Study of kinetics and properties of polystyrene/silica nanocomposites prepared via in situ free radical and reversible addition-fragmentation chain transfer polymerizations

A number of batch polymerizations were performed to study the effect of pristine nanoparticle loading on the kinetics of free radical and RAFT polymerizations and properties of polystyrene/silica nanocomposites. To study the kinetics of polymerization, Conversion, molecular weight and polydispersity index (PDI) were monitored during polymerization to investigate the reaction kinetics. According to the results, adding nanoparticles causes no considerable change in the kinetic curves, while there is an optimum value for nanoparticles loading in which the monomer conversion and molecular weight reaches to its maximum level. However, increasing silica content resulted in an increase in PDI values. In comparison with free radical polymerization, monomer conversion and molecular weight were lower for RAFT polymerization. The prepared samples were characterized by thermogravimetric analysis (TGA), Dynamic Mechanical Thermal Analysis (DMTA), and Differential Scanning Calorimetry (DSC). According to TGA results, in free radical samples, one stage of degradation related to the random chain scission is observed while degradation of RAFT nanocomposites has occurred in two steps due to decomposition of RAFT moieties and random chain scission. Also, the best improvement of mechanical and thermophysical properties is achieved for nanocomposites containing 5 wt% silica nanoparticles.