Low friction in lubricated mechanical components is in part enabled by protective films that form at sliding interfaces during operation. These films are formed through chemical reactions between additive molecules in the lubricant and the surfaces, where the reactions are driven by mechanical force exerted by the sliding bodies. Despite the presence of tribofilms in most moving components, the mechanisms of film formation are still poorly understood, primarily because the process occurs inside a moving contact, which typically limits experimental approaches to pre- and post-sliding surface analyses. Although such experiments cannot directly reveal reaction pathways, they can be complemented by reactive molecular dynamics simulations that model chemical reactions between additive molecules and surfaces at the atomic scale. We use this approach to investigate shear-driven polymerization of molecules adsorbed on silica surfaces, a model system that enables identification of shear-driven reaction pathways. The results show that interfacial shear not only accelerates polymerization reactions but opens reaction pathways that are not accessible thermally. Specifically, the simulations reveal that chemisorption and shear-induced deformation of the reactants are critical steps in tribochemical processes. These findings improve our understanding of tribofilm formation mechanisms and, more generally, may form the basis for design of systems where shear force can be leveraged to tune or lower the energy cost of chemical reactions.