Photocrosslinked and pH-switchable Soft Polymer Nanocapsules from Polyglycidyl Ethers

Soft polymer nanocapsules and microgels, which can adapt their shape and at the same time sequester and release molecular payloads in response to an external trigger, are a challenging complement to vesicular structures like polymersomes. In this work we report the synthesis of such capsules by photocrosslinking of coumarin-substituted polyglycidyl ethers, which we prepared by Williamson etherification of epichlorohydrin (ECH) repeating units with 7-hydroxycoumarin in copolymers with tert-butyl glycidyl ether (tBGE). To control capsule size, we employed the prepolymers in an o/w miniemulsion, where they formed a gel layer at the interface upon irradiation at 365 nm by [2π+2π] photodimerization of the coumarin groups. Upon irradiation at 245 nm, the reaction could be reversed and the gel wall could be repeatedly disintegrated and rebuilt. We further demonstrated (i) reversible hydrophilization of the gels by hydrolysis of the lactone rings in coumarin dimers as a mechanism to manipulate the permeability of the capsules, and (ii) binding functional molecules as amides. Together with the possibility to hydrolyze the tert-butyl ether group we demonstrate a remarkable versatility of such nanogels for their use as a carrier system.