Preparation of stimuli-responsive hydrogel networks with threaded β-cyclodextrin end-capped chains via combination of controlled radical polymerization and click chemistry

Hydrogel networks of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-b-PPG-b-PEG primary network), with threaded sliding beta-cyclodextrin-capped poly(2-( methacryloyloxy) ethyl succinate) (beta CD-capped-PMES) chains, are described. The hydrogels were prepared by UV-initiated thiol-ene click reaction of the PEG-b-PPG-b-PEG diacrylate polymer with a crosslink agent, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), in the presence of beta CD end-capped chains, beta CD-capped-PMES. The latter was prepared a priori by reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the controlled character of RAFT polymerization and the quantitative yield of thiol-ene click reaction, the as-synthesized PEG-b-PPG-b-PEG-thread-beta CD-capped-PMES hydrogels have a well-defined PEG-b-PPG-b-PEG network and tunable PMES chain length. The length of PMES chains can be regulated by varying the molar ratio of 2-(methacryloyloxy) ethyl succinate (MES) monomer to RAFT agent. The molecular structures and thermal properties of the PEG-b-PPG-b-PEG-thread-beta CD-capped-PMES hydrogels were studied by H-1 NMR, XPS, TGA and DSC measurements. The polymer hydrogels with threaded sliding rings exhibit both pH- and temperature-dependent equilibrium swelling ratios in aqueous media and have potential applications as biomaterials and biomedical materials.