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Star-shaped Polymers (star-shaped + polymer)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2007
Sadahito Aoshima
Abstract Our recent extensive research on Lewis acid catalysts with a weak base for the cationic polymerization of vinyl ethers led to unprecedented living reaction systems: fast living polymerization within 1,3 s; a wide choice of metal halides containing Al, Sn, Fe, Ti, Zr, Hf, Zn, Ga, In, Si, Ge, and Bi; and heterogeneously catalyzed living polymerization with Fe2O3. The use of added bases for the stabilization of the propagating carbocation and the appropriate selection of Lewis acid catalysts were crucial to the success of such new types of living polymerizations. In addition, the base-stabilized living polymerization allowed the quantitative synthesis of star-shaped polymers with a narrow molecular weight distribution via polymer-linking reactions and the precision synthesis and self-assembly of stimuli-responsive block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1801,1813, 2007. [source]

Surface Grafting of PEO-Based Star-Shaped Molecules for Bioanalytical and Biomedical Applications

MACROMOLECULAR BIOSCIENCE, Issue 8 2007
Peter Gasteier
Abstract This article reviews surface grafting of star-shaped PEO. The use of star-shaped polymers is compared to linear PEO chains regarding the layer preparation and the ability of the resulting surfaces to resist protein adsorption. We then focus on the use of end-functionalized, star-shaped, PEO-based prepolymers that are able to form covalent crosslinks and functional polymer networks on the substrate. Examples are given for specific protein adsorption as well as for cell adhesion on such layers by covalent embedding of biofunctional molecules. The possibility of coating biomedically relevant polymer substrates in three-dimensional geometries is discussed and examples are shown for poly(ethylene terephthalate) monofilament constructs. [source]

One-Pot Approach to Synthesize Star-Shaped Polystyrenes via RAFT-Mediated Radical Copolymerization

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2007
Qingchun Liu
Abstract Previously, we have reported a one-pot approach to generate star-shaped polymers by copolymerization of a maleimide inimer or bismaleimide hexane (BMIH) and a large excess of styrene (St) via atom transfer radical polymerization. Herein, we extended this approach towards the synthesis of star polystyrene through reversible addition fragmentation chain-transfer (RAFT)-mediated radical copolymerization of BMIH and an excess of St with cumyl dithiobenzoate (CDB) as a chain-transfer agent (CTA). It was illustrated that the PS arms were grafted from the preformed core, which was formed in situ during the copolymerization of BMIH and St. Therefore, this facile one-pot approach can be performed by applying different type of controlled radical polymerization. However, linear PS still was generated as a byproduct which had been observed previously. [source]

Synthesis of azobenzene-functionalized two-arm, three-arm and four-arm telomers using polyfunctional chain transfer agents

POLYMER INTERNATIONAL, Issue 11 2009
Md Zahangir Alam
Abstract BACKGROUND: Star-shaped polymers are very attractive because of their interesting properties such as reduced viscosity, good solubility, low glass transition temperature and fast response to external stimuli. The incorporation of azobenzene moieties in star-shaped polymers could significantly widen their potential applications in various optical devices. One of the most important properties of the azobenzene chromophore is its reversible trans,cis photoisomerization induced by UV or visible light. Photoisomerization induces conformational changes in azopolymer chains, which in turn lead to macroscopic variations in chemical and physical properties of the surroundings and media. RESULTS: This study reports the synthesis of azobenzene-functionalized two-, three- and four-arm telomers via free radical telomerization using the di-, tri- and tetrafunctional chain transfer agents 1,2- and 1,4-benzenedimethanethiol, trimethylolpropane-tris(2-mercaptoacetate) and pentaerythritol-tetrakis(3-mercaptopropionate), respectively, in the presence of azobisisobutyronitrile. Azotelomers were characterized using gel permeation chromatography and 1H NMR and Fourier transform infrared spectroscopy. Thermal phase transition behaviors were investigated using differential scanning calorimetry and polarized optical microscopy. Azotelomers synthesized in this study showed reversible photoisomerization and a fast generation of birefringence. CONCLUSION: Considering the photoisomerization behavior and birefringence of the two-, three- and four-arm azotelomers, it can be concluded that they could be potential candidates for use in various optical devices. Copyright © 2009 Society of Chemical Industry [source]