SET-LRP from Programmed Difunctional Initiators Encoded with Double Single-Cleavage and Double Dual-Cleavage Groups

The use of stimuli-cleavable difunctional initiators containing a discrete single-type cleavable junction represents a general strategy to prepare mid-chain-degradable vinylic polymers. Here, we present a series of α-haloester-type programmed initiators encoding multiple single-type and dual-type cleavable junctions. Multiple single-cleavage groups increase the cleavage rate, whereas double-dual sites provide access to multiple mechanisms for cleavage. Single-electron transfer living radical polymerization was employed to generate well-defined mid-chain-cleavable poly(methyl acrylate)s designed with low-pH, low-pH/reduction, or low-pH/UV light cleavable linkages. Kinetic studies demonstrated that the polymerizations are living when using various catalytic Cu(0) sources (wire and powder), ligands (Me₆-TREN and TREN), and solvent sources (homogeneous and "programmed" biphasic). Moreover, structural analyses by NMR and matrix-assisted laser desorption/ionization-time-of-flight confirmed the near-perfect chain-end functionality of these stimuli-cleavable polymers derived from programmed initiators. A rigorous gel permeation chromatography study demonstrated that the combination of multiple acetal, disulfide, or 2-nitroresorcinol-derived acetal junctions offer attractive possibilities in terms of selective cleavage and orthogonal degradation.