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 Tg 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.