Termination Kinetics of Surface-Initiated Radical Polymerization Measured by Time-Resolved ESR Spectroscopy after Laser-Pulse Initiation

Abstract

The single-pulse–pulsed-laser polymerization–electron spin resonance (SP-PLP-ESR) method was used to study the termination reaction in polymerization of n-butyl methacrylate (n-BMA) from silica nanoparticles. The polymerization from the surface was initiated by the surface-attached photoinitiator 2,2-dimethoxy-2-phenyl-1-(2-(2-(trimethoxysilyl)ethyl)phenyl)ethane-1-one (DMPTS). The obtained termination rate coefficient at 335 K of kt = (5.4 ± 0.7) × 106 L mol–1 s–1, which could unambiguously be assigned to the termination reaction between two surface-attached macroradicals, is about 2 orders of magnitude smaller than the value found in homogeneous n-BMA polymerization. Surprisingly, no chain-length dependence of the termination rate coefficient could be observed. This fact and temperature-dependent studies of kt, which yield an activation energy that is in perfect agreement with the activation energy of propagation of n-BMA, indicate that the termination between surface-attached macroradicals proceeds under reaction diffusion control, as their translational diffusion is suppressed.