Masayoshi Okubo

Controlled/Living Radical Polymerization in Dispersed Systems

2.6. Microemulsion Polymerization 3778 2.6.1. General Considerations 3778 2.6.2. Microemulsion NMP 3778 2.6.3. Microemulsion ATRP 3778 2.6.4. Microemulsion RAFT Polymerization 3779 2.6.5. ITP in Microemulsion 3779 2.7. Dispersion and Precipitation Polymerizations 3779 2.7.1. General Considerations 3779 2.7.2. NMP 3780 2.7.3. ATRP 3781 2.7.4. RAFT 3782 2.7.5. Dispersion ITP 3782 3. Cross-linking CLRP in Dispersed Systems 3783 3.1. General Considerations 3783 3.2. Cross-linking NMP 3783 3.3. Cross-linking ATRP 3784 3.4. Cross-Linking RAFT Polymerization 3784 3.5. Cross-Linking ITP 3784 4. Particle Morphology 3785 4.1. General Considerations 3785 4.2. Core-Shell Particles 3785 4.3. Hollow Particles 3785 4.4. Multilayered Particles 3786 5. Conclusions and Outlook 3787 6. List of Abbreviations 3788 7. Acknowledgments 3789 8. References 3789

Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic monomer swelling method

Utilizing a new type of monomer swelling method, 6.1 μm-size monodisperse polymer particles were prepared by seeded polymerization. 1.8 μm-size monodisperse polystyrene (PS) seed particles (1.8 μm in size) were prepared by dispersion polymerization in ethanol-water (80/20, v/v) medium in the presence of poly(acrylic acid) as stabilizer with 2,2′-azobisisobutyronitrile as initiator. The PS seed dispersion was mixed with ethanol-water (60/40, v/v) solution dissolving styrene (S) monomer, benzoyl peroxide as initiator, and poly(vinyl alcohol) as stabilizer. By slow, continuous, dropwise addition of water with a micro feeder into the mixture, the PS particles absorbed the many S monomers, which were separated from the medium and swelled from 1.8 μm to 8.4 μm while keeping the monodispersity high. We named this procedure the “dynamic swelling method”. Then, the seeded polymerization of the absorbed S monomer was carried out in the presence of NaNO2 as water-solube inhibitor.

Preparation of micron-size monodisperse polymer microspheres having chloromethyl group

Micron-size monodisperse polymer microspheres having chloromethyl groups thereon were prepared by two-step polymerization process as follows. First, micron-size monodisperse polystyrene particles were prepared by dispersion polymerization with 2,2′-azobisisobutyronitrile as initiator in ethanol-water medium in the presence of poly(acrylic acid) as stabilizer under various conditions. Secondly, in the presence of the 1.9-Μm monodisperse polystyrene particles produced under the optimum conditions, seeded copolymerization for styrene and chloromethyl styrene was carried out. The seeded copolymerization proceeded smoothly without producing new particles, and it was confirmed by x-ray photoelectron spectroscopy that the chloromethyl group existed more at the surface of the produced microsphere than at that of film cast from the benzene solution in which the microspheres were dissolved.

Preparation of micron-size monodisperse polymer particles having highly crosslinked structures and vinyl groups by seeded polymerization of divinylbenzene using the dynamic swelling method

Micron-size monodisperse polystyrene/polydivinylbenzene (PS/PDVB) composite particles having highly crosslinked structures and vinyl groups were prepared as follows. First, 1.9 μm-size monodisperse PS seed particles produced by dispersion polymerization were dispersed in ethanol/water (70/30, w/w) solution which dissolved divinylbenzene (DVB) monomer, benzoyl peroxide as an initiator and poly(vinyl alcohol) as a stabilizer. The PS seed particles were swollen with a large amount of DVB monomers to 4.3 μm in diameter while keeping good monodispersity by the dynamic swelling method, where water was slowly added, continuously, with a micro feeder into the dispersion. And then, the seeded polymerization of the absorbed DVB was carried out.

Effect of particle size on fracture toughness of epoxy resin filled with angular-shaped silica

Abstract The effect of particle size on the fracture behaviour of cured epoxy resin filled with angular-shaped silica was studied. Angular-shaped silica particles were prepared by crushing fused natural raw silica and were classified into six groups with different mean sizes ranging from 2 to 47 μm. Critical stress intensity factor ( K c ) and critical strain energy release rate ( G c ) of the cured epoxy resin filled with these silica particles were measured. Both K c and G c values increased with an increase in particle size of the silica. Scanning electron microscopic observations of crack tips and fractured surfaces showed that the damage zone was formed at the crack tip by particle fracture and by crack diverging. This phenomenon became more pronounced with increase in the particle size. The higher K c and G c values appear to be derived from the dispersion of the stress concentrated at the crack tip due to the crack diverging and from energy absorption due to the formation of a damage zone.

Emulsion polymerization of styrene in a continuous Taylor vortex flow reactor

Abstract A continuous emulsion polymerization of styrene was tried in a Taylor vortex flow reactor which has characteristics of a plug flow reactor. The Taylor vortex flow reactor has the mixing characteristics appropriate for this reaction system. The steady-state conversion, the average molecular weight and the size distribution of latex particles can be controlled by the flow condition as well as by the reaction temperature.

Effect of particle size on the fracture toughness of epoxy resin filled with spherical silica

Abstract The effect of particle size on the fracture behaviour of cured epoxy resin filled with spherical silica particles was studied. Five kinds of spherical silica particles prepared by hydrolysis of silicon tetrachloride having different mean sizes, ranging from 6 to 42 μm, were used. The critical stress intensity factor (Kc) and the critical strain energy release rate (Gc) of the cured epoxy resins filled with the silica particles were measured. Both Kc and Gc values increased with particle size. Scanning electron microscope observation shows that the main crack propagation was hampered by large particles and a damage zone was formed at the main crack tip region in the large particle filled resin due to crack diversion and debonding of particle/matrix interfaces. The higher Kc and Gc values seem to be derived from these phenomena.

Effect of molecular weight on the morphology of polystyrene/poly(methyl methacrylate) composite particles prepared by the solvent evaporation method.

The effect of molecular weight on the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles was investigated. PS/PMMA composite particles with different molecular weights (M*=MwPS+MwPMMA)/2 approximately 2x10(4)-1x10(6) g.mol(-1)) were prepared by the release of toluene (T) from PS/PMMA/T (1/1/24, w/w/w) droplets dispersed in an aqueous solution of polyoxyethylene nonylphenyl ether nonionic surfactant (Emulgen 911). As T evaporated, the spherical droplets phase separated, resulting in snowmanlike composite particles with Janus morphology. The nonspherical shape was closely related to the morphology, which depended on M*. The interfacial tension between the phase-separated PS and PMMA phases increased with an increase in M*, and this would allow the formation of the snowmanlike shape to decrease the interfacial area between the PS and the PMMA phases.

PREPARATION OF MICRON-SIZE MONODISPERSE POLYMER MICROSPHERES HAVING CROSSLINKED STRUCTURES AND VINYL GROUPS

Micron-size monodisperse polymer microspheres having crosslinked structures therein and vinyl groups thereon were prepared by seeded copolymerization of styrene and divinylbenzene with 2,2′-azobisisobutyronitrile as initiator in ethanolwater medium in the presence of 2.1-μm monodisperse polystyrene seed particles produced by dispersion polymerization. The optimum conditions of the seeded copolymerization for producing the microspheres with good monodispersity and colloidal stability were determined.

Control of hollow size of micron-sized monodispersed polymer particles having a hollow structure

Micron-sized monodispersed cross-linked polymer particles having one hollow in the inside were produced by seeded polymerization for the dispersion of (toluene/divinylbenzene)-swollen PS particles prepared utilizing the dynamic swelling method which the authors proposed. In order to control the hollow size, the weight ratio of toluene/PS was changed in the range of 5∼20. The hollow size increased with an increase in the weight ratio. Even if benzene and xylene were used in place of toluene, similar hollow particles were produced, though the hollow size was affected by their solubility in water.