Cross-linked polymer microparticles with tunable surface properties by the combination of suspension free radical copolymerization and Click chemistry

Abstract

We propose a general, versatile and broad in scope two-steps approach for the elaboration of cross-linked polymer microparticles (µPs) with tunable surface properties and functionalities. Surface-functionalized cross-linked polymer µPs with diameter in the 80 μm range are prepared by the combination of: 1) suspension free radical copolymerization of styrene, propargyl methacrylate and 1,6-hexanediol dimethacrylate, 2) subsequent covalent tethering of a variety of azide-functionalized moieties by copper(I)-catalyzed azide-alkyne cycloaddition (i.e. rhodamine B fluorescent dye or poly(ethylene glycol) brushes) and, 3) optional N-alkylation of the 1,2,3-triazole groups followed by anion exchange reactions to afford covalently-tethered 1,2,3-triazolium ionic liquids with iodide or cresol red as counter-anions. The resulting µPs are characterized by laser diffraction, differential scanning calorimetry, as well as by optical, confocal fluorescence, scanning electron and atomic force microscopies. Finally, the rheological properties of concentrated suspensions (volume fractions of 0.40 and 0.44) of the different synthesized µPs dispersed in a 1:1 (vol/vol) mixture of polalkylene glycol and water are studied.The modification of particles surface properties contributes not only to change the stability of the suspensions against flocculation, but also to significantly modify their rheological behavior at high shear stresses. This last result highlights the importance of non-hydrodynamic contact forces in the rheology of non-Brownian suspensions.