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

Abstract

The differences in thermo-mechanical properties and intermolecular charge-transfer (CT) characteristics of an aromatic polyimide, PI(BPDA/PDA), from polyamide acid (PAA), polyamide allyl ester (PAAE), or polyamide benzyl ester (PABE) precursors were studied. The various PI(BPDA/PDA)'s show identical uniformity in chemical structure and thermogravimetric behavior. PI(BPDA/PDA) from PAA however shows higher density and T g and lower thermal expansion coefficient than those from PAAE and PABE, indicating the higher orderliness of the molecular packing of PI(BPDA/PDA) from PAA. Intermolecular ground-state CT complexes of PI(BPDA/PDA) from PAAE and PABE show fluorescence at longer wavelengths and wider fluorescence peak wavelength range than the one of PI(BPDA/PDA) from PAA. This suggests the wider variety of aggregation structures of PI(BPDA/PDA) from PAAE and PAGE than those of PI(BPDA/PDA) from PAA. The steric hindrance of the bulky substituents of PAAE and PABE would cause an increase in the variety of aggregation structures during imidization. The shorter fluorescence lifetimes of PI(BPDA/PDA) from PAAE and PABE than the one of PI(BPDA/PDA) from PAA also confirm the differences in their intermolecular CT characteristics.

A study on the effect of spirocyclic structures in the main chain on the physical properties of copolyimides

“…It was assumed that the degree of imidization was 100% for the sample heated at 350 8C for 15 min after heating at 240 8C for 2 h. The degree of imidization for the thermally imidized samples was estimated by comparing the absorbance ratio of the 1 776 cm -1 band (m C=O in imide ring) to the 1 515 cm -1 band (m C=C in benzene ring) with that of the above exhaustively imidized samples. [25] With increasing DAn units, the degree of the imidization tends to decrease. Flexible films were obtained for either thermally or chemically imidized coPIs, provided that the DAn content exceeds a certain value.…”