Poly(disulfide)rotaxane slide-ring hydrogels with recoverable stretchability

Polyrotaxanes (PR) are structures based on the threading of macrocycles on an axis with end-stoppers; in pseudoPR (PPR), cycles can slide in and out of the axis. In our recent publication, macrocyclic thiolated-cyclodextrins (SHCD) were threaded onto PEG through host-guest interactions to fabricate thiol-rich PPR (SPPR) slide-ring structures. In situ oxidation of thiols creates disulfide bridges between threaded SHCD, crosslinking SPPR into soft hydrogels. To add stoppers to the polymer ends, PEG terminated with thiols (SHPEG) was used to replace PEG in this work. In this case, the oxidation of thiols leads to disulfide connections between SHPEG terminals with other polymers, threaded SHCD, or unthreaded SHCD, which will prevent SHCD from unthreading and convert SPPR to poly(disulfide)rotaxane (PSR). Owing to the sliding of SHCD on the axis, PSR hydrogels display remarkable stretchability and significantly higher toughness than the SPPR hydrogels because the polymer ends of PSR were capped and SHCD could not unthread from the axis under stress. Furthermore, the reversible stretchability of PSR hydrogels strongly depends on polymer entanglement, which applies topological restrictions on the deformation of PSR supramolecular structures and promotes the recovery. Thus, except for the static structures formed in these gels, this work also plans to conduct in situ hydrogel-stretching SANS studies to characterise the structural evolution under tensile deformation and its recovery.