Hydrogen-Bonding Interactions in Polymer–Organic Solvent Mixtures

• Published in: Macromolecules 2022-06, Vol.55 (11), p.4578-4588
• Main Authors: Du, Ming-Xuan, Yuan, Ya-Fei, Zhang, Jin-Ming, Liu, Chen-Yang
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.2c00799

Polymer solubility in organic solvents generally is predicted by the Hildebrand solubility parameter (δ) approach based on the “like dissolves like” principle. A conspicuous exception is that there exist many soluble pairs that the solubility parameter approach predicts to be insoluble due to the large δ difference between the pair. These cases were attributed to specific attractive interactions (e.g., hydrogen bonding) between the solute and solvent that lead to a negative enthalpy of mixing to promote the solubility. Recently, we find that the polymer solubility in ionic liquids is dominated by hydrogen-bonding interactions (Phys. Chem. Chem. Phys. 2021, 23, 21893–21900). More importantly, three principles based on the Kamlet–Abraham–Taft multiple-polarity scale for dealing with hydrogen-bonding interactions were proposed. Two parameters (α is the hydrogen-bond acidity parameter, and β is the basicity parameter) are required to describe hydrogen-bonding complementarity. The product of ΔαΔβ, where Δ is the difference in parameters between the polymer and solvent, is an indicator of the competition between cross-association and self-association hydrogen bonding. Therefore, an excess interaction parameter χHB, which is proportional to ΔαΔβ, can be introduced to account for the solubility promotion. In this study, these principles were used to test the solubility of polymer/organic solvent mixtures, for which the solubility parameter approach fails. These polymer/organic solvent pairs that consist of 12 polymers and 27 organic small molecules have discrepant solubility parameters (>5 MPa1/2 at least). A good correlation between the solubility data and the solubility criterion (ΔαΔβ < 0) reveals that hydrogen-bonding interactions are responsible for the solubility. Therefore, the excess interaction parameter, χHB (∼ΔαΔβ), provides a significant correction in the Flory–Huggins theory. This finding can also serve as a prescreening tool for the solubility of polar polymers besides the “like dissolves like” principle.