Photo-crosslinked persistent micelle templates with near universal solvent compatibility

Abstract

The controlled preparation of porous nanomaterials from block polymer templates is important for diverse applications from energy devices to optical coatings and sorbents. The architectural dimensions determine the overall performance for many of these applications, however the independent control of these dimensions has remained limited to a narrow range of solvent conditions for kinetically trapped (“persistent”) micelle templates. Polymers with a photo-reactive chemistry are shown to enable cross-linked micelle templates that universally remain persistent under diverse solvent conditions. Specifically, poly(poly(ethylene glycol methacrylate))-b-poly(butyl methacrylate-co-coumarin methacrylate) (OBC) was prepared by RAFT polymerization and the resulting micelles were crosslinked with UV light (X-OBC). TEM images revealed that crosslinking in MeOH-only led to a mixture of micelles and unimers whereas crosslinking in MeOH–H₂O led to pure micelles. Absorbance measurements indicated 50% coumarin dimerization (crosslinking) occurred after 180 min of UV exposure. The near universal solvent compatibility of X-OBC persistent micelles is demonstrated with DLS measurements in toluene, DCM, DMF, THF, EtOH, and MeOH, whereas OBC is shown to release unimers in DCM, DMF, THF, and toluene, or precipitate from EtOH due to a morphology change. Spectroscopic testing of micelle crosslinking occurred at each templating step. Micelle entrapment was also validated with SAXS and SEM measurements after nanomaterial templating where X-OBC enabled sample series with constant pore size whereas OBC did not. Furthermore, the results uniquely show X-OBC micelle persistence when processed from non-selective solvents. These results highlight how molecular engineering and tailored processing can enable the generalized synthesis of controlled porous nanomaterials.