Production of multihollow polymer particles by the stepwise alkali/acid method IV. Acid treatment process

Multiblock copolymer synthesis via aqueous RAFT polymerization-induced self-assembly (PISA)

Employing RAFT PISA emulsion polymerization to synthesize high molecular weight hexablock multiblock copolymers.

Role of Osmotic Pressure for the Formation of Sub-micrometer-Sized, Hollow Polystyrene Particles by Heat Treatment in Aqueous Dispersed Systems †

In a previous article, it was reported that a rather amount of sulfate end-groups as initiator fragment were buried in the inside of polystyrene (PS) particles, which were synthesized by emulsion polymerization with potassium persulfate initiator and nonionic emulsifier and operated to absorb water from the aqueous medium, resulting in hollow particles, when the PS emulsion was treated at higher temperature than the glass transition temperature of PS. In this article, it was clarified that the water absorption is based on the osmotic pressure between the outside (aqueous medium) and inside of the PS particles due to the buried sulfate end-groups.

Preparation of Flattened Cross-Linked Hollow Particles by Suspension Polymerization in a Solid Dispersion Medium

Flattened cross-linked hollow poly(divinylbenzene) (PDVB) particles with encapsulated n-hexadecane (HD) were successfully prepared through suspension polymerization using the self-assembling of phase-separated polymer (SaPSeP) method, in which the solid dispersion medium was gelled by gellan gum and compressed. The solid phase induced by gellan gum can be easily changed to a liquid state by heating, allowing the obtained particles to be easily recovered after polymerization. When the polymerization was conducted in the solid dispersion medium without compression, spherical hollow PDVB/HD composite particles were obtained. In contrast, when the polymerization was conducted with the compression of the solid dispersion medium, flattened hollow PDVB/HD composite particles were obtained. The shape of the flattened hollow polymer particles was controlled by changing the compression ratio of the solid phase, and the size could also be controlled by changing the DVB/HD droplet size using the Shirasu porous glass membrane-emulsification technique. Furthermore, flattened hollow particles larger than 20 μm in size were obtained, but it was difficult to obtain spherical hollow particles of such large size using the SaPSeP method.

The generation of void morphology inside soap-free P(MMA-EA-MAA) particles prepared by seeded emulsion polymerization

Monodisperse soap-free P(MMA-EA-MAA) latex particles were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and methacrylic acid (MAA), and the particles with void morphology were obtained after undergoing alkali post-treatment. Effects of treatment conditions on particle morphology were investigated. Results showed that the void particles can be obtained under the conditions of the temperature >60 degrees C, initial pH >10.0, treatment time >20 min and 2-butanone amount >2.0 ml. The particle volume and the void size increased to the maximum and then decreased with the increases of initial pH and the treatment time, and these two values increased monotonously with the treatment temperature or 2-butanone amount increased. When the treatment temperature was elevated to 90 degrees C, the treatment time was longer than 180 min, or the 2-butanone amount was more than 8.0 ml, the relatively small voids inside most of the particles combined together to form a large one. The void structure disappeared completely as the initial pH was higher than 12.0. The generation mechanism of the void morphology was discussed.

Hydrophobic Core/Hydrophilic Shell Amphiphilic Particles

Amphiphilic colloidal particles with hydrophobic cores and hydrophilic shells were prepared via a two-step method. First, polystyrene cores were obtained through the concentrated emulsion polymerization. A mixture of styrene, ethyl benzene, divinyl benzene, azobisisobutyronitrile, and cumene hydroperoxide (CHPO) was partially polymerized at 80 degrees C for 40 min and subsequently used as the dispersed phase of a concentrated emulsion in water. The concentrated emulsion was subjected to complete polymerization at 60 degrees C for 12 h; colloidal particles of crosslinked polystyrene were thus obtained. In the second step, the polystyrene particles were dispersed in water, after which acrylamide, N,N'-methylenebisacrylamide, and ferrous sulfate (FS) were added. The system was heated (typically at 30 degrees C) to conduct the polymerization of the hydrophilic monomers. The CHPO present on the surface of the polystyrene particles and the FS present in the aqueous phase (both together constitute a redox initiator) ensured that the initiation occurred mostly on the surface of the particles and that the hydrophilic polymer obtained formed a shell encapsulating the particles. Under proper conditions, a porous outer shell could be generated, making the hydrophobic core accessible to the outside medium. Copyright 2001 Academic Press.