High Temperature Polyimide Synthesis in ‘Active’ Medium: Reactivity Leveling of the High and the Low Basic Diamines

Abstract

The kinetics associated with the reaction of aromatic and aliphatic diamines with phthalic anhydride in glacial acetic acid was studied. This model system was intended to simulate the synthesis of polyimides from diamines and dianhydrides in molten benzoic acid. The reaction proceeds in two discrete steps, the first acylation occurs by the reaction of the diamine with phthalic anhydride followed by cy-clodehydration of the corresponding bis-(o-carboxyamides). The focus of the work was on the influence of chemical composition and basicity of the diamines on the kinetics. Kinetic and thermodynamic characteristics of model reactions were determined. It was established that acylation of aromatic and aliphatic diamines in acid medium proceeds as a reversible second-order reaction catalyzed by acid medium. On the basis of kinetic data obtained, an explanation is given for the observed phenomenon of reactivity leveling of diamines regardless of the basicity.

Formation of the chain microstructure in copolyimide synthesis by high-temperature polycondensation in molten benzoic acid

“…The reaction was carried out in a temperature controlled cell of an APT 09 Akvilon automated potentiometer using an earlier described procedure. 25 A solution of PA in AcOH was added to a solution of DDA or AFL in AcOH (both solutions were kept at a constant temperature). The initial concentrations of the re actants were с AFL = 0.03 mol L -1 , с PA = 0.031 mol L -1 and с DDA = 0.01 mol L -1 , с PA = 0.011 mol L -1 .…”

Synthesis of Polyimides in the Melt of Benzoic Acid

“…In the course of experiments with different monomer pairs ( Table 1), it was found that the chain growth rate in molten BA showed a rather weak dependence on the basicity of the diamines used [13,15,16]. This observation is in stark contrast to regularities of the low-temperature polycondensation in amic solvents in which the basicity of the diamines has a strong influence on the rate of polycondensation [1][2][3].…”

“…Kinetic data were obtained by potentiometric titration of amino groups with solution of perchloric acid in AcOH after reaching an equilibrium state [16,17]. Results are presented in Table 3 [16,17].…”

“…In Table 4, the values of rate constants at 140°C obtained by extrapolation are given. (4) with phthalic anhydride [16,17].…”

Achievements in polycondensation and condensation polymers

“…Kuznetsov et al showed that the synthesis of PIs, including branched PIs, efficiently occurs in the molten benzoic acid, which serves as an active medium during the formation of these types of poly mers [55][56][57][58][59].…”