Synthesis of Polymer Microspheres via Self-Assembly of Monodisperse Precursor Particles

Spherical monodisperse vinyl copolymer particles have been prepared using three different techniques: surfactant-free emulsion polymerization (SFEP), precipitation polymerization (PP), and dispersion polymerization (DP). SFEP yielded methacrylic acid (MAA)−styrene (St) (MAA/St = 25/75) copolymer particles with a diameter of ∼200 nm. PP yielded MAA−divinylbenzene (DVB) copolymer particles with a diameter of ∼5 μm (MAA/DVB = 25/75) and of ∼1 μm (MAA/DVB = 60/40), and also glycidyl methacrylate (GMA)−DVB (GMA/DVB = 60/40) copolymer particles with a diameter of ∼4.5 μm. DP was used to prepare GMA−St (60/40) copolymer particles of diameter ∼1.5 μm. Attempts to self-assemble samples of each primary particle into spherical aggregates were made using high solids (33%) aqueous dispersions each in inverse suspension in toluene. Self-assembly was induced by Dean−Stark removal of the water in some of the toluene. No success was achieved with the two largest sized particles. However, both the ∼200 nm and the two 1−1.5 μm primary particles were successfully self-assembled into spherical aggregates provided the particles were functionalized with hydroxyl or carboxylic acid groups. The aggregates were further chemically modified in an attempt to improve the stability of each, and then all of the self-assembled materials were tested for stability in contact with a broad range of solvents. The “as-formed” aggregates are stable in nonpolar solvents and water but have poorer stability in solvents of intermediate polarity. However, the chemically treated analogues are stable in the broad range of solvents tested.