Stirring-Induced Kinetic Retardation in Ethylene Emulsion Copolymerization: Reversible Initiator Complexation Via Collision-Driven Mass Transfer

Abstract

In the emulsion copolymerization of ethylene with polar monomers, vigorous agitation is typically expected to overcome mass-transfer resistance and enhance polymerization yield. In contrast, we report a stirring-induced kinetic suppression, where polymerization activity is reversibly reduced at elevated stirring rates. Through comprehensive kinetic analysis, Raman spectroscopy, and density functional theory calculations, we show that this phenomenon originates from the interplay between hydrodynamic regimes and initiator chemistry. As stirring intensity increases, the mass transfer mechanism shifts from diffusional transport to a collision-dominated regime governed by inertial impaction. This collision-induced contact bypasses the interfacial barrier, promoting the formation of a labile ethylene-persulfate complex that inhibits thermal decomposition without irreversible degradation. The resulting radical-deficient environment leads to a significant increase in copolymer molecular weight and a corresponding reduction in ethylene incorporation. These findings demonstrate that hydrodynamic conditions can affect intrinsic chemical kinetics by triggering latent monomer-initiator interactions, identifying a previously overlooked retardation mechanism in gas–liquid multiphase polymerizations. Theoretical simulations indicate that the complexation is driven by weak C–H···O interactions, which stabilize the initiator by contracting the peroxide bond, thus increasing its thermal homolysis barrier.