Temporally Controlled Curing of Block Polymers in the Disordered State Using Thermally Stable Photoacid Generators for the Preparation of Nanoporous Membranes

A lamellar forming poly(styrene-stat-glycidyl methacrylate)-block-polylactide, P(S-s-GMA)-b-PLA, diblock polymer containing the photoacid generator 4-iodophenyldiphenylsulfonium triflate (IST) was heated above its order–disorder transition temperature, TODT, and subsequently irradiated with UV light to kinetically trap the disordered state by acid-catalyzed cross-linking through the reactive GMA units. We demonstrated that IST remained thermally stable over relevant cross-linking temperatures and times allowing for the independent control over both the thermally induced disordering process and the onset of cross-linking, in contrast to related thermal cross-linking agents. Post removal of the PLA component, the photocured samples displayed a high degree of nanoporosity across a broad cross-linking temperature range that extends to at least 75 °C above the TODT. In-situ photocuring during small-angle X-ray scattering revealed that the cross-linking reaction had a minimal effect on the domain structure. Finally, we demonstrated that highly selective ultrafiltration membranes could be fabricated by spin-coating a P(S-s-GMA)-b-PLA diblock polymer containing IST onto a commercial polysulfone support, irradiating with UV light in the disordered state, and removing the sacrificial PLA domains.