pH-Responsive Capsules Fabricated by Interfacial Photo-Cross-Linking Utilizing the Photoreactivity and pH-Responsiveness of Thymine

Abstract

pH-responsive capsules are useful materials for various applications, such as drug delivery systems and nano-/microreactors. Herein, we developed pH-responsive capsules through interfacial photo-cross-linking with thymine-functionalized parent polymer particles, where thymine functioned as a photoreactive and pH-responsive group. A sufficient hydrophilicity of the capsule polymers was necessary to achieve the controlled release of encapsulated molecules by utilizing the pH-responsiveness of thymine groups. Based on a series of solubility tests for various polymers derived from 4vinylbenzyl thymine (VBT), styrene (St), 2-vinylpyridine (2VP), and 4-vinylpyridine (4VP), P(St-2VP-VBT) and P(St-VBT) were suitable for preparing capsule particles by interfacial photo-cross-linking. Release tests revealed that P(St-2VP-VBT), but not P(St-VBT), could release its cargo under basic conditions, where thymine transforms from the nonionic to anionic state. This behavior indicates that the increased hydrophilicity of the polymer shell layer obtained by copolymerization with 2VP is critical for cargo release induced by thymine deprotonation. Furthermore, P(St-2VP-VBT) also responded to acidic pH owing to protonation of the pyridine groups. Finally, we successfully created acidic and alkaline dual pH-responsive capsules via interfacial photo-cross-linking using P(St-2VP-VBT) particles.

Visible Light Induced Interfacial Photo-Cross-Linking for Fabrication of Polymer Capsules Using Photoreactive Polymers with Substituted Cinnamates

“…Interfacial photo-cross-linking of polymer particles has been developed as a facile preparation route for various functional capsule polymer particles. − In this approach, the [2 + 2] photodimerization reaction between photoreactive groups (e.g., cinnamate, coumarin, and thymine , ) is used as a cross-linking reaction between different polymer chains in particulate states. Furthermore, photoinduced cross-linking occurred only at the particle interfacial region owing to the photoabsorbance of the external light by the nonreacted cinnamate groups remaining in the polymer interfacial region.…”