Particle size and molecular weight distributions of various polystyrene emulsions

Abstract

Three different emulsion polymerization techniques, the batch (B), monomer addition (M Add), and emulsion addition (E Add) procedures were studied. Rates of polymerization indicated that the B reacted more rapidly than either the M Add or E Add. This was related to the lower monomer concentration present in the M Add and E Add systems. This is described as monomer starvation. MW and MW distributions were compared for these polymers. The B polymer had a significantly higher MW than either the M Add or E Add polymer. This could also be related to monomer starvation in the latter systems. However, the MW distribution of these polymers gave comparable values of Mw/Mn = 3.1. This indicates a similar molecular growth phenomena which appears to result from polymerization occurring near the particle surface for the addition systems. Particle size distribution measurements showed the B latex to have the narrowest distribution while the E Add latex had the widest. Also, the M Add had a particle diameter distribution which was approximated by a normal distribution. This is explained by use of the monomer starvation concept. Additional polymerizations were carried out called “hybrids” which were variations of the polymerizations discussed above. Significant differences result from the various techniques of emulsion polymerization. These differences manifest themselves not only in average particle size and MW, but also in particle size distribution. No significant differences were obtained in MW distributions.

Development of glycine immunoreactivity in the brain of the sea lamprey: Comparison with γ‐aminobutyric acid immunoreactivity

“…A simple calculation shows that for the lowest addition rate (0.068 g/min), particles should have grown from 16.5 nm at 12% conversion to ∼34 nm at 91% conversion, if all the monomer would have been used in the growth process; instead particles grew from 16.5 to 20 nm in the same conversion interval. This behavior clearly demonstrates the predominance of nucleation of new particles over the growing mechanism of the existing ones, which is typical of monomer‐starved semicontinuous addition 18…”

“…Because the accumulation of monomer within the particles favors their growth in detriment of formation of new particles,18 N P diminishes as F m increases (Fig. 6).…”

“…The reports on semicontinuous microemulsion polymerization indicate that this operation mode leads to an increase in the polymer/surfactant ratio, keeping particle size in the range of that of batch microemulsion polymerization 9–16. Nevertheless, to minimize particle size and surfactant in this type of heterogeneous polymerization, it is necessary to operate under the so‐called monomer‐starved conditions during the addition period 18. Krackeler and Naidus,18 who introduced this concept, invoked the correlation developed for emulsion polymerization by Smith and Ewart19 for predicting the number of particles ( N P ) for the case‐II kinetics, in which N P is inversely proportional to the volume growth rate of polymer particles during nucleation period, to explain the reduced particle growth and the formation of a large number of polymer particles in the emulsion polymerization of styrene carried out in semicontinuous mode compared with the batch process.…”

Natural Gum Reduced/Stabilized Gold Nanoparticles for Drug Delivery Formulations

“…First, the literature data are not often precise regarding the conditions under which the particle formation occurred. In some instances when the process used was a semibatch polymerization, the particle formation mostly occurred either under monomer‐flooded conditions or during the early stages of monomer‐starved conditions 15–17. Second and more importantly, in most research reported in the literature regarding particle formation at a high conversion, common anionic emulsifiers, such as sodium alkyl sulfates [e.g., sodium lauryl sulfate (SLS)], have been used 18, 19.…”

Semicontinuous heterophase copolymerization of styrene and acrylonitrile

“…5) with monomer addition indicate that most of the added monomer is used to form new particles and not for the growth of the existing ones. In fact, it has been reported for the semicontinuous emulsion polymerization under monomer‐starved conditions, that particle nucleation predominates over the growing of particles 38, 48…”