Photocrosslinked poly(vinylbenzophenone)-core micelles via mild Friedel-Crafts benzoylation of polystyrene amphiphiles

Photocrosslinkable poly(vinylbenzophenone)-containing polymers were synthesized via a one-step, Friedel-Crafts benzoylation of polystyrene- containing starting materials [including polystyrene, polystyrene-block- poly(tert-butyl acrylate), poly-styrene-block-poly(ethylene oxide), polystyrene-block-poly(methyl methacrylate), and polystyrene-block-poly(n-butyl acrylate)] with benzoyl trifluoromethanesulfonate as a benzoylation reagent. The use of this mild reagent (which required no added Lewis acid) permitted polymers with well-defined compositions and narrow molecular weight distributions to be synthesized. Micelles formed from one of these benzoylated polymers, [polystyrene _0.25-co-poly(vinylbenzophenone) _0.75] ₁₁₅-block-poly(acrylic acid) ₁₄, were then fixed by the irradiation of the micelle cores with UV light. As the irradiation time was increased, the pendent benzophenone groups crosslinked with other chains in the glassy micelle cores. Dynamic light scattering, spectrofluorimetry, and Fourier transform infrared spectroscopy were all used to verify the progress of the crosslinking reaction.