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Kōbe-shi, Japan

Kitayama Y.,Kobe University | Moribe H.,Kobe University | Kishida K.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Polymer Chemistry | Year: 2012

Emulsifier-free, organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of methyl methacrylate (MMA) using poly(methacrylic acid) (PMAA)-methyltellanyl (TeMe) (PMAA 30-TeMe) (degree of polymerization of PMAA, 30) was carried out at 60°C with 1000 rpm stirring. The emulsion TERP of MMA did not successfully proceed with maintaining a living manner because of a low chain transfer rate constant relative to propagation rate constant. Moreover, even in the coexistence of (TeBu) 2, the emulsion TERP of MMA also did not proceed with living nature. On the other hand, it in the coexistence of (TeMe) 2 proceeded with good control/livingness. The difference was caused by the different in the solubility in water between (TeBu) 2 and (TeMe) 2. Because (TeBu) 2 is difficult to dissolve in the aqueous phase, it did not work as a catalyst in the aqueous phase, resulting in a homogeneous nucleation. On the other hand, because (TeMe) 2, which is more hydrophilic than (TeBu) 2, works as an efficient catalyst in the aqueous phase, resulting in the self-assembly nucleation. This journal is © The Royal Society of Chemistry 2012.


Kitayama Y.,Kobe University | Kitayama Y.,University of California at Santa Barbara | Kishida K.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2013

Emulsifier-free, organotellurium-mediated living radical emulsion polymerizations (emulsion TERPs) of methyl methacrylate (MMA) and n-butyl methacrylate (BMA) with dimethyl ditelluride were carried out at two different stirring rates (220 rpm and 1000 rpm). In the emulsion TERP of MMA as a hydrophilic monomer, the molecular weight distribution (MWD) controls with both stirring rates were good with high polymerization rate (100% conversion at 1.5 h). On the other hand, in the emulsion TERP of BMA as a hydrophobic monomer, at 220 rpm the polymerization rate was much slow (∼50% conversion at 22 h) and the MWD control was bad, but at 1000 rpm the polymerization was completed within 7 h and MWD control was good. These results suggest that monomer transportation from droplets to polymerizing particles via aqueous medium is important for good MWD control and steady polymerization in the emulsion TERP. © 2012 Wiley Periodicals, Inc.


Kitayama Y.,Kobe University | Kitayama Y.,University of California at Santa Barbara | Tomoeda S.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Macromolecules | Year: 2012

The confined space effect, which was found by the authors, in nitroxide-mediated radical polymerization (NMP) in a microemulsion system (microemulsion NMP) of n-butyl acrylate (BA) was investigated, where the diameter of micelles (monomer droplets) was 5-10 nm and that of poly(BA) (PBA) particles at the completion of the polymerization was ∼60 nm. To clarify the importance of diameter of monomer droplets (d m) in the initial stage of the microemulsion NMP, NMP in a miniemulsion system (miniemulsion NMP) (d m: ∼60 nm) was carried out as a comparative experiment. The miniemulsion NMP proceeded without molecular weight distribution (MWD) control; on the other hand, in the microemulsion NMP the MWD shifted to higher molecular weight with increasing conversion. The livingnesses of PBAs obtained in the initial stages of the miniemulsion and microemulsion NMPs, which were determined by chain extension test, were 0.01% and 64%, respectively. From these results, it is concluded that the confined space effect in the initial stage of the microemulsion NMP effectively operated and resulted in PBA with predetermined molecular weight and good control of MWD even if the diameter of polymerizing particles increased with conversion. © 2012 American Chemical Society.


Yamagami T.,Kobe University | Kitayama Y.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Langmuir | Year: 2014

Micrometer-sized, monodisperse, "mushroom-like" Janus poly(methyl methacrylate)/poly(styrene-2-(2-bromoisobutyryloxy)ethyl methacrylate)-graft- poly(2-(dimethyl amino)ethyl methacrylate) (PMMA/P(S-BIEM)-g-PDM) particles were successfully synthesized by site-selective surface-initiated activator generated by electron transfer for atom transfer radical polymerization in aqueous dispersed systems with spherical PMMA/P(S-BIEM) composite particles having controlled morphologies prepared using the solvent evaporation method. The anisotropic nonspherical shape of the obtained particles was controlled by changing the percentage of the surface area occupied by localized initiation sites (bromine group) at the surface of the PMMA/P(S-BIEM) composite particles with different P(S-BIEM) contents. Grafted PDM layer formed at the surface (contacting with water) of the P(S-BIEM) phase reversibly exhibited the volume phase transition in response to temperature and pH, which gave different nonspherical shapes ("open" or "closed" mushroom-cap). On the basis of such dual stimuli-responsive properties, the nonspherical particles effectively operated as particulate surfactant for Pickering emulsion, resulting in a stable 1-octanol-in-water emulsion at optimum temperature and pH value, and the Pickering emulsion could be easily unstabilized quickly by controlling them. © 2014 American Chemical Society.


Kitayama Y.,Kobe University | Yorizane M.,Kobe University | Minami H.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Macromolecules | Year: 2012

Iodine transfer polymerization (ITP) with CHI 3 as transfer agent and reversible chain transfer catalyzed polymerization (RTCP) with N-iodosuccinimide (NIS) as catalyst of methyl methacrylate (MMA) were successfully applied to aqueous microsuspension systems (respectively, microsuspension ITP and microsuspension RTCP). Both microsuspension ITP and RTCP proceeded smoothly without induction period and with a controlled/living manner. Polydispersity index (PDI, M w/M n) of the microsuspension RTCP was smaller than that of the microsuspension ITP, and it was larger than RTCP in a bulk system (bulk RTCP). The difference seems to be based on that NIS would partly react with water dissolved in the MMA phase, and formed succinimide, which is a low controllable catalyst in comparison with NIS. With decreasing particle (monomer droplet) size, the polymerization rate increased, and a reasonable control was maintained throughout the polymerization based on the segregation effect. © 2012 American Chemical Society.

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