Measurement of Hansen Solubility Parameters of Poly(ether ether ketone) Using Inverse Gas Chromatography

In this study, the Hansen solubility parameter (HSP) was determined by applying inverse gas chromatography (IGC) to poly(ether ether ketone) (PEEK), a poorly soluble resin. PEEK is a semicrystalline functional polymer that is difficult to dissolve in organic solvents at room temperature, making it impossible to determine the HSP through solubility tests. In the experiments, we identified conditions under which the Flory–Huggins interaction parameter between 11 solvents and the amorphous regions of PEEK could be determined using IGC. These values were used to achieve a reproducible HSP estimation. The HSP of the amorphous regions was also determined using a Hansen solubility sphere by measuring the swelling ratio of PEEK pellets after immersion in each solvent for 2 weeks. The HSPs obtained with the two methods agreed very well, confirming the HSP determined using IGC. Using IGC to evaluate affinity has advantages such as high reproducibility and high throughput, as well as significantly reduced contact between organic solvents and the experimenter compared with measuring the swelling ratio. Therefore, IGC is expected to enable simple and safe affinity determination for poorly soluble resins in the future.