The Interplay between Solvent Loss and Thermal Cyclization in LARC-TPI

Abstract

Isothermal reaction kinetics are reported for the thermal cyclization of the poly (amide-acid) based on benzophenone tetra-carboxylic acid dianhydride reacted with 3,3'-diaminobenzophenone. Isothermal solvent loss kinetics are also reported. The data suggest a strong interdependence between the rate of imidation and the rate of solvent loss. Additional reactions may occur for isothermal reaction temperatures above about 180°C. Infrared analysis showed the presence of moisture even at elevated temperatures; hence, hydrolysis is one possible side reaction. Infrared spectra of films exposed to elevated temperatures further suggest that complete solvent removal is difficult. The infrared band assignments are proposed. The kinetic data were fitted to a modified absolute reaction rate theory equation where the time dependence of the reaction rate constant may be explained by entropic changes which follow a continuous function of time. The reaction kinetics yielded reasonable values for the frequency of vibration of the activated complex transition state and the activation energy. Low values for the activation entropy may be explained by solvent effects. The solvent loss kinetic model yields an estimate of the polymer-solvent interactions. 273K. L. Mittal (ed.), Polyimides

Fourier transform infrared spectroscopy of some miscible polybenzimidazole/polyimide blends

“…This pattern is characteristic of cyclic imides, 10 and it has been ascribed to symmetric and asymmetric imide carbonyl vibrations.11 Mixed-mode assignments, analogous to those seen in polyamides, have also been proposed. 12 The low absorbances of polyimides in the N-H stretching region of PBI, and of PBI in the carbonyl region of the Pis, means that a computer subtraction of the pure polymer spectra from that of the blends was not needed in this study to define the locations or shapes of these bands. Figure 2 shows the IR spectra of PBI and of some representative blends of PBI with XU 218 in the 3500-3000 cm-1 region.…”

Polyimide−Ceramic Hybrid Composites by the Sol−Gel Route

“…PIs are generally insoluble in organic solvents and are therefore fabricated into products such as films and coatings using a soluble PI precursor, typically polyamic acid (PAA). 13,14 A typical preparation involves mixing solutions of a dianhydride (e.g., pyromellitic anhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), or 2,2-bis(3,4-dicarboxy-phenyl)-hexafluoropropane dianhydride (6FDA)] with a diamine [e.g., 4,4′oxydianiline (ODA)] in a convenient solvent [e.g., dimethylacetamide (DMAC) or N-methyl pyrollidone (NMP)]. A metal oxide precursor [e.g., tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS)] is then added and the hydrolysis and polycondensation are carried out, using an appropriate catalyst.…”

Hydrogen bonding in poly(amic acid)s

“…Infrared spectroscopic studies of polyimide films can be roughly divided into two categories. In the first, ring closure is implicitly assumed and various bands used as a measure of the degree of imidization.1"5 The second category involves the use of infrared spectroscopy as a tool for identifying the species actually formed (for example, see ref [6][7][8][9][10][11]. In this context, a distinction between the products obtained by chemical as opposed to thermal curing can also be made.…”