Get the full paper here: Macromolecules, 47, 2257 (2014).
Advances in the understanding of microgel properties and exploitation of their full potential for applications require control of the extent and type of functionalization, while at the same time providing control of particle shape, that is, size and uniformity, and intrinsic particle properties such as hardness and degree of crosslinking. However, versatile and simple synthetic approaches to prepare highly uniform and densely functionalized microgels based on functional groups unsuitable for aqueous precipitation polymerization are still scarce. As an alternative platform approach, herein we report on the synthesis of uniform particles based on classical batch emulsion polymerization, which are later postfunctionalized via Cu-mediated Huisgen-type alkyne/azide click chemistry. We use propargyl acrylate (PGA) as a monomer and ethylene glycol dimethacrylate (EGDMA) as a crosslinker for the synthesis of narrowly dispersed latex particles in the size regime of 50–200 nm in radius. We demonstrate how particle hardness and swelling can be tuned as a function of the used ratio of monomer/crosslinker. Postmodifications in the interior of the particles are conducted in the swollen state in DMSO, and we add pH-responsive cationic moieties as a first attractive model functionality. Combined Raman spectroscopy and elemental analysis reveal the kinetics and degree of modification. Both depend on the degree of crosslinking, and we find densely functionalized particles exhibiting a conversion of the alkyne functionalities of up to 90%. After modification, the resulting microgels display a pH-dependent ionization and swelling behavior in water. The suggested route opens up new and versatile ways to prepare narrowly dispersed water-dispersible microgels with tailored hardness and high density of functional groups, based on readily available building blocks.