Fatemeh Jahanzad

Semicontinuous monomer-starved emulsion polymerization as a means to produce nanolatexes: analysis of nucleation stage.

In this research, particle nucleation was decoupled from particle growth in the monomer-starved semicontinuous (micro)emulsion polymerization of styrene by close monitoring of the end of nucleation. This enabled us to exclude the effects of particle growth on nucleation and therefore unravel inherent features of nucleation in this process. Nanolatexes with average particle sizes as small as 15 nm were obtained. The average size of particles at the end of nucleation was found to be almost independent of surfactant concentration ([S]) but varied with the rate of monomer addition (Ra) to the 1/3 power. Nucleation time varied almost proportionally with [S](1.0). The sharpest particle size distribution was obtained at the lowest monomer feed rate used. The weight-average molecular weights (M̅w) of the polymer produced decreased with decreasing Ra. A simple correlation was developed which shows that the number-average molecular weight (M̅n) is proportional to Ra(1.0) but independent of [S] (i.e., [S](0.0)), which was in fair agreement with the experimental results. It is also shown that the polymer molecular weight is proportional to the average volume of particles; the smaller the particle, the lower the molecular weight.

Comparative study of monomer droplet nucleation in the seeded batch and semibatch miniemulsion polymerisation of styrene

Abstract Monomer droplet nucleation in the seeded miniemulsion polymerisation of styrene under monomer-flooded and monomer-starved conditions was studied. The miniemulsion feeds were added to the reactor either batchwise or semibatchwise. The droplets preserved longer under flooded conditions. As a result, the batch operation led to a larger number of particles (Np) than the semibatch operation. For the miniemulsion droplets containing predissolved polymer, the final Np was independent of the way that the feed was added to the reactor and was equivalent to the number of monomer droplets in the original miniemulsion feed. The size distribution of the final latexes, however, was influenced by the operation type. For the batch operation, the rate of polymerisation (Rp) with the miniemulsion feeds was higher than that with the conventional monomer emulsion feed because of the monomer droplet nucleation. But for the semibatch operation, the opposite was true because of Rp controlled by the rate of monomer diffusion from rather stable miniemulsion droplets to the growing polymer particles.