Search results for "Chain transfer"
showing 10 items of 85 documents
How Many Phosphoric Acid Units Are Required to Ensure Uniform Occlusion of Sterically Stabilized Nanoparticles within Calcite?
2019
Polymerization-induced self-assembly (PISA) mediated by reversible addition-fragmentation chain transfer (RAFT) polymerization offers a platform technology for the efficient and versatile synthesis of well-defined sterically stabilized block copolymer nanoparticles. Herein we synthesize a series of such nanoparticles with tunable anionic charge density within the stabilizer chains, which are prepared via statistical copolymerization of anionic 2-(phosphonooxy)ethyl methacrylate (P) with non-ionic glycerol monomethacrylate (G). Systematic variation of the P/G molar ratio enables elucidation of the minimum number of phosphate groups per copolymer chain required to promote nanoparticle occlusi…
Double Thermoresponsive Block Copolymers Featuring a Biotin End Group
2010
A poly(oligo(ethylene glycol) monomethyl ether methacrylate)-block-poly(N-isopropyl methacrylamide) (POEGMA-b-PNIPMAM) block copolymer with a biotin end group on the PNIPMAM block as a biotarget was synthesized as a model system for temperature-controlled polymer immobilization. The synthesis was based on RAFT polymerization followed by postpolymerization modification of an activated ester precursor block and an exchange of the dithioester end group within one step. NMR, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and turbidimetry measurements were performed to investigate the stimulus-responsive properties. The double thermoresponsive POEGMA-b-PNIPMAM with biot…
Controlled synthesis of poly(acetone oxime acrylate) as a new reactive polymer: Stimuli-responsive reactive copolymers
2007
Abstract Acetone oxime acrylate has been synthesized as a new active ester monomer. Free radical polymerization yielded a reactive polymer soluble in various organic solvents, such as chloroform, dioxane, DMSO, acetone, methanol, dichloromethane, DMF, and ethanol. Controlled radical polymerization of acetone oxime acrylate was successfully conducted using the RAFT, NMP and Iniferter method. Partly polymer analogous reaction with N-isopropylamine resulted in the reactive copolymer poly(N-isopropylacrylamide-co-acetone oxime acrylate), which featured a lower critical solution temperature (LCST) of 61 °C in water. Further, the reactivity of the copolymer was exemplary proven by complete reacti…
Stabilizing nanostructured lithium insertion materials via organic hybridization: A step forward towards high-power batteries
2014
Abstract Herein, we present the electrochemical characterization of carbon-coated TiO 2 nanorods, obtained by carbonizing RAFT (reversible addition fragmentation chain transfer) polymerization derived block copolymers anchored on anatase TiO 2 nanorods. These carbon-coated TiO 2 nanorods show an improved electrochemical performance in terms of first cycle reversibility, specific capacity, cycling stability, and high rate capability. More importantly, however, the structural disordering observed in the uncoated TiO 2 nanorods by means of galvanostatic and potentiodynamic cycling as well as ex situ XRD analysis, does not occur for the carbon-coated material. Preventing this structural disorde…
Controlled radical polymerization of styrene in miniemulsion polymerization using reversible addition fragmentation chain transfer
2003
Abstract Miniemulsion polymerizations of styrene in the presence of two reversible addition–fragmentation chain-transfer (RAFT) agents were studied. The rates were significantly retarded by the presence of a RAFT agents S -(thiobenzoyl)thioglycolic acid, 1 , or dithiobenzoic acid 1-phenylethyl ester, 2 . Control in miniemulsion polymerization is not as good as for bulk polymerizations. The miniemulsions could also be stabilized against Ostwald ripening by a polymer terminated by a dithiobenzoic moiety. In this case, the polymerization was not controlled because of the generation of renucleated particles. To cite this article: I. Uzulina et al., C. R. Chimie 6 (2003).
Transition Metal Catalyzed Olefin, Cycloolefin, and Styrene Polymerization
2013
The sections in this article are History and Trends Polymerization Processes Supported Catalysts and Morphology Control Polymerization Mechanisms and Stereoselectivity History and Principles of Metallocene Catalysis Regio- and Stereoselective Polymerization of α-Olefins Polymerization of Cyclic Olefins, Cyclopolymerization, and Stereoselective Polymerization of Styrene Late Transition Metal Catalysts Transition Metal Catalyzed Copolymerization Acknowledgements
Conducting Polymer with Orthogonal Catechol and Disulfide Anchor Groups for the Assembly of Inorganic Nanostructures
2017
To combine several inorganic components with organic material in a controlled special and permanent manner still remains a difficult issue. Two specifically functionalized block copolymers were synthesized separately and combined in a second step. A heterofunctional poly(ethylene glycol) (PEG) block copolymer bearing a single amino unit, a short PEG spacer, and multiple catechol functionalities was obtained via anionic ring-opening polymerization (AROP). Using the reversible addition–fragmentation chain transfer (RAFT) radical polymerization technique, a semiconducting block copolymer with carbazole side groups was obtained. The second polyacrylate block contained reactive ester groups and …
Metal-free polymerization of phenylsilane: tris(pentafluorophenyl)borane-catalyzed synthesis of branched polysilanes at elevated temperatures.
2013
The strong organoborane Lewis acid B(C6F5)3 catalyzes the polymerization of phenylsilane at elevated temperatures forming benzene and SiH4 as side-products. The resulting polymer is a branched polysilane with an irregular substitution pattern, as revealed by 2D NMR spectroscopy. Having explored the mechanism of this novel metal-free polymerization by computational chemistry methods at the DFT level, we have suggested that unusual cationic active species, namely monomer-stabilized silyl cations, propagate the polymerization. Hydride abstraction of SiH3 moiety by the catalyst in the initiation step was found to be kinetically preferred by around 9 kcal mol(-1) over activation by coordination …
Polymerisation von äthylenoxid mit dem kaliumalkoholat von 4-benzolazo-benzylalkohol. II. Die quantitative bestimmung einer übertragungsreaktion
1966
Die Untersuchung von Polyathylenoxiden, die mit dem Kaliumalkoholat von 4-Benzolazo-benzylalkohol und Athylenoxid erhalten wurden, ergab, das nicht jedes Polyathylenoxidmolekul eine Endgruppc aus dein Polymerisationsstarter enthielt. Die vermutete Ubertragungsreaktion mit Wasserspuren wurde folgendermasen nachgewiesen und quantative bestimint. Eine quantitative Umsetzung der Polyathylenoxide mit(4-Benzolazobenzoesa-)anhydrid gab mittels colorimetrischer Messungen den Gehalt an HO-Endgruppen. Der Vergleich des Gehaltes an Endgruppen aus dem Starter mit dem HO-Endgruppengehalt zeigte ein starkes Uberwiegen der HO-Endgruppen. Die Zahlenmittel der Molekulargewichte (Mn) von Polyathylenoxidfrakt…
From Defined Reactive Diblock Copolymers to Functional HPMA-Based Self-Assembled Nanoaggregates
2008
This paper describes the synthesis of functional amphiphilic poly( N-(2-hydroxypropyl) methacrylamide)-block-poly(lauryl methacrylate) copolymers by RAFT polymerization via the intermediate step of activated ester block copolymers (pentafluoro-phenyl methacrylate). Block copolymers with molecular weights from 12000-28000 g/mol and PDIs of about 1.2 have been obtained. The amphiphilic diblock copolymers form stable super structures (nanoaggregates) by self-organization in aqueous solution. The diameters of these particles are between 100 and 200 nm and depend directly on the molecular weight of the block copolymer. Furthermore, we investigated the impact of these nanoaggregates on cell viabi…