Synthesis of Uniform Polymer Microparticles with Controlled Morphologies by Using Dispersion Polymerization and Consecutive Phase Control Methods

Abstract

This study introduces a straightforward and robust polymerization method for the synthesis of uniform polymer microparticles having controlled surface chemistry as well as tailored particle shapes. Uniform polystyrene (PS) microparticles are produced by dispersion polymerization, in which amphiphilic poly (ethylene oxide)-b-poly (-caprolactone) (PEO-b-PCL) copolymers anchor on the growing polymer particles and stabilize them by the steric repulsion effect. We have observed that when PEO-b-PCL copolymers are incorporated at a proper concentration range, the total number of particles remains unchanged after the formation of primary particles, which is essential for maintaining size uniformity. Otherwise, non-uniform PS microparticles are produced due mainly to the coagulation or secondary formation of particles. To show the diversity of our particle synthesis technology, shape-controlled microparticles, such as dimples and Janus particles, are also produced by using the temperature-mediated swelling and phase separation. Finally, we show that PEO-b-PCL copolymers play a key role in regulating the surface wettability of the seed particles, thereby facilitating formation of anisotropic microparticles. In our continued study, we introduced a useful approach for the fabrication of hollow-structured hydrogel microparticles and for the encapsulation of biomacromolecules in the hollow core of the particles. Monodisperse hollowstructured poly (vinyl amine) hydrogel particles were fabricated without using templates that combines the dispersion polymerization and the sequential hydrolysis/crosslinking. The hydrogel shell showed pH-dependent mesh sizes; ~2 nm at a normal condition (pH 3-12) and 11 nm at an expanded condition (pH 2). By taking advantage of pH-responsive mesh property, we demonstrated that dextran macromolecules, whose hydrodynamic radius is between the mesh sizes of the normal and expanded pH conditions, could be encapsulated and stored inside of the shell. Moreover, our hydrogel particles showed strong adhesion to human cells. Some of them were even engulfed by the cell membrane and drawn into the cell even with no aid of site-specific moieties. From these results, it is expected that the hydrogel hollow microcapsules synthesized in this study could be used for delivery of macromolecules into the cells.