The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Geoffrey W Coates - One of the best experts on this subject based on the ideXlab platform.
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isotactic poly Propylene Oxide a photodegradable polymer with strain hardening properties
Journal of the American Chemical Society, 2020Co-Authors: Bryce M Lipinski, Lilliana S Morris, Meredith N Silberstein, Geoffrey W CoatesAbstract:Leakage and accumulation of highly stable commercial plastics has led to substantial contamination of the environment. Highly isotactic poly(Propylene Oxide) (iPPO) was investigated as a potential ...
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bimetallic chromium catalysts with chain transfer agents a route to isotactic poly Propylene Oxide s with narrow dispersities
Angewandte Chemie, 2018Co-Authors: Lilliana S Morris, Ian M Childers, Geoffrey W CoatesAbstract:Bimetallic chromium catalysts are investigated for the enantioselective polymerization of Propylene Oxide. The catalyst is composed of two salen chromium species linked by an alkyl chain, the length of which significantly impacts the rate of polymerization. While the use of a chloride initiator on the catalyst resulted in bimodal molecular weight distributions, switching to a trifluoroacetate initiating group and adding a diol chain transfer agent afforded polymers of controllable molecular weight with low, unimodal dispersities.
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isospecific chain shuttling polymerization of Propylene Oxide using a bimetallic chromium catalyst a new route to semicrystalline polyols
Journal of the American Chemical Society, 2017Co-Authors: Ian M Childers, Lilliana S Morris, Andrew K Vitek, Peter C B Widger, Syud M Ahmed, Paul M Zimmerman, Geoffrey W CoatesAbstract:Hydroxy-telechelic poly(Propylene Oxide) (PPO) is widely used industrially as a midsegment in polyurethane synthesis. These atactic polymers are produced from racemic Propylene Oxide using chain shuttling agents and double-metal cyanide catalysts. Unlike atactic PPO, isotactic PPO is semicrystalline with a melting temperature of approximately 67 °C. Currently there is no practical route to hydroxy-telechelic isotactic PPO using racemic Propylene Oxide as the monomer. In this paper, hydroxy-telechelic isotactic PPO is synthesized from racemic Propylene Oxide with control of molecular weight using enantioselective and isoselective bimetallic catalysts in conjunction with chain shuttling agents. The discovery of an easily accessible bimetallic chromium catalyst is reported for this transformation. Diol, triol, and polymeric chain shuttling agents are used to give hydroxy-telechelic isotactic PPO of varying functionality and structure. Detailed quantum chemical studies are used to reveal the polymerization me...
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carbonylative polymerization of Propylene Oxide a multicatalytic approach to the synthesis of poly 3 hydroxybutyrate
Journal of the American Chemical Society, 2010Co-Authors: Erin W Dunn, Geoffrey W CoatesAbstract:We report a highly efficient method for the synthesis of poly(3-hydroxybutyrate) by the carbonylative polymerization of Propylene Oxide. The use of compatible epOxide carbonylation and lactone polymerization catalysts allows for a one-pot reaction that eliminates the need to isolate and purify the toxic β-butyrolactone intermediate.
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two dimensional double metal cyanide complexes highly active catalysts for the homopolymerization of Propylene Oxide and copolymerization of Propylene Oxide and carbon diOxide
Dalton Transactions, 2006Co-Authors: Nicholas J Robertson, Zengquan Qin, Gregory C Dallinger, Emil Lobkovsky, Stephen Lee, Geoffrey W CoatesAbstract:The synthesis of two-dimensional double metal cyanide complexes of the formula Co(H2O)2[M(CN)4]·4H2O (M = Ni, Pd or Pt) and the X-ray crystal structure of Co(H2O)2[Pd(CN)4]·4H2O are presented. The anhydrous forms of these complexes were found to be effective catalyst precursors for the homopolymerization of Propylene Oxide as well as the random copolymerization of Propylene Oxide and carbon diOxide to produce poly(Propylene Oxide-co-Propylene carbonate) with no Propylene carbonate byproduct. A detailed copolymer microstructure is proposed.
Shen Zhiquan - One of the best experts on this subject based on the ideXlab platform.
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copolymerization of Propylene Oxide and co 2 catalyzed by a rare earth borohydride diethylzinc glycerine ternary system copolymerization of Propylene Oxide and co 2 catalyzed by a rare earth borohydride diethylzinc glycerine ternary system
Chinese Journal of Catalysis, 2010Co-Authors: Liu Guangxuan, Li Cong, Ni Xufeng, Jiang Liming, Shen ZhiquanAbstract:A ternary catalytic system composed of rare earth borohydrides, diethylzinc, and glycerine has been developed and found to be effective for the copolymerization of Propylene Oxide (PO) with carbon diOxide. The effect of catalyst composition and reaction conditions on the copolymerization was examined through orthogonal experiments. With Y(BH4)(3)center dot 3THF-ZnEt2-glycerine molar ratio of 3:60:20, the highest turnover frequency (TOF) of 4 908 g/(mol.h) was achieved at 80 degrees C and 3.0 MPa of CO2 using 1,2-dimethoxyethane as solvent. The poly(Propylene carbonate) had a carbonate unit content of 95.7% and number-average molecular mass of 6.97 x 10(4).
Paschalis Alexandridis - One of the best experts on this subject based on the ideXlab platform.
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poly ethylene Oxide poly Propylene Oxide block copolymer surfactants
Current Opinion in Colloid and Interface Science, 1997Co-Authors: Paschalis AlexandridisAbstract:Block copolymers consisting of poly(ethylene Oxide) (PEO) and poly(Propylene Oxide) (PPO) can self-assemble in water and water/oil mixtures (where water is a selective solvent for PEO and oil a selective solvent for PPO) to form thermodynamically stable spherical micelles as well as an array of lyotropic liquid crystalline mesophases of varying morphology. Significant advances have been made over the past year on the identification of different morphologies, the delineation of the composition-temperature ranges where they occur, and the structural characterization of the morphologies using primarily small angle scattering techniques. Important new findings on the copolymer micellization in water as affected by cosolutes, and on the time-dependency of the surface activity have also been reported.
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microviscosity in pluronic and tetronic poly ethylene Oxide poly Propylene Oxide block copolymer micelles
Langmuir, 1995Co-Authors: Thierry Nivaggioli, Belinda Tsao, Paschalis Alexandridis, Alan T HattonAbstract:The micellar microviscosity afforded by Pluronic and Tetronic poly(ethylene Oxide)-poly(Propylene Oxide) block copolymer aqueous solutions has been investigated by fluorescence and NMR spectroscopy. Comparison is made with bulk poly(Propylene Oxide) (PPO) samples of different molecular weights. The microviscosity in Pluronic PEO-PPO-PEO copolymer micelles is much larger than that observed in conventional surfactant micelles and depends strongly on the size of the hydrophobic PPO block: the larger this block, the higher the viscosity. Above the critical micellar temperature (CMT), as temperature increases, the microviscosity decreases. However, this decrease is not as important as that observed in bulk PPO. Hence, the relative microviscosity, defined as the ratio of the two observed phenomena, increases. This suggests structural transformation of the micelles resulting in a core becoming more and more compact as temperature increases. Such results have been confirmed by NMR studies that showed broadening of the PPO peak and relatively constant spin-lattice relaxation time, T 1 , with increasing temperature while the PEO signal remained relatively sharp with an exponential increase in T 1 . In addition, solubilization of benzene in Pluronic copolymer micelles as detected by NMR indicated that benzene partitions preferentially in the core of the micelle constituted mainly of PPO
Stephane Carlotti - One of the best experts on this subject based on the ideXlab platform.
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activated anionic ring opening polymerization for the synthesis of reversibly cross linkable poly Propylene Oxide based on furan maleimide chemistry
Polymer Chemistry, 2016Co-Authors: Kevin Roos, Stephane Carlotti, Elena Dolci, Sylvain CaillolAbstract:The synthesis of cross-linkable random copolyethers of Propylene Oxide (PO) and furfuryl glycidyl ether (FGE) is first discussed. The anionic ring-opening polymerization and monomer activation methodology, based on the combination of tetraoctylammonium bromide and triisobutylaluminum, is used to perform the controlled synthesis of poly(Propylene Oxide-co-furfuryl glycidyl ether) copolymers with various compositions 95/5, 90/10, 75/25, 50/50, and 25/75 (PO/FGE mol%) and keeping the furfuryl moieties active. Copolymers with molar masses around 10000 g mol−1 were obtained in short times. Subsequently, the furfuryl moieties were reacted with aromatic and aliphatic maleimide-based cross-linkers to perform Diels–Alder (DA) “click” reactions. Three-dimensional networks were obtained and their swelling ratio and insoluble fraction were determined. Glass transition temperature and retro-Diels–Alder (rDA) transition in the network were determined by differential scanning calorimetry analyses. Gel properties vary with the furan group amount in the initial copolymer and the cross-linker structure. The network disassembly at 110 °C was monitored by 1H NMR and quantitatively recorded by the re-appearance of the copolymer signals due to the rDA reaction. The solubility study showed that the gel was able to reform at 20 °C leading to reversible cross-linked polyethers.
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Grignard-based anionic ring-opening polymerization of Propylene Oxide activated by triisobutylaluminum
European Polymer Journal, 2015Co-Authors: Roos Kevin, Stephane CarlottiAbstract:Better known as alkylating agents, Grignard reagents are investigated as deprotonating agents of an alcohol to generate magnesium alkOxides for the initiation and propagation of the anionic ring-opening polymerization of Propylene Oxide. By using an excess of triisobutylaluminum, this magnesium-aluminum system enables a full conversion polymerization in a few hours yielding controlled poly(Propylene Oxide) up to 10000 g/mol with relatively low dispersity. Characterizations by NMR and MALDI-ToF-mass spectrometry allowed the determination of the chain-ends and therefore the associated initiation mechanisms. This study revealed that Propylene Oxide can be polymerized in presence of a magnesium-based counter-ion. Concomitant initiations by alkOxide, halide and hydride are discussed.
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controlled anionic homo and copolymerization of ethylene Oxide and Propylene Oxide by monomer activation
Macromolecules, 2007Co-Authors: Virginie Rejsek, Cyrille Billouard, Philippe Desbois, Alain Deffieux, David Sauvanier, Stephane CarlottiAbstract:The anionic polymerization of ethylene Oxide initiated by alkali metal-based initiators suffers from low polymerization rates even in polar media. We found that the addition of triisobutylaluminum to initiators like alkali metal alkOxides or tetraalkylammonium salts strongly enhances the ethylene Oxide polymerization rate, while keeping its living character. At ratio [i-Bu3Al]/[initiator] = 1.5, the controlled synthesis of poly(ethylene Oxide) of relatively high molar masses is achieved in short time at room temperature in dichloromethane or toluene. Beside the formation of an aluminate 1:1 complex involving i-Bu3Al and the initiator, a second complex between the trialkylaluminum and the oxirane is formed, which strongly increases the reactivity of the epOxide monomer. Gradient di- and triblock ethylene Oxide/Propylene Oxide copolymers of high molar mass are readily prepared with this system.
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controlled high speed anionic polymerization of Propylene Oxide initiated by alkali metal alkOxide trialkylaluminum systems
Macromolecules, 2004Co-Authors: Cyrille Billouard, Stephane Carlotti, Philippe Desbois, Alain DeffieuxAbstract:The anionic polymerization of Propylene Oxide initiated by alkali metal alkOxide suffers from several drawbacks such as a slow polymerization rate in nonpolar solvents and an important chain transfer reaction to monomer. We found that the addition of trialkylaluminum to the alkali metal alkOxide/Propylene Oxide system in hydrocarbon media strongly enhances the polymerization rate and strongly reduces the transfer reactions, thus allowing the controlled synthesis of poly(Propylene Oxide) with relatively high molar masses (up to 20 000 g/mol). At constant monomer and alkali metal alkOxide concentrations the polymerization rate increases with increasing trialkylaluminum concentration. Kinetic data and 1H NMR studies indicate that the trialkylaluminum derivative is involved in the formation of two distinct complexes, one with the alkali metal alkOxide and another with the PO monomer. The strong electron-withdrawing on PO α-carbons associated with AlR3 complexation makes the monomer much more susceptible to ri...
Liu Guangxuan - One of the best experts on this subject based on the ideXlab platform.
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copolymerization of Propylene Oxide and co 2 catalyzed by a rare earth borohydride diethylzinc glycerine ternary system copolymerization of Propylene Oxide and co 2 catalyzed by a rare earth borohydride diethylzinc glycerine ternary system
Chinese Journal of Catalysis, 2010Co-Authors: Liu Guangxuan, Li Cong, Ni Xufeng, Jiang Liming, Shen ZhiquanAbstract:A ternary catalytic system composed of rare earth borohydrides, diethylzinc, and glycerine has been developed and found to be effective for the copolymerization of Propylene Oxide (PO) with carbon diOxide. The effect of catalyst composition and reaction conditions on the copolymerization was examined through orthogonal experiments. With Y(BH4)(3)center dot 3THF-ZnEt2-glycerine molar ratio of 3:60:20, the highest turnover frequency (TOF) of 4 908 g/(mol.h) was achieved at 80 degrees C and 3.0 MPa of CO2 using 1,2-dimethoxyethane as solvent. The poly(Propylene carbonate) had a carbonate unit content of 95.7% and number-average molecular mass of 6.97 x 10(4).
