Thiol–Ene Interfacial Photo-Cross-Linking for Ultrathin Rubbery Polymer and Nanoparticle Films as Membrane Selective Layers

Thin-film composite (TFC) membranes fabricated by interfacial polymerization (IPz) underpin modern separations, yet their chemistry remains dominated by polyamide systems. Here, we introduce a versatile thiol–ene interfacial photo-cross-linking strategy as an expansion of IPz to produce ultrathin films as membrane selective layers. In particular, vinyl-rich polymers or vinyl-functionalized nanoparticles were cross-linked with dithiols at a water/oil interface under UV irradiation in ambient air. We first show that this process can be effective for three vinyl-containing systems─poly(dimethylsiloxane) (PDMS) as poly(dimethyl-co-vinylmethyl siloxane), poly(1,2-butadiene) (PB), and vinyl-functionalized silica nanoparticles (SiNPs)─with the three systems readily forming nonporous (PDMS, PB) and porous (SiNPs) thin films. We further explored the two polymeric systems, including the impact of reaction time, dithiol type, and reactant ratio on film thickness and properties. PDMS-derived layers exhibited dense morphologies and near-zero water permeability, but with relatively thick films of 1–7 μm. Under similar reaction conditions, PB-derived films had much lower thicknesses of 60–200 nm and had minimal defects, as demonstrated by phenol/NaCl selectivities as high as 2000 under optimized thiol:ene ratios and reaction times. Infrared spectroscopy and electron microscopy supported efficient thiol–ene addition and continuous coverage of the porous support. We attribute the greater thicknesses in PDMS to greater expected permeabilities of reactants through the nascent film. This work extends thiol–ene IPz as a robust, oxygen-tolerant, and scalable platform for fabricating ultrathin selective layers, and can serve as a foundation for future work to form chemically modifiable nonporous and porous nanofilms.