Covalent Stabilization of Inverse Bicontinuous Cubic Structures of Block Copolymer Bilayers by Photodimerization of Indene Pendant Groups of Polystyrene Hydrophobic Blocks

We report the cross-linking of hydrophobic compartments of complex self-assembled structures of amphiphilic block copolymers (BCPs) by the [2π + 2π]-cycloaddition of indene moieties present in a hydrophobic block based on polystyrene (PS). A photodimerizable indene group was introduced to the PS block by controlled radical copolymerization of indanolyl­styrene, which was subsequently dehydrated to indenyl­styrene using the Burgess reagent. This mild conversion producing the photodimerizable indene pendant groups ensured the synthesis of BCPs with a photo-cross-linkable PS block. We demonstrate that the micellar structures and complex inverse bicontinuous bilayers of BCPs containing hydrophobic PS cores could be covalently cross-linked in aqueous solutions upon irradiation with long-wavelength UV light (λ = 365 nm). The procedure formed an infinite polymer network within the hydrophobic compartments of the self-assembled nanostructures without using any additional reagents or causing morphological changes during the cross-linking. A wide variety of self-assembled structures retained their structural integrity in common organic solvents after cross-linking of the hydrophobic PS blocks.