Photo-cross-linkable polymer micelles in hydrogen-bonding-built layer-by-layer films

Photoactive micelles of a diblock copolymer composed of poly(ethylene oxide) and poly(7-(2-methacryloyloxyethoxy)-4-methylcoumarin) (PEO-b-PCMA) were layer-by-layer assembled with poly(acrylic acid) (PAA) using hydrogen-bonding between the PEO corona of the micelles and the PAA chains (pH < 3). In addition to characterizing the assembly process using a number of techniques, the tunable photo-cross-linking of polymer micelles through dimerization of the coumarin groups was used to generate interesting functions for the multilayer film. On the one hand, the easy tuning of the photo-cross-linking density could be used to control the release rate of hydrophobic guest molecules loaded in the film. On the other hand, after chemical cross-linking of PAA to stabilize the film, the photo-cross-linking of the micelles could be used to restrict the dissolution of PEO-b-PCMA chains in a good organic solvent; this cross-linking-dependent extraction of polymer micelles was utilized to vary the porosity of the film.