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Abraham, Sinoj,Choi, Jae Ho,Ha, Chang-Sik,Kim, Il Wiley Subscription Services, Inc., A Wiley Company 2007 Journal of polymer science Part A, Polymer chemist Vol.45 No.23
<P>The synthesis of new octafunctional alkoxyamine initiators for nitroxide-mediated radical polymerization (NMRP), by the derivatization of resorcinarene with nitroxide free radicals viz TEMPO and a freshly prepared phosphonylated nitroxide, is described. The efficiency of these initiators toward the controlled radical polymerization of styrene and tert-butyl acrylate is investigated in detail. Linear analogues of these multifunctional initiators were also prepared to compare and evaluate their initiation efficiency. The favorable conditions for polymerization were optimized by varying the concentration of initiators and free nitroxides, reaction conditions, etc., to obtain well-defined star polymers. Star polystyrene thus obtained were further used as macro-initiator for the block copolymerization with tert-butyl acrylate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5559–5572, 2007</P> <B>Graphic Abstract</B> <P>The synthesis of new octafunctional alkoxyamine initiators for nitroxide-mediated radical polymerization (NMRP), by the derivatization of resorcinarene with nitroxide free radicals viz TEMPO and a freshly prepared phosphonylated nitroxide, is described. The efficiency of these initiators towards the controlled radical polymerization of styrene and tert-butyl acrylate is investigated in detail. Linear analogues were also prepared to compare the initiation efficiency. The favorable conditions for polymerization were optimized by varying reaction parameters, to obtain well-defined star polymers. Star polystyrene thus obtained were further used as macroinitiator for the block copolymerization with tert-butyl acrylate. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]</P><P> <img src='wiley_img/0887624X-2007-45-23-POLA22302-gra001.gif' alt='wiley_img/0887624X-2007-45-23-POLA22302-gra001'> </P>
Abraham, Sinoj,Ha, Chang-Sik,Kim, Il Wiley Subscription Services, Inc., A Wiley Company 2005 Journal of polymer science Part A, Polymer chemist Vol.43 No.24
<P>A series of poly(styrene-block-tert-butyl acrylate) heteroatom star block copolymers having various block lengths were prepared by atom transfer radical polymerization (ATRP), using an “as synthesized” cynurate modified trifunctional initiator. The structure of the star polymers was confirmed by the characterization of the individual arms resulting from hydrolysis. Amphiphilic poly(styrene-block-acrylic acid) star copolymers were further synthesized by hydrolyzing PtBA blocks using anhydrous trifluoroacetic acid. The characterization data are reported from analyses using gel permeation chromatography, infrared, <SUP>1</SUP>H and <SUP>13</SUP>C NMR spectroscopies. The stable micelle solution was prepared by dialyzing the solution of these polymers in N,N-dimethylformamide against deionized water. The temperature-induced associating behavior of these amphiphilic star polymers were studied using dynamic laser light scattering spectroscopy. The hydrodynamic diameter of both micelles and unassociated chains were obtained in the same solution using light scattering cumulant's calculation method. The homogeneity and the size distribution of the micelle population in the solution were determined using centrifuge/sedimentation particle size distribution analyzer. Field emission scanning electron microscope was used to visualize the size of the micelles formed and the micellar aggregates. The influence of the temperature on the viscosity of the micelle solution was studied using an Ubbelohde viscometer. Thermodynamics of micellization of these block copolymers were also investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6367–6378, 2005</P> <B>Graphic Abstract</B> <P>A series of poly(styrene-block-tert-butyl acrylate) heteroatom star block copolymers having various block lengths were prepared by atom transfer radical polymerization (ATRP), using an “as synthesized” cynurate modified trifunctional initiator. The block copolymers were chemically modified so as to accomplish hydrophilic nature. The associating behavior of these copolymers was investigated by light scattering, viscometry, and field emission SEM. The determination of cmtvalues at different concentrations enabled to study the enthalpy of micellization and it seems to be negative, favoring the micellization phenomenon. The combination of the experimental techniques used herein made investigations of the association parameters, the thermodynamic properties, and the micellar structure of the amphiphilic PS-b-PAA star block copolymers feasible.</P> <img src='wiley_img/0887624X-2005-43-24-POLA21082-gra001.gif' alt='wiley_img/0887624X-2005-43-24-POLA21082-gra001'>
Abraham, Sinoj,Jeong, Eun Ho,Arakawa, Takahiro,Shoji, Shuichi,Kim, Kyung Chun,Kim, Il,Go, Jeung Sang Royal Society of Chemistry 2006 Lab on a chip Vol.6 No.6
<P>In this article, the development of a novel technique to fabricate spherical polymeric microcapsules by utilizing microfluidic technology is presented. Atom transfer radical polymerization (ATRP) was employed to synthesize well-defined amphiphilic block copolymers. An organic polymer solution was constrained to adopt the spherical droplets in a continuous water phase at a T-junction microchannel, and the generation of the droplets was studied quantitatively. The flow conditions of two immiscible solutions were adjusted for the successful generation of the polymer droplets. The morphology of the microcapsules was examined. The efficiency of these polymer microcapsules as containers for the storage and controlled release of loaded molecules was evaluated by encapsulating the microcapsules with Congo-red dye and investigating the release performance using temperature controlled UV-VIS spectroscopy.</P> <P>Graphic Abstract</P><P>The priority of this work is the innovative conjunction of well-defined amphiphilic block copolymers and stable microfluidics to develop the functional spherical microcapsule with quantitative evaluation of its drug release performance, potentially aiming at mass-production. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b518006f'> </P>
Abraham, Sinoj,Choi, Jae-Ho,Lee, Jin-Kyu,Ha, Chang-Sik,Kim, Il The Polymer Society of Korea 2007 Macromolecular Research Vol.15 No.4
An octa-functional alkoxyamine initiator, with the 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) free radical, was synthesized based on resorcinarene, with its efficiency to initiate the nitroxide-mediated free radical copolymerization of styrene and methyl methacrylate (MMA) described. A difunctional analogue of this initiator was also synthesized, using resorcinol as the core molecule. The structures of the resulting initiators were confirmed by homolysis studies based on electron spin resonance spectroscopy and molecular modeling. The polymerization behavior and characteristics of the polymers obtained using these two initiators were also compared. Well-defined star-shaped and linear random copolymers, with low polydispersities and controlled molecular weights, were prepared. The efficiencies of these initiators towards copolymerization, as well as the parameters permitting the formation of well-defined polymers, were also investigated. The reactivity ratios were $r_a=0.42(a=styrene)\;and\;r_b=0.33(b=MMA)$ for the octa-functional initiator system and $r_a=0.45\;and\;r_b=0.39$ for the difunctional initiator system.
Abraham, Sinoj,Ha, Chang-Sik,Kim, Il WILEY-VCH Verlag 2006 Macromolecular Rapid Communications Vol.27 No.16
<P>Summary: The synthesis of a novel series of multi-nuclear macroligated pyridylimine based palladium(II) complexes conjugated to a synthetic star polymer core has been well-described. Star shaped polystyrene with a finite number of arms were prepared by atom transfer radical polymerization (ATRP) and the chain ends were chemically modified in order to introduce the desired end functionality. Utilizing this polymer as organic supports for pyridylimine-based ligands, palladium(II) complexes were synthesized. On activating with methylaluminoxane (MAO), this complex showed substantially high activity towards ethylene oligomerization, producing C<SUB>4</SUB> and C<SUB>6</SUB> compositions as major products. The plausible mechanistic insight concerning the process of ethylene oligomerization is also broached.</P><P> <img src='wiley_img/10221336-2006-27-16-MARC200600244-gra001.gif' alt='wiley_img/10221336-2006-27-16-MARC200600244-gra001'> Graphic An example of trinuclear pyridylimine based palladium(II) complex having a functionalized star polystyrene core. </P>