Nonequilibrium morphology development in seeded emulsion polymerization. IV. Influence of chain transfer agent

Abstract

ABSTRACT:We performed a series of experiments to study the effect of a chain transfer agent, n-dodecyl mercaptan (n-DM), on the development of morphology in composite latex particles. The morphologies were determined using a combination of transmission electron microscopy, differential scanning calorimetry, and surfactant titration. The polymer molecular weights were reduced up to 10-fold with n-DM levels up to 1.4% in the monomer. The addition of n-DM can increase the extent to which second-stage polymer domains are formed within the interior regions of the seed particles, but this is only expected under specific conditions. Numerical simulations support this conclusion. We also observed that the reduction in the molecular weight of the second-stage polymer did not significantly increase the extent of phase separation and morphology rearrangement within the particles. The overall effect on the morphology was limited.

Fundamentals of Emulsion Polymerization

“…These effects will now be discussed. The work of Sundberg and co-workers in this area is seminal ,− and will be followed here in descriptive (rather than mathematical) terms in order to convey the important concepts.…”

Coupling HAADF-STEM Tomography and Image Reconstruction for the Precise Characterization of Particle Morphology of Composite Polymer Latexes

“…This is a challenging goal because the morphology is created during the polymerization as a result of complex interactions between kinetics and thermodynamics involved in the polymerization. − Currently, the production strategies used commercially are largely based on extensive experimental work guided by a rich literature on the effect of the operation variables on the final particle morphology. ,,,− However, it is open to discussion whether this approach would be sufficient in a search for a globally optimal strategy. Thus, by use of a mathematical model for the process, it has been recently demonstrated in silico that the optimal strategies may involve complex profiles of temperature and monomer feed rate, which are unlikely to be obtained by the currently used approach.…”

Effect of Molecular Weight on the Morphology of Polystyrene/Poly(methyl methacrylate) Composite Particles Prepared by the Solvent Evaporation Method

“…The molecular weight of the polymer is one of the crucial parameters in determining the nonequilibrium morphology of composite particles during seeded emulsion polymerization. The molecular weight of the polymer determines the diffusion rate of the polymers formed in the second polymerization steps at a certain weight fraction of polymer, and this affects the final particle morphology. − However, the effect of molecular weight on the thermodynamic equilibrium morphology has been disregarded so far. The molecular weight barely affects the interfacial tension between polymer and aqueous phases when the molecular weight of polymer is higher than approximately 2.5 × 10 3 .…”