Microwave-assisted aqueous MMA polymerization over TiO₂ nanotubes decorated with vanadium complexes

Abstract

The simultaneous achievement of ultra-high catalytic turnover and precise structural control remains a fundamental challenge in sustainable macromolecular synthesis. Herein, we report a highly efficient, eco-friendly, and energy-minimized microwave-assisted catalytic system for the radical polymerization of methyl methacrylate (MMA). This approach utilizes surfaceengineered, metal-leaching-free nanocomposites based on dipicolinate vanadium(IV) complexes (VO(dipic)(L), where L = 2,2'-bipyridine or 1,10-phenanthroline) immobilized on anodized TiO₂ nanotubes.By leveraging the microwave field as a non-thermal kinetic regulator, these heterogeneous systems exhibit unprecedented catalytic activity in pure water, reaching turnover frequencies a twenty-fold enhancement compared to conventional, energy-intensive thermal conditions (TOF > 11,300 h⁻¹). The resulting polymers possess narrow molecular weight distributions and a strictly linear microstructure. Post-reaction surface analysis (XPS, SEM) and polymer characterization (FTIR, GPC, NMR) confirm a "grafting-from" mechanism. Multivariate principal component analysis (PCA) statistically confirms that the microwave field acts as a primary driver for a kinetic regime that decouples polymerization rate from termination probability. This work demonstrates that rationally designed heterogeneous catalysts, when coupled with alternative energy sources and aqueous media, can overcome the classical rate-selectivity tradeoff, offering a scalable and sustainable route to high-performance functional materials without the ecological burden of traditional transition-metal catalysts.