In Situ IR Spectroscopy and Ab Initio Calculations To Study Polymer Swelling by Supercritical CO₂

Abstract

The CO(2) sorption and polymer swelling of hydroxytelechelic polybutadiene (HTPB) and poly(ethylene glycol) (PEG) have been investigated as a function of temperature and CO(2) pressure by combining in situ near-infrared spectroscopy with molecular modeling. The results reported here for the PEG-CO(2) system are in a very good agreement with literature data hence validating our experimental procedure. It has been found that CO(2) sorption and swelling effect is more important for PEG than for HTPB. For both polymers, an increase of temperature leads to a strong decrease of both the CO(2) sorption and swelling. In order to identify at a molecular level the nature and strength of intermolecular interaction occurring between CO(2) and the polymers, ab initio calculations have been performed on model structures, representative of the main functional group of the polymer, and their complex with CO(2). Trans-3-hexene (3-Hex), propyl methyl ether (PME) and methoxytrimethylsilane (MTMS) have been selected to mimic the functional groups of HTPB, PEG and polydimethyl siloxane (PDMS), respectively. The last system has been chosen since previous works on the swelling of PDMS by high pressure CO(2) have revealed the high ability of CO(2) to swell both uncrosslinked and crosslinked PDMS. The calculated stabilization energies of the MTMS-CO(2), PME-CO(2), and 3-Hex-CO(2) dimers indicate that CO(2) interacts specifically with the three moieties through a Lewis acid-Lewis base type of interaction with the energies displaying the following order: E(MTMS-CO(2)) = -3.59 > E(PME-CO(2)) = -3.43 > E(3-Hex-CO(2)) = -2.5 kcal/mol. Since the solubility of CO(2) in the corresponding homopolymers follows the same order, it is evidenced that the stronger the interaction between CO(2) and the polymer, the higher the CO(2) sorption. Therefore, even if one cannot exclude the influence of free volume and chain flexibility of the polymer, it appears that the solubility of CO(2) in the polymer is predominantly governed by the interaction between CO(2) and the polymer. Although the same trend is observed for the swelling of the polymer as a function of the CO(2) pressure, we have found that for a given value of CO(2) sorption, the swelling of the polymer depends on its nature, meaning that the swelling is not only governed by the CO(2)-polymer interaction but also by other intrinsic properties of the polymer.

Polymer nano-foams for insulating applications prepared from CO2 foaming

“…Vitoux and colleagues [38] highlighted the sorption temperature influence of the CO 2 uptake of poly(ethylene…”

In situ investigation of supercritical CO2 assisted impregnation of drugs into a polymer by high pressure FTIR micro-spectroscopy

“…In FTIR transmission measurements, the pathlength corresponds to the length of the cell hence it is fixed along the experiment 22,29 . On the contrary, the pathlength can change during the impregnation process in the developed set-up thanks to the use of the spring (figure 2).…”

“…Indeed, FTIR spectroscopy is more suited to analyze liquid and/or large samples (cm 3 ). 22,23 Besides, ATR-IR spectroscopy requires a good contact between the polymer and the crystal that is why the polymeric samples are generally melted to create a film on the crystal. 19 Consequently, the melting step impacts the polymer structure and so its behavior under scCO 2 .…”

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

“…This method has been previously successfully applied in phase equilibrium studies for the determination of the CO 2 sorption and swelling in liquids [18,19] and in polymers [20,21]. In particular, we would like to stress that molar absorption coefficients of CHstretching vibrational modes and combination bands are expected to exhibit little sensitivity upon temperature and pressure conditions [20,22,23].…”