Colloidal vinvl polymer-silica nanocomposite particles are synthesized with very high silica aggregation efficiencies via aqueous emulsion using a cationic azo initiator in the presence of a glycerol-functionalized ultrafine aqueous silica sol as the sole stabilizing agent (see scheme). The protocol is surfactant-free and requires neither auxiliary comonomer nor nonaqueous co-solvent. The particles are film-forming at ambient temperature, yielding highly transparent films containing up to 39% silica by mass.