecular association between the macromolecular chains, especially for those rigid-rod polymer backbones, 15,25,26 the improvement in mechanical property of PI-a annealed at 400°C demonstrated the positive role that stronger intermolecular interactions played to enhance the properties of PI films. PI-e, based on BPADA, had the lowest tensile modulus and strength; this could be attributed to the flexibility of chain arising from the ether linkage and isopropyl group in the dianhydride moiety.…”

Differences in thermo-mechanical properties and intermolecular charge-transfer characteristics of the aromatic polyimide PI(BPDA/PDA) from various precursors

“…1 are different from each other and the order of density is arranged as follows: PAA (1.4555 g/cm 3 ) A PAAE (1.4480 g/cm 3 ) A PABE (1.4463 g/cm 3 ). This seems to imply that the density of PI(BPDA/PDA) from polyamide esters is smaller than that from PAA, which would be due to the difference in molecular mobility during thermal cure of various precursors, caused by the differences in hydrogen-bonding ability with the solvent, imidization rate, and/or the size of the volatile group outgassed during imidization 21) .…”

Synthesis and properties of polyimides containing hexaisobutyl-substituted T8 cages in their main chains

“…[1][2][3] Polyimide lms, however, usually show yellow or brown color due to absorption characteristics in the visible region, caused by intra-and intermolecular charge transfer (CT) interactions of the polymer backbones. [4][5][6][7] The CT interactions occur between electron-rich nitrogen atoms and electron-poor carbonyl groups, which are characteristic of the imide group. To resolve this color problem, alicyclic or uorinated polyimides are usually employed to diminish the CT interaction.…”