Calorimetric Analysis of Free‐Radical Polymerization Kinetics of Methyl Methacrylate: Effect of TSI‐POSS

The free‐radical polymerization behavior of methyl methacrylate (MMA) is investigated in the presence and absence of trisilanol isobutyl polyhedral oligomeric silsesquioxane (TSI‐POSS) at 70°C and 80°C using a calorimetric approach based on continuous temperature monitoring. The reaction temperature is experimentally recorded, and the corresponding heat flow is estimated from an energy balance, enabling the calculation of monomer conversion and polymerization rate ( R p ) as functions of time. The experimental data are further analyzed to estimate the k t /k p 2 ratio (ratio of the termination to the squared propagation rate coefficients), which serves as a comparative indicator of changes in the balance between termination and propagation. The results reveal a non‐monotonic evolution of the k t /k p 2 ratio, characterized by an initial decrease followed by an increase and a subsequent decline, suggesting behavior consistent with diffusion‐controlled polymerization regimes. The presence of TSI‐POSS is associated with a decrease in the polymerization rate and an increase in the k t /k p 2 ratio, suggesting the influence of diffusion‐related limitations on the polymerization process. These observations are qualitatively consistent with diffusion‐related effects, although independent characterization would be required to confirm the underlying mechanisms.