Mechanochemical H-Bonding Organocatalysis Enabled Controlled Synthesis and Recycling of High-Molecular-Weight...

The use of organocatalysts for the ring-opening polymerization (ROP) to achieve high-molecular-weight poly(ε-caprolactone) (PCL) remains challenging. In this study, we present a mechanochemical hydrogen-bond-catalyzed ROP (mechano-HROP) strategy. This approach combines a tris-urea/base co-catalysis together with ball milling to achieve rapid and controlled solid-state polymerization of ɛ-caprolactone (ɛ-CL) at room temperature. The mechano-HROP demonstrated exceptional polymerization activity (k_obs = 0.053 min^-1) while suppressing transesterification reactions compared to conventional bulk ROP. This method enabled the complete conversion of monomers into high-molecular-weight PCLs with M_n up to 185.0 kDa and narrow distribution (Ð < 1.28). The PCL synthesized via mechano-HROP exhibited high chain-end fidelity, as evidenced by MALDI-TOF analysis and successful chain extension from its active chain ends. Density functional theory calculations confirmed the presence of an intramolecular hydrogen-bonding self-activated imidate species under solvent-free condition. Furthermore, we introduced a mechanochemical methanolysis method for PCL recycling under solvent-free and room temperature conditions. Kinetic comparisons with stirred methanolysis highlight the efficiency of mechanochemistry in PCL depolymerization. In summary, this work establishes a highly efficient mechanochemical route for the synthesis and recycling of high-molecular-weight PCLs.