Effects of the kind and concentration of stabilizers on the nonspherical shape of polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles prepared by release of toluene from PS/PMMA/toluene droplets dispersed in stabilizer aqueous solution were examined. In the case of poly(vinyl alcohol), the surfaces of the obtained particles always had a single dimple. In the case of sodium dodecyl sulfate (SDS), the shapes of the composite particles changed from the dimple, via acorn, to spherical with increasing SDS concentration. It was clarified that the dimple and acorn shapes of the PS/PMMA composite particles were caused by contraction of the PS phase after hardening of the PMMA phase in excentered core-shell and hemisphere morphologies, respectively, which were formed by phase separation during toluene evaporation.

Micrometer-sized silica-stabilized polystyrene latex particles and submicrometer-sized polystyrene−silica nanocomposite particles have been prepared by dispersion polymerization of styrene in alcoholic media in the presence of a commercial 13 or 22 nm alcoholic silica sol as the sole stabilizing agent. Micrometer-sized near-monodisperse silica-stabilized polystyrene latexes are obtained when the polymerization is initiated with a nonionic AIBN initiator. These particles are stabilized by silica particles that are present on the latex surface at submonolayer concentration. The total silica content is no greater than 1.1 wt %, which corresponds to a silica sol incorporation efficiency of less than 1.3%. Reduction of the initial silica sol concentration led to a systematic increase in the mean latex diameter. In contrast, submicrometer-sized polystyrene-silica nanocomposite particles are obtained when the polymerization is initiated with a cationic azo initiator. The silica contents of these nanocomposite particles are significantly higher, ranging up to 29 wt %. Zeta potential measurements, XPS, and electron spectroscopy imaging by transmission electron microscopy (ESI/TEM) studies reveal a well-defined core−shell morphology for these particles, whereby the core is polystyrene and the shell comprises the silica sol. After calcination, these nanocomposite particles can form hollow silica capsules. Variation of the initial silica sol and initiator concentration has relatively little effect on the final particle size and silica content of these polystyrene−silica nanocomposite particles, but indicates silica sol incorporation efficiencies up to 72%.

Well-defined μ-[poly(ethylethylene)][poly(ethylene oxide)][poly(γ-methyl-ε-caprolactone)] (μ-EOC) miktoarm star terpolymers were prepared by a combination of two successive living anionic polymerizations and one controlled ring-opening polymerization (ROP). A mid-hydroxyl-functionalized poly(ethylethylene)-block-poly(ethylene oxide) (PEE−PEO) diblock copolymer served as a macroinitiator for the aluminum-mediated ROP of γ-methyl-ε-caprolactone (MCL), leading to a family of μ-EOC triblock copolymers having monomodal molecular weight distributions and controlled PMCL weight fractions. Micelle structures formed in water from μ-EOC containing various lengths of PMCL were examined by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering. Increasing the fraction of hydrophobic PMCL resulted in a transition from spherical to wormlike to approximately spherical micelles. Although the multicompartment cores of the μ-EOC micelles could not be directly resolved by cryo-TEM, small-angle X-ray scattering analysis of a representative PEE−PMCL diblock copolymer showed clear microphase separation, strongly suggesting the existence of multicompartment cores in the μ-EOC micelles. We speculate that the transition of μ-EOC micelles from worms to spheres can be attributed to the connection of the three immiscible blocks at one junction and documented micellar transitions in analogous PMCL−PEO diblock micelles.

Micrometer-sized, monodisperse, "onionlike" multilayered polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA, volume fraction of PS segment in the block copolymer; f PS ≈ 0.5) particles and PS/PS-b-PMMA/PMMA composite particles with different layer thicknesses (D) were successfully prepared by slow release of toluene by evaporation from polymer/toluene droplets dispersed in aqueous media formed using the membrane emulsification method. D is defined as one periodicity consisting of single PS and PMMA layers. The effects of number-average molecular weight (M n of PS-b-PMMA ≈ (7.8-29.0) Â 10 4 g mol -1 ) and volume fraction of PS-b-PMMA (PS/PS-b-PMMA/PMMA = 0/10/0-4.5/1/4.5, v/v/v) on the D of multilayered particles were investigated. The D value increased with an increase in M n to the 2/3 power, in agreement with theory established in polymer blend film systems. PS (M n ≈ (1.1-48.9) Â 10 4 g mol -1 )/ PS-b-PMMA (M n ≈ 29.0 Â 10 4 g mol -1 , f PS ≈ 0.5)/PMMA (M n ≈ (1.3-46.9) Â 10 4 g mol -1 ) composite particles with various volume fractions were also prepared. When the molecular weights of the homopolymers were lower than those of the corresponding polymer segments in the block copolymer, multilayered structures were observed even at a low volume fraction of the block copolymer. On the other hand, when they were higher, microphase and macrophase-separated structures coexisted in all volume fractions. The D of multilayered particles containing low molecular weight homopolymers was proportional to the -1/3 power of the volume fraction of the block copolymer consistent with the theory of the polymer blend film systems, indicating that the D is controllable by proper selection of the experimental conditions. † Part CCCXXIX of the series "Studies on Suspension and Emulsion".

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