Studies of microgel formation in aqueous and organic solvents by light scattering and analytical ultracentrifugation

Abstract

Fourteen nearly monodisperse aqueous poly-n-butylmethacrylate (PBMA) dispersions with diameters of about 60 nm were prepared by emulsion polymerization. These PBMA-dispersions contain different amounts of the crosslinker methallylmethacrylate (MAMA), p _MAMA=0/0, 02/0, 04/0, 06/0, 08/0, 1/0, 2/…/10 wt.%.

First, these aqueous dispersions were characterized by light scattering (LS) and analytical ultracentrifugation (AUC). Particle size distributions, diffusion coefficients, sedimentation coefficients and particle densities were determined.

Then these PBMA/MAMA-particles were transferred directly into the organic PBMA-solvent tetrahydrofuran (THF). Particles with small amounts of MAMA are completely dissolved, whereas particles with high amounts of MAMA are completely crosslinked and exist as swollen microgel particles with varying volume swelling ratios, q. Particles with medium amounts of MAMA consist of both dissolved macromolecules and crosslinked, extremely swollen microgels. Also by LS and AUC, the molecular masses, diffusion coefficients, sedimentation coefficients and densities of the dissolved macromolecules and the microgel particles were measured. Further, both the wt.%-ratio of dissolved macromolecules/microgel particles and the swelling ratio q of the microgel particles were determined.

The measured quantities are discussed in relation to existing crosslinking theories. The hydrodynamic behavior of microgel particles in the interesting transition region from dissolved macromolecules to crosslinked particles is also discussed.