Solvent-Free Chemical Recycling of Polymers made by ATRP and RAFT polymerization: High-Yielding Depolymerization at Low Temperatures

Although controlled radical polymerization is an excellent tool to make precision polymeric materials, reversal of the process to retrieve the starting monomer is far less explored despite the significance of chemical recycling. Current depolymerization approaches typically require elevated temperatures (>350 ˚C), high dilutions in specific solvents (typically 0.1-25 mM polymer concentrations), and/or expensive catalysts. Here, we report that RAFT-synthesized polymers can undergo a low-temperature solvent-free depolymerization back to monomer thanks to the partial in-situ transformation of the RAFT end-group to macromonomer. To aid a more complete depolymerization, we performed a facile and quantitative end-group modification strategy with the modified RAFT polymers exhibiting significantly higher depolymerization conversions (~90%) at comparable temperatures. The end-group transformation was applied to polymers synthesized by ATRP triggering an efficient low-temperature bulk depolymerization (~90% of monomer regeneration) with an onset at 150 ˚C, in contrast to previous reports where depolymerization could only be triggered at much higher temperatures (> 350 ˚C). The versatility of the methodology was demonstrated by a scalable depolymerization (~10 g of starting polymer) retrieving 84% yield of the starting monomer intact which could be subsequently used for further polymerization. This work presents a new low-energy approach for depolymerizing controlled radical polymers and creates many future opportunities as high-yielding, solvent-free and scalable depolymerization methods are sought.