Direct and Reversible Transformations between Intermolecular Polymer Networks and Single-Chain Nanoparticles Based on Thermally Dissociable Bis(hindered amino)disulfide Linkages

We report a direct topological reorganization between intermolecularly cross-linked polymers and single-chain nanoparticles (SCNPs) via thermal exchange reactions based on bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS) linkages. The network architecture of cross-linked poly(hexyl methacrylate) incorporating BiTEMPS at the cross-linking points can be directly transformed to SCNPs merely by heating in a dilute solution. Diffusion-ordered NMR spectroscopy and GPC analyses confirmed the smaller hydrodynamic radii of the SCNPs compared to those of the chain polymers obtained by de-cross-linking the original networks. The reverse transformation from the SCNPs to the polymer networks was achieved simply by heating under solvent-free conditions. Time-course monitoring of the storage moduli showed a clear increase as a function of heating time due to the restoration of the intermolecular cross-links via disulfide-exchange reactions. The restored cross-linked polymers exhibited comparable cross-linking densities and mechanical properties to those of the original cross-linked polymers, and the properties were again replicated well after an additional network-SCNP transformation cycle. Such an on-demand network-modulation feature enables a postsynthetic adjustment of the elastomer properties by, e.g., fusing SCNPs prepared from cross-linked polymers with different cross-linking densities.