Multifunctional thiols as additives in UV-cured PEG-diacrylate membranes for CO2 separation

The utility of incorporating only 20 mol% of multifunctional thiols into UV-cured poly(ethyleneglycol)diacrylate (PEGDA) membranes for CO2 separation is presented. Five different multifunctional thiols were investigated, spanning a range of functionalities from 2 to 4 and also different rigidities. All thiol-modified networks exhibited lower modulus values according to both small-strain and large-strain mechanical testing. This decrease in modulus was primarily attributed to a decrease in crosslink density via the step-growth thiol–acrylate reaction. Decreased crosslink density was more pronounced for dithiol additives which formed a “train-like” topology of connected PEGDA segments. Because of this more linear topology, dithiol-modified networks exhibited increases in gas permeability and strain at break. CO2 selectivity of each thiol-modified network was nearly comparable to the unmodified PEGDA network. Each network rapidly reached 100% conversion under a nitrogen atmosphere. However in air, the pure acrylate network reached negligible conversion while the networks modified with tri and tetrathiols reached noticeably higher conversions. Outdoor sunlight curing revealed that all thiol-modified networks were tack-free after only several minutes depending on thiol functionality. In contrast, the pure acrylate membrane remained tacky and uncured on the surface indefinitely. This study emphasizes the importance of thiol monomer selection in diminishing oxygen inhibition in UV-initiated acrylate polymerization as well as marked improvement in permeability for this specific PEGDA network via the incorporation of dithiols.

Research highlights▶ Incorporation of 20 mol% thiols into PEGDA membranes improved performance overall. ▶ All thiol-modified PEGDA networks showed comparable Tg and high CO2 selectivity. ▶ Permeability increased while maintaining high selectivity with addition of dithiols. ▶ Dithiols increased tensile strain at break due to decreased crosslink density. ▶ All thiols enabled outdoor sunlight curing of PEGDA membranes in 30 min or less.