Thiol-Functionalized TiO₂ as Reactive Nanoadsorbents for Residual Monomer Removal from Waterborne Polymer Dispersions

This study explores the use of thiol-functionalized TiO₂ nanoparticles to reduce residual methyl methacrylate (MMA) and butyl acrylate (BA) monomers in waterborne polymer dispersions (latexes). TiO₂ nanoparticles were modified with (3-mercaptopropyl)-triethoxysilane (MPTES) to introduce -SH groups capable of thiol-ene type reaction with CC bonds of monomers. The effects of functionalization density, nanoparticle concentration, and mixing time on monomer removal were systematically evaluated. Compared with unmodified TiO₂, MPTES-modified nanoparticles achieved up to 90% removal of MMA and nearly complete removal of BA, lowering total residual monomer content from ∼1900 ppm to 120 ppm. About 80-90% of the adsorbed monomers were chemically, thus, irreversibly bonded to the TiO₂ surface. DLS, TEM, and zeta potential analyses revealed improved dispersion and reduced aggregation of modified nanoparticles in the latex, leading to uniform distribution in films obtained by water evaporation. TEM imaging further showed preferential localization of modified TiO₂ at the polymer particle surfaces, enabling efficient monomer capture while maintaining good dispersion. The resulting films displayed unchanged water sensitivity but significantly improved mechanical properties, with Young's modulus increasing by 75%. Overall, thiol-functionalized TiO₂ nanoparticles act as reactive, multifunctional adsorbents that effectively reduce residual monomer content and enhance the mechanical performance of MMA/BA polymer latex coatings.