Low-Temperature Depolymerization of Polymethacrylamides

Abstract

The depolymerization of polymers synthesized by reversible deactivation radical polymerization (RDRP) has recently garnered significant attention due to its potential for recovering monomers at low temperatures. However, current reports focus solely on polymethacrylates, significantly limiting applications, scope, and fundamental understanding. Although polymethacrylamides are highly valued for their excellent biocompatibility, antibacterial properties, and water solubility, their chemical recycling remains experimentally unattainable, irrespective of their synthesis method (i.e., free radical, RDRP, anionic, etc.). Herein, we present the first example of thermal reversible addition-fragmentation chain-transfer (RAFT) depolymerization of various polymethacrylamides, regenerating monomers at high yields. Central to our work was the identification of two key weaknesses associated with polymethacrylamides, namely, i) insufficient end-group activation, and ii) premature end-group loss at higher temperatures, leading to compromised monomer yields and low depolymerization rates. These challenges were bypassed via the addition of commercially available radical initiators, resulting in faster reactions and higher percentages of recovered monomer at as low as 90 °C. The broad applicability of this method was further demonstrated by its compatibility with various RAFT agents, and the possibility to depolymerize a crosslinked hydrogel. Our work expands the depolymerization scope of high-value materials beyond polymethacrylates and shines a light on intriguing thermodynamic and kinetic insights.

Keywords: Depolymerization; Polymers; Polymethacrylamides; RAFT.