Synthesis and Characterization of Solvent-Invertible Amphiphilic Hollow Particles

Previous researches on solvent-dependent polymer systems mainly focus onamphiphilic invertible polymers (AIPs), which are capable of forming solvent-dependent micellaror inverse micellar assemblies. However, polymer particles that are invertible in response tosolvent polarity are almost unexplored. In this paper, we report a new type of invertible hollowpolymer (IHP) particle that is comprised of polyethyleneimine-g-poly(methyl methacrylate)(PEI-g-PMMA) copolymer. The amphiphilic PEI-g-PMMA hollow particles were first preparedthrough synthesis of well-defined PEI/PMMA core-shell particles, followed by removal of PMMAhomopolymer from the core. The resulting IHP particles can be stably dispersed in both non-polarsolvent and water. We have investigated the morphology and surface property of the particles in both dichloromethane (DCM) and water using transmission electron microscopy, water contactangle measurement, and X-ray photoelectron spectroscopy analysis to gain insight into this uniqueparticle dispersibility. Sustainability of the solvent-invertible property was carefully studiedthrough repeated treatment of the IHP particles in DCM or water for up to six cycles.Solvent-dependant property of the dry films formed by IHP particles was also investigatedthrough water contact angle measurement. Increasing water content on the DCM-treated IHPparticle film could reduce the water contact angle from 94o to 51o. Our results demonstrate that theamphiphilic hollow particles are a new type of polymer design for smart materials that areinvertible in response to non-polar and aqueous media in both dispersed and solid states.