Biodegradable poly(disulfide)s derived from RAFT polymerization: monomer scope, glutathione degradation, and tunable thermal responses.

Telechelic, RAFT (reversible addition-fragmentation chain transfer)-derived macromonomers with a pyridyl disulfide end-group were converted into high molecular weight, disulfide-linked polymers using a polycondensation, step-growth procedure. The applicability of the method to polycondense a library of macromonomers with different functionalities including (meth)acrylates and acrylamides was investigated. Side-chain sterics were found to be important as nonlinear poly(ethylene glycol) analogues, which proved incompatible with this synthetic methodology, as were methacrylates due to their pendant methyl group. This method was used to incorporate disulfide bonds into poly(N-isopropylacrylamide), pNIPAM, precursors to give dual-responsive (thermo- and redox) materials. These polymers were shown to selectively degrade in the presence of intracellular concentrations of glutathione but be stable at low concentrations. Due to the molecular weight-dependent cloud point of pNIPAM, the lower critical solution temperature behavior could be switched off by a glutathione gradient without a temperature change: an isothermal transition.