Organic-inorganic hybrid nanocomposites are considered a new generation of high performance materials because they combine both the advantages of inorganic materials (stiffness, high thermal stability, barrier properties, optical, catalytic, electrical and thermal conductivity among others) and organic polymers (flexibility, dielectric, toughness, lightweight, processing). Each part of a nanocomposite has a synergistic function in its performance and has much better combination properties than a single material. We report on the thermo-mechanical properties and morphology of polyacrylic-nanosilica (SiO2) composites prepared in-situ via emulsion polymerization, using a semi-continuous mode. The latex emulsion thus obtained was stable for at least six months. Moreover, this process produced controlled molecular weight in the final latex and low formation of agglomerates. Films drawn from the latex exhibited excellent optical transparency, suggesting good dispersion of the nanosilica, and confirmed by scanning electron microscopy (SEM). There was an increase in glass transition temperature, Tg, suggesting a modification of molecular dynamics; hydrophobic behavior, as probed by water contact angle, was also promoted. Moreover, the Young’s modulus of the nanostructured latex films increased up to 57% with only 3 wt% nanosilica, therefore denoting a reinforcing effect of the nanoparticles.