Kōbe-shi, Japan
Kōbe-shi, Japan

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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.


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.


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.


Kuroda T.,Kobe University | Tanaka A.,Kobe University | Taniyama T.,Kobe University | Minami H.,Kobe University | And 4 more authors.
Polymer | Year: 2012

Submicrometer-sized, polystyrene (PS) particles with controlled molecular weight distribution (MWD), were successfully obtained directly as powder state by iodine transfer dispersion polymerization (dispersion ITP) and reversible chain transfer catalyzed dispersion polymerization (dispersion RTCP) in supercritical carbon dioxide (scCO 2) for the first time. These dispersion polymerizations proceeded similarly reaching 80% conversion in 21 h. In the dispersion ITP, the number-average molecular weight (M n) nonlinearly increased with the conversion, which were always higher than theoretical values, and the MWD at each conversion was comparatively narrow (M w/M n = 1.5-1.7) throughout polymerization. In the dispersion RTCP, M n also nonlinearly increased with increasing conversion and M w/M n values were in the range of 1.3-1.5, which were lower than those of the dispersion ITP. In chain extension tests in bulk systems, the degrees of livingness of PS prepared by the dispersion ITP and the dispersion RTCP in scCO 2 systems were, respectively, estimated to be 56% and 48%. From these results, while more investigation is necessary, it was concluded that both polymerizations with scCO 2 proceeded in a partly controlled manner. © 2012 Published by Elsevier Ltd.


Yamashita N.,Kobe University | Konishi N.,Kobe University | Tanaka T.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Langmuir | Year: 2012

Micrometer-sized, hemispherical particles were successfully prepared as a result of the cleavage of Janus PMMA/PS composite particles by dispersion into acetone/water (9/1 10/0 v/v) media or a THF/water (8/2 v/v) medium. The spherical composite particles having a Janus structure were prepared by the slow evaporation of toluene from homogeneous PMMA/PS/toluene droplets dispersed in an aqueous medium in advance. It was clarified that the difference in affinity between PMMA and PS phases with respect to the media caused the cleavage of the composite particles. This method is expected to be a novel approach to the preparation of nonspherical polymer particles. © 2012 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.
Polymer Chemistry | Year: 2012

We demonstrated a successful preparation of poly(methyl methacrylate) (PMMA)-b-poly(benzyl methacrylate) (PBzMA) particles in aqueous media by two-step reversible chain transfer catalyzed polymerization (RTCP) with N-iodosuccinimide as a catalyst at 70°C. The polymerization smoothly proceeded, and the number-average molecular weight (M n) increased linearly with conversion, which agreed with the theoretical molecular weight (M n,th). The molecular weight distribution at each conversion was narrow (polydispersity index ≈ 1.4). Approximately 88% PMMA chains became PMMA-b-PBzMA at 64% conversion, which was a relatively high value. This journal is © The Royal Society of Chemistry 2012.


We propose a route to synthesizing ultra-high molecular weight (>106) polystyrene (PS) having a narrow molecular weight distribution by controlled/living radical polymerization. The process is an emulsifier-free, emulsion organotellurium-mediated living radical polymerization (emulsion TERP) using poly(methacrylic acid)-methyltellanyl as a macro-chain transfer agent with a degenerative chain transfer (DT) mechanism. Under the polymerization conditions in which PS particles were formed by a self-assembly nucleation of polymerizing macro-chain transfer agents, very stable PS particles were successfully obtained. The segregation effect in the emulsion polymerization system can suppress the radical termination reaction, resulting in an ultra-high number-average molecular weight (Mn) PS in almost 24 h under 1 atm. The final Mn value was controlled by changing the initial monomer loading (solid contents of styrene), and then PS having a Mn ∼1.2 × 106 with a low polydispersity index (∼1.3) was successfully obtained. © The Royal Society of Chemistry.


Kitayama Y.,Kobe University | Okubo M.,Kobe University | Okubo M.,Smart Spheres Workshop Co.
Polymer Chemistry | Year: 2014

Emulsifier-free, organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of styrene was successfully carried out using poly(dimethylaminoethyl methacrylate) (PDM)-n-butyl tellanyl (TeBu) as control agent and 4,4′-azobis(2-amidinopropane) hydrochloride (V-50) as initiator. Emulsion TERP with inefficient stirring, in which the styrene phase floated as a layer on an aqueous phase, proceeded smoothly and almost finished within 30 h. The molecular weight distribution (MWD) shifted to higher molecular weight with increasing conversion, and Mw/Mn values were relatively small (∼2.0). The MWD control became better with decreasing PDM chain length of the control agent. The inefficient stirring caused better MWD control in the emulsion TERPs using all control agents compared to those with efficient stirring, in which the styrene phase was dispersed as droplets. © 2014 the Partner Organisations.

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