One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(N-vinyl formamide)

Abstract

In this study we report the preparation of a new family of core-shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core-shell PNVF-xGMA [poly(N-vinylformamide-co-glycidyl methacrylate)] particles (where x is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable "cane-ball"-like morphology with interconnected ridges, and this could be controlled by the value for x. The particle size was tunable over the range 0.8-1.8 μm. Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by x. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-xGMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels.