Stimuli-responsive polymer architectures

Abstract

Light-responsive polymers systems, in both the dry state and hydrogel state were prepared to investigate nano-scale light-induced transitions. Pendant spiropyran (meth)acrylated block copolymers were fabricated via atom transfer radical polymerization (ATRP) and the nano-scale phase separation of thin films of spin coated films were investigated with tapping-mode atomic force microscopy (TM-AFM). Nano-scale phase separated films of spiropyran methacrylate copolymers were observed to exhibit changes in the phase separation profile when exposed to UV-light. The molecular weights, volume fraction, and phase separation were determined by NMR spectroscopy, GC and GPC, and AFM. Hansen solubility parameters were determined for mixed block copolymer poly(meth)acrylates by the group contribution method. Hydrogel systems that responded to UV-light stimulus were also prepared as switchable adhesives. The polyacrylamide hydrogel contains a biomimetic 3,4-dihydroxyphenethylamide (DOPA) linkage group sensitive to pH. When the hydrogel is doped with a photoacid generator, diphenyliodonium chloride, and exposed to UV-light, the acidification induces an in situ titration of the DOPA groups, degrading the gel network. The mechanism of network degradation was investigated by UV-vis spectroscopy, rheometry, and lap-shear adhesion studies. Irradiation of these hydrogels with UV light affords a viscous liquid solution, demonstrating a gel-sol transition with a subsequent decrease in the adhesive strength of the material. These gels may be prepared in high throughput and require few synthetic steps with commercially available precursors. These advantages of high throughput and biomimicry are important for preliminary investigations into biocompatibility of the gel, showing an antimicrobial zone of inhibition to Staphylococcus aureus when loaded with 5.1 mg•mL–1 neomycin sulfate.