Entrainer Effect of N,N-Dimethylformamide on Solubility of Monomers for Aromatic Polyimide in Supercritical Carbon Dioxide

Abstract

The solubilities of 4,4′-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) in supercritical carbon dioxide (scCO2) with N,N-dimethylformamide (DMF) were measured by a semibatch flow method, to accumulate new experimental data and to clarify the entrainer effect of DMF on the solubilities of the monomers of aromatic polyimide in scCO2. All measurements were carried out at 323 K and 20.0 MPa with DMF concentrations from 0 to about 20 mol %. The solubilities of both ODA and PMDA increased dramatically with increasing DMF concentration under our experimental conditions. For example, the addition of about 10 mol % of DMF increased the solubilities of ODA and PMDA to 54- and 115-fold, respectively, as compared to their solubilities in pure scCO2. The experimental results were correlated and predicted by the Peng–Robinson equation of state (PR-EOS). The critical temperatures and pressures of ODA and PMDA were estimated utilizing the group contribution method proposed by Constantinou and Gani, and the solid molar volumes of ODA and PMDA needed for calculation were obtained by the COSMO-RS method. The vapor pressures of ODA and PMDA, which are also required to calculate the solubilities, were obtained by correlating the solubilities of ODA and PMDA in pure CO2. The binary interaction parameters were estimated by correlating the phase equilibria and solubilities for each binary system. The predicted results approximately reproduced the experimental results for the solubilities of ODA in scCO2. As for the solubilities of PMDA, while a large deviation was observed between the predicted and experimental results, the correlated results approximately corresponded to the experimental data.

Measurement and prediction of the solubilities of aromatic polyimide monomers in supercritical carbon dioxide with acetone

“…In the UV-Vis spectroscopy for API monomers, the absorbance peaks of the monomers were influenced by those of acetone. On the other hand, DMF did not interfere with the absorbance peaks of the monomers at the same wavelength in the previous work [5]. Therefore, as described previously, the acetone dissolving monomers were carefully vaporized at 313 K, and the monomer that remained in the flask was redissolved in DMF prior to the UV-Vis spectroscopy.…”

“…An apparatus based on the semi-batch flow method was developed in previous work [5], and was also used in this work. A schematic diagram of the experimental apparatus is shown in figure 2.…”

“…The calibration curves for both API monomers were prepared using DMF as in the previous work [5]. There were 2 main peaks in the absorbance spectra that ranged from (200 to 400) nm, at about 267 nm and 310 nm for ODA and at about 270 nm and 305 nm for PMDA.…”

“…The P sat S of ODA and PMDA, which are needed for the solubility calculations as described in equation (2), were cited in the literature [11]. On the other hand, the v S of the API monomers were measured using a glass pycnometer at room temperature and atmospheric pressure in the previous work [5]. The / F S of ODA and PMDA in the scCO 2 phase with acetone was obtained using the PR-EOS [8] and the following thermodynamic relationship:…”

“…In our previous work [5], the solubilities of 4,4 0 -diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA), which are representative compounds of an aromatic diamine and tetracarboxylic dianhydride monomers for API polymerization, in scCO 2 with and without an entrainer were measured to accumulate new experimental data for API production and to clarify the entrainer effects of the co-solvent. N,N-dimethylformamide (DMF), which is one of the most representative solvents for solution polymerization of API, was used as the entrainer.…”