Controlled Atom Transfer Radical Depolymerization.

Atom transfer radical polymerization is a versatile controlled radical polymerization methodology in which control over polymerization is achieved by shifting the activation-deactivation equilibrium towards dormant species, leading to polymers of targeted molecular weight and dispersity. However, the chemical recycling of ATRP materials lacks this level of control, with current methodologies favoring rapid end-group activation over deactivation, resulting in an uncontrolled depolymerization whereby polymer chains unzip completely without any molecular weight control. In this work, the first example of controlled ATRP depolymerization is realized by strategically promoting deactivation over both activation and depropagation. The controlled nature of the reaction is achieved by increasing catalyst concentrations and reducing temperatures, resulting in on-demand and uniform shortening of the polymer chains during the depolymerization, as evidenced by a linear decrease in molecular weight with conversion. Furthermore, while the uncontrolled depolymerization of diblock copolymers results in the simultaneous release of both monomers, controlled depolymerization leads to selective regeneration of the second block, where the monomer closer to the halogen end-group is preferentially released first, thus providing a powerful analytical handle for structural characterization. The versatility of this strategy is confirmed across various activation mechanisms, including thermal, photochemical, and initiators for continuous activator regeneration (ICAR) ATRP.