Particle activation/deactivation effect in RAFT emulsion polymerization of styrene
The seeded RAFT emulsion polymerization of styrene at low initiator concentrations was modelled using population balance equations and Monte Carlo simulations. Without any adjusting parameter, the models accurately predicted the polymerization kinetics, particle size, particle size distribution (PSD), and the characteristic changing trend of molecular weight distribution (MWD) at various initiator concentrations. An initiator concentration-dependent particle activation/deactivation process (PADeP), which played a decisive role in PSD and MWD at very low initiator concentrations, was highlighted to account for the unexpected simultaneous increase in the dispersities of PSD (PDIPS) and MWD (PDIMW) with the decrease of the initiator concentration. It was concluded that at low initiator concentrations, both PDIPS and PDIMW should be mappings of the dispersity of the number of PADeP experienced by particles during the whole polymerization course. The random nature of PADeP caused the dramatic increases in both PDIPS and PDIMW with the decrease of the initiator concentration. However, in the cases of higher initiator concentrations where the average number of PADeP was above 15, the effect of PADeP became much weaker. In such cases, PDIMW should be mainly controlled by the RAFT reaction.