The Experts below are selected from a list of 3609 Experts worldwide ranked by ideXlab platform
Wenxin Wang - One of the best experts on this subject based on the ideXlab platform.
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intramolecular cyclization dominating Homopolymerization of multivinyl monomers toward single chain cyclized knotted polymeric nanoparticles
Macromolecules, 2015Co-Authors: Yongsheng Gao, Tianyu Zhao, Dezhong Zhou, Udo Greiser, Xuan Wei, Sean Mcmahon, Jonathan Okeeffe Ahern, Wei Wang, Brian J Rodriguez, Wenxin WangAbstract:Polymerization of multifunctional monomers could produce polymers with different functionalities and novel macromolecular architectures. However, the ability to control the Homopolymerization of multivinyl monomers (MVMs) has always been a challenge. Here we demonstrate that the Homopolymerization of acrylate based MVMs can be kinetically controlled via Cu0-mediated controlled/living radical polymerization in the presence of additional CuII, which enables the efficient promotion of intramolecular cyclization and suppression of intermolecular cross-linking. The gelation is effectively delayed over ca. 40% monomer conversion in the concentrated polymerization system ([M] = 40.9 wt %), which is far higher than the Flory–Stockmayer theory predicts. Moreover, closer inspection of the synthesized polymers reveals that single-chain cyclized/knotted polymeric nanoparticles (SCKNPs) are formed due to the nature of one-pot in situ intramolecular reaction and self-cyclization of the propagating polymer chains. This ...
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water soluble hyperbranched polymers from controlled radical Homopolymerization of peg diacrylate
RSC Advances, 2015Co-Authors: Tianyu Zhao, Hong Zhang, Dezhong Zhou, Yongsheng Gao, Yixiao Dong, Udo Greiser, Hongyun Tai, Wenxin WangAbstract:A series of water soluble PEG based hyperbranched polymers were successfully synthesized by Homopolymerization of poly(ethylene glycol) diacrylate (PEGDA) (Mn = 575 and 700 g mol−1 respectively) via vinyl oligomer combination. The Homopolymerization of diacrylate macromers underwent a slow vinyl propagation combined with a polycondensation by coupling of reactive oligomers. At a high initiator-to-monomer ratio (e.g. 1 : 2), high monomer conversions up to 96% were achieved in concentrated reaction conditions (60% w/v) without gelation. The hyperbranched polymers obtained from Homopolymerization of PEGDA575 show concentration-dependent thermoresponsive properties in aqueous solutions.
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controlled Homopolymerization of multi vinyl monomers dendritic polymers synthesized via an optimized atra reaction
Chemical Communications, 2013Co-Authors: Yu Zheng, Tianyu Zhao, Ben Newland, Julien Poly, Wenxin WangAbstract:In this study, we have managed to find the optimal ATRA system that can obtain the highest mono-adduct yields with the purpose of minimizing the chain growth of divinyl monomers. The most highly hyperbranched polymers have been synthesized by the Homopolymerization of multi-vinyl monomers via ATRA reaction.
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single cyclized molecule structures from raft Homopolymerization of multi vinyl monomers
Chemical Communications, 2012Co-Authors: Yu Zheng, Hongyun Tai, Ben Newland, Abhay Pandit, Wenxin WangAbstract:We explore a kinetically controlled strategy to suppress the gelation in the Homopolymerization of multi-vinyl monomers (MVMs) viaRAFT polymerization. We report the generation of 3D single cyclized polymer structures from the RAFT process, which significantly contradicts the classic F–S theory. This approach enables synthesis of a new generation of nanosize macromolecular architectures.
Zhiqiang Fan - One of the best experts on this subject based on the ideXlab platform.
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kinetics and mechanism of metallocene catalyzed olefin polymerization comparison of ethylene propylene Homopolymerizations and their copolymerization
Journal of Polymer Science Part A, 2017Co-Authors: Yintian Guo, Zhen Zhang, Wenqi Guo, Akbar Khan, Zhiqiang FanAbstract:A series of ethylene, propylene Homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac-Et(Ind)2ZrCl2/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2-thiophenecarbonyl chloride to label a 2-thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene Homopolymerization) and copolymer composition with time were also studied. [C*]/[Zr] strongly depended on type of monomer, with the propylene Homopolymerization system presented much lower [C*]/[Zr] (ca. 25%) than the ethylene Homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C*]/[Zr] of ethylene Homopolymerization (ca. 70%). The chain propagation rate constant (kp) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the Homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene Homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 867–875
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effects of ethylene as comonomer on the active center distribution of 1 hexene polymerization with mgcl2 supported ziegler natta catalysts
Journal of Molecular Catalysis A-chemical, 2011Co-Authors: Zhiqiang Fan, Letian Zhang, Shengjie XiaAbstract:Abstract 1-Hexene Homopolymerization and 1-hexene–ethylene copolymerization with TiCl4/MgCl2–Al(C2H5)3 catalyst were compared to investigate the effect of ethylene on the distribution of active centers. The polymerizations were quenched with cinnamoyl chloride, and the number of active centers ([C*]/[Ti]) was determined by measuring the cinnamoyl group labeled on the propagation chains. Both polymer samples were fractionated into 9–10 fractions according to molecular weight, and [C*]/[Ti] in each fraction was also determined. Adding small amount of ethylene in 1-hexene polymerization markedly increased the number of active centers that produce low molecular weight polymer. This phenomenon agrees with the mechanism suggesting the presence of Ti−CH(CH3)(CH2)3CH3 type dormant sites and their activation by ethylene. The kp value of the newly emerging active centers in the copolymerization system is much lower than that of the Homopolymerization system. In the copolymerization system, the active centers producing polymer chains of the second highest molecular weight and isotacticity show the highest kp value, while those producing polymer of the highest molecular weight and isotacticity show only the second highest kp. On the other hand, the active centers producing polymer with lower–middle chain length show the lowest ethylene incorporation rate. These results disclose differences of catalytic properties between the multiple active center types and correlations between their different kinetic parameters, which may lead to new understanding of the active centers and polymerization mechanism.
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regulation of morphology and mechanical properties of polypropylene poly ethylene co propylene in reactor alloys by multi stage sequential polymerization
Polymer, 2007Co-Authors: Qi Dong, Zhiqiang Fan, Xiaofeng WangAbstract:Abstract A series of polypropylene/poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys were synthesized by the Homopolymerization of propylene in the first stage, after that it switches to gas-phase ethylene–propylene copolymerization and gas-phase Homopolymerization of propylene in a circular mode. The alloys were characterized by FTIR, DSC, PLM, TEM and SEM. Changing switch frequency had hardly any influence on the EPR content of the PP/EPR in-reactor alloys. However, as the switch frequency increased, the catalyst efficiency evidently increased. Measurement of mechanical properties shows that increasing the switch frequency has a positive effect on both the impact strength and flexural modulus. Although the content of EPR was almost similar to each other, as the switch frequency increased, the size of EPR phase decreases and the size distribution in the PP matrix trend to be more uniform that forms strong interfacial adhesion between PP phase and EPR phase. The simultaneous improvement of both impact strength and flexural modulus of the alloy can be mainly attributed to changes in its phase morphology as a result of fast circulation between Homopolymerization and copolymerization.
Robert Jerome - One of the best experts on this subject based on the ideXlab platform.
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living anionic Homopolymerization and block copolymerization of dimethylamino ethyl methacrylate
Macromolecules, 1997Co-Authors: Serge Creutz, Philippe Teyssie, Robert JeromeAbstract:Anionic polymerization of (dimethylamino)ethyl methacrylate (DMAEMA) has been investigated in THF at −78 °C. The presence of lithium chloride has been shown to be desirable in order to afford a narrow molecular weight distribution as well as a good agreement between theoretical and observed molecular weight. The living character of the polymerization has been demonstrated. Thus the synthesis of block copolymers, some of them unattainable by GTP, has been carried out successfully. Finally, the anionic polymerization of mixtures of tert-butyl methacrylate (tBMA) and DMAEMA has been considered and their relative reactivity ratio estimated. The easy quaternization of (dimethylamino)ethyl methacrylate affords amphiphilic water-soluble copolymers displaying interesting characteristics as polymeric dispersants and surfactants.
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living anionic Homopolymerization and block copolymerization of dimethylamino ethyl methacrylate
Macromolecules, 1997Co-Authors: Serge Creutz, Philippe Teyssie, Robert JeromeAbstract:Anionic polymerization of (dimethylamino)ethyl methacrylate (DMAEMA) has been investigated in THF at −78 °C. The presence of lithium chloride has been shown to be desirable in order to afford a narrow molecular weight distribution as well as a good agreement between theoretical and observed molecular weight. The living character of the polymerization has been demonstrated. Thus the synthesis of block copolymers, some of them unattainable by GTP, has been carried out successfully. Finally, the anionic polymerization of mixtures of tert-butyl methacrylate (tBMA) and DMAEMA has been considered and their relative reactivity ratio estimated. The easy quaternization of (dimethylamino)ethyl methacrylate affords amphiphilic water-soluble copolymers displaying interesting characteristics as polymeric dispersants and surfactants.
Bernadette Charleux - One of the best experts on this subject based on the ideXlab platform.
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raft mediated one pot aqueous emulsion polymerization of methyl methacrylate in presence of poly methacrylic acid co poly ethylene oxide methacrylate trithiocarbonate macromolecular chain transfer agent
Polymer, 2013Co-Authors: Wenjing Zhang, Franck Dagosto, Pierreyves Dugas, Jutta Rieger, Bernadette CharleuxAbstract:Abstract The polymerization-induced self-assembly of amphiphilic block copolymers in water was performed following a reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization mechanism in emulsion. Poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate), P(MAA-co-PEOMA), with a trithiocarbonate reactive end-group was selected as the water-soluble living precursor and synthesized in situ via a RAFT aqueous solution polymerization process. The study focused on the polymerization of methyl methacrylate (MMA) at pH 3.5, 5 and 7 and its copolymerization with various proportions of styrene (S) at pH 3.5. In the Homopolymerization of MMA, the reaction was well-controlled at pH 3.5, while a low blocking efficiency was observed at higher pH. The systems led to spherical micelles, fibers and then vesicles when the molar mass of the hydrophobic block was increased, irrespective of the pH of the aqueous phase. In the case of the copolymerization with styrene at pH 3.5 and in chain length conditions leading to fibers for the Homopolymerization of MMA, the control was very good but the final morphology was that of spherical particles only, at all compositions studied, exactly like in the Homopolymerization of styrene performed under similar experimental conditions [Zhang et al. Macromolecules 2011; 44:7584–93]. The results were interpreted on the basis of an influence of the polymerization kinetics, especially in the early stage of the reaction in the aqueous phase.
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surfactant free controlled living radical emulsion co polymerization of n butyl acrylate and methyl methacrylate via raft using amphiphilic poly ethylene oxide based trithiocarbonate chain transfer agents
Macromolecules, 2009Co-Authors: Jutta Rieger, Gregor Osterwinter, Francois Stoffelbach, Bernadette CharleuxAbstract:The RAFT-mediated, surfactant-free, ab initio, batch emulsion polymerization of n-butyl acrylate (nBA) and its copolymerization with methyl methacrylate (MMA) were studied. The control agent was a surface-active trithiocarbonate macromolecular RAFT agent composed of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic dodecyl chain. The Homopolymerizations of nBA were fast with high final conversions, and the polymer chains were well-controlled with narrow molar mass distribution. The length of the PEO chain was shown to affect the particle size and the polymerization kinetics directly. We found the conditions to tune the particle size independently from the poly(n-butyl acrylate) chain length by playing with a mixture of macro-RAFT agents with long and short PEO segment or by adding a PEO-based nonionic surfactant. The copolymerizations of nBA and MMA exhibited features very similar to those of the nBA Homopolymerizations provided that the molar percentage of MMA did not exceed approximately ...
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nitroxide mediated miniemulsion polymerization ofn butyl acrylate synthesis of controlled homopolymers and gradient copolymers with styrene
Macromolecular Symposia, 2002Co-Authors: Celine Farcet, Bernadette Charleux, Rosangela PirriAbstract:Controlled free-radical Homopolymerization of n-butyl acrylate and its copolymerization with styrene have been studied in aqueous miniemulsion, using an acyclic β-phosphonylated nitroxide as a mediator, the N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide, also called SG1. Polymerization kinetics have been studied and characterization of the (co)polymers has been performed, demonstrating the successful synthesis of well-defined poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate-co-styrene) gradient copolymers.
Serge Creutz - One of the best experts on this subject based on the ideXlab platform.
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living anionic Homopolymerization and block copolymerization of dimethylamino ethyl methacrylate
Macromolecules, 1997Co-Authors: Serge Creutz, Philippe Teyssie, Robert JeromeAbstract:Anionic polymerization of (dimethylamino)ethyl methacrylate (DMAEMA) has been investigated in THF at −78 °C. The presence of lithium chloride has been shown to be desirable in order to afford a narrow molecular weight distribution as well as a good agreement between theoretical and observed molecular weight. The living character of the polymerization has been demonstrated. Thus the synthesis of block copolymers, some of them unattainable by GTP, has been carried out successfully. Finally, the anionic polymerization of mixtures of tert-butyl methacrylate (tBMA) and DMAEMA has been considered and their relative reactivity ratio estimated. The easy quaternization of (dimethylamino)ethyl methacrylate affords amphiphilic water-soluble copolymers displaying interesting characteristics as polymeric dispersants and surfactants.
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living anionic Homopolymerization and block copolymerization of dimethylamino ethyl methacrylate
Macromolecules, 1997Co-Authors: Serge Creutz, Philippe Teyssie, Robert JeromeAbstract:Anionic polymerization of (dimethylamino)ethyl methacrylate (DMAEMA) has been investigated in THF at −78 °C. The presence of lithium chloride has been shown to be desirable in order to afford a narrow molecular weight distribution as well as a good agreement between theoretical and observed molecular weight. The living character of the polymerization has been demonstrated. Thus the synthesis of block copolymers, some of them unattainable by GTP, has been carried out successfully. Finally, the anionic polymerization of mixtures of tert-butyl methacrylate (tBMA) and DMAEMA has been considered and their relative reactivity ratio estimated. The easy quaternization of (dimethylamino)ethyl methacrylate affords amphiphilic water-soluble copolymers displaying interesting characteristics as polymeric dispersants and surfactants.