Synthesis, characterization, and influence of synthesis parameters on particle sizes of a new microgel family

Poly(p‐nitrophenylacrylate‐co‐methacrylamide) and poly(p‐Nitrophenylacrylate‐co‐N,N′‐isopropylacrylamide) reactive microgels were synthesized by precipitation polymerization. The process was followed qualitatively by infrared spectroscopy (ATR‐FTIR) and microgels composition was determined by nuclear magnetic resonance (1H NMR). Scanning electron microscopy of obtained colloidal particles showed strictly spherical morphologies with a moderate polydispersity. The average hydrodynamic particle diameter and particle size distributions were measured by quasi‐elastic light scattering and the particle size distributions obtained ranged from 100 to 600 nm. Several synthetic parameters affect the particle size of these materials and thus, indirectly, their properties and future applications. In this article, we report the influence of different polymerization reaction conditions in the final microgel dimensions. For example, we observed that the different solvent‐comonomer affinity induced a significant change in swollen particle size of the copolymeric microgels. On the other hand, the crosslinking density limited the particle sizes, but an excess of crosslinker content in the reaction mixture resulted in the opposite effect. Finally, we also studied the influence of initiator content in the mean particle size. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3833–3842, 2007 Precipitation polymerization is an easy method to obtain monodisperse nanometric crosslinked microgels. Poly(NPA‐co‐MeAM) and poly(NPA‐co‐NIPA) reactive microgels were synthesized by this method. These microgels are able to form colloidally stable dispersions. SEM micrographs (see Figure) show strictly spherical particles with a moderate polydispersity. The particle size distributions measured by light scattering ranged from 100 to 600 nm. It is important to notice that several synthetic parameters can affect the particle size of these materials and thus, indirectly, their properties and future applications. One of these parameters is the crosslinking density (see Figure): it limits microgel swelling and thus, the particle sizes, but an excess of crosslinker content can increase the physical dimensions of the dry microgels, which can be relevant in the final particle sizes of the swollen microgels, even more than the decrease in the swelling capacity.