Low-cost and scalable type II/III porous liquids from surface-engineered hypercrosslinked polymers with enhanced molecular separation performance

Porous liquids (PLs) combine permanent porosity with liquid-like processability, presenting a promising pathway for scalable molecular separations; yet, their practical application is often limited by cost and long-term instability. This study presents a low-cost route to stable Type II/III PLs by integrating cost-effective Friedel-Crafts-derived hypercrosslinked polymers (HCPs) with sterically hindered, branched PEG-based solvents (trimethylolpropane ethoxylates; M n = 170 and 450 g.mol −1 , referred to as 3AP LM and 3AP HM ). HCPs were synthesised from eight monomers at the monomer:FeCl 3 :FDA ratios of 1:1:1 and 1:2:1 to tune porosity and surface functionality. Increasing FeCl 3 loading enhanced crosslinking and significantly increased surface area, while generally decreasing the availability of surface -OH groups. This indicates a porosity-functionality trade-off relevant for required modification. To enable stable dispersions/dissolutions in PEG media, selected HCPs were interfacially modified using a simple two-step corona-canopy approach (DTAC organosilane grafting followed by PEG-sulfonate functionalisation), which resulted in ether/sulfonate-rich interfaces that enhance solvent compatibility. Twenty-two HCP-solvent combinations were first screened at 1 wt% by observing sedimentation and Tyndall effects as well as accessible surface area via CO 2 sorption, and subsequently prioritised using a stability index to find potential candidates. Selected formulations were then prepared at 10 wt% and validated as practical PLs: viscosities ranged from 0.6 to 156.7 Pa.s (298 K), with several close to the neat solvents (e.g., Ph 121-Mod -3AP LM : 3.7 Pa·s vs 3AP LM : 3.5 Pa·s). Measured densities were consistently below ideal-mixture predictions (e.g., BA 111-Mod -3AP HM : 1.0999 vs 1.1032 g.cm −3 ), consistent with retention of free volume and steric exclusion. PALS results were consistent with persistence of host-associated microporous free volume in the liquid formulations (lifetimes (τ 3 ) = 2.5–2.6 ns; ~0.6–0.7 nm effective cavity sizes), while Intensities (I 3 ) decreased relative to the neat solvents, indicating an altered liquid microenvironment upon addition of the porous phase. In a proof-of-concept for molecular separations, 10 wt% PLs improved the extraction of Sudan I from dodecane, achieving 63.6% with 3AP LM -based PLs and 68.7% with 3AP HM -based PLs. This study offers a cost-effective, scalable method for producing stable HCP-based Type II/III PLs with confirmed permanent porosity and proven molecular separation efficacy.