Optimization of MechanoATRP through ZnO Loading and Reaction Temperature

Mechanically mediated atom transfer radical polymerization (mechanoATRP) has emerged as a promising approach for the controlled synthesis of well-defined polymers, enabled by activator (re)-generation through mechanical stimuli. Besides spatiotemporal control, mechanoATRP enables more uniform generation of electrons owing to the excellent penetration depth of ultrasonic shock waves. However, despite recent progress, the effects of temperature and active particle loading on mechanoredox efficiency remain underexplored. Herein, we present a systematic investigation of how reaction temperature and loading of mechanotransducers jointly govern polymerization kinetics and control in the mechanoATRP of methyl acrylate. ZnO nanocrystals, synthesized via a rapid microwave (MW)-assisted route, were employed as active agents. To decouple thermal and mechanochemical contributions, we designed an ultrasonic setup capable of maintaining precise isothermal conditions during mechanoATRP. By combining experimental techniques, kinetic analysis, and Arrhenius evaluation, the operational limits of mechanoATRP were identified, and the apparent propagation rate constant and apparent activation energy were determined and correlated with both temperature and ZnO loading. The results indicated that the apparent activation energy is strongly dependent on ZnO loading, reflecting changes in the efficiency of mechanochemical catalyst activation. The ZnO loading of 1.0 wt % was identified as the optimum dosing across the temperature range of 25-45 °C, providing high polymerization rates and excellent control over the kinetics. This study provides quantitative insight into the mechanoredox activation mechanism, yielding optimizations of mechanoATRP and advancing its potential toward scalability and energy efficiency.