Effect of SiO₂ Nanoparticles on PNVCL Polymerization and Molecular Weight Control

This study investigates the use of SiO₂ nanoparticles as functional modifiers in the polymerization of poly-(<i>N</i>-vinylcaprolactam) (PNVCL), aiming to tailor the polymer's molecular weight and physicochemical and rheological behaviors. The incorporation of nanoparticles into polymerization systems has emerged as a promising strategy to modulate the reaction kinetics and polymer chain growth. In this work, SiO₂ nanoparticles (∼18 nm) were synthesized via the Stober method, incorporated into the radical polymerization reaction of PNVCL at a concentration ranging from 0.5 to 3.0%, and recovered post synthesis. Gel permeation chromatography results revealed that increasing the nanoparticle concentration led to a notable rise in the weight-average molecular weight from 33 to 70 kDa. Rheological analysis revealed that the materials exhibited a predominantly viscous behavior (<i>G</i>″ > <i>G</i>') both below and above the lower critical solution temperature, suggesting incomplete gelation transitions. These findings demonstrate that SiO₂ nanoparticles can act as polymerization modulators, enabling control over molecular weight distribution and viscoelastic properties, with relevance for thermoresponsive systems for drug delivery and related biomedical technologies.