Competition between CO₂-philicity and Mixing Entropy Leads to CO₂ Solubility Maximum in Polyether Polyols

Area of Science:

• Materials Science
• Polymer Chemistry
• Chemical Engineering

Background:

• Carbon dioxide (CO2) is increasingly used as a blowing agent in polyurethane foams, replacing environmentally harmful alternatives.
• The solubility of CO2 in polyols significantly influences the structure and properties of the resulting polymer foam.
• Previous research focused on CO2 solubility in low molecular weight polyols, leaving a gap in understanding for high molecular weight polyols used in commercial foams.

Purpose of the Study:

• To investigate the effect of molecular weight and functionality on CO2 solubility in high molecular weight polyether polyols.
• To understand the underlying mechanisms governing CO2 solubility in these polyols.
• To develop and validate a model for predicting CO2 solubility in polyether polyols.

Main Methods:

• Gravimetry and axisymmetric drop-shape analysis were employed to measure CO2 solubility.
• Perturbed chain-statistical associating fluid theory (PC-SAFT) was used to model CO2 solubility.
• Density functional theory was utilized to validate the PC-SAFT model by predicting interfacial tension.

Main Results:

• CO2 solubility in polyether polyols was found to decrease with increasing molecular weight above 1000 g/mol.
• Higher polyol functionality was correlated with decreased CO2 solubility.
• The nonmonotonic effect of molecular weight is attributed to competing entropic and end-group effects.

Conclusions:

• The study elucidates the critical role of molecular weight and functionality in dictating CO2 solubility in polyether polyols.
• The findings provide valuable insights for optimizing the formulation of CO2-blown polyurethane foams.
• The validated PC-SAFT model offers a predictive tool for CO2 solubility in polyols, aiding material design.