The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Bernard Boutevin - One of the best experts on this subject based on the ideXlab platform.
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reversible addition fragmentation chain transfer raft copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroixdesmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.
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Reversible addition‐fragmentation chain‐transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroix-desmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.
Romain Severac - One of the best experts on this subject based on the ideXlab platform.
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reversible addition fragmentation chain transfer raft copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroixdesmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.
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Reversible addition‐fragmentation chain‐transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroix-desmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.
Xiangming Kong - One of the best experts on this subject based on the ideXlab platform.
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Retardation Effect of pce superplasticizers with different architectures and their impacts on early strength of cement mortar
Cement & Concrete Composites, 2019Co-Authors: Xiangming Kong, Liran Zhang, Xia Miao, Shimin ZhouAbstract:Abstract As the most Effective superplasticizer, the comb-like PCE polymers also severely retard early cement hydration and hence decelerate early strength growth of concrete, which is undesired in some applications. In this study, a series of PCEs with different molecular architectures, including varied side chain length and density were synthetized by co-polymerizing acrylic acid and α-methallyl-ω-hydroxy poly(ethylene glycol) ether. Impacts of the obtained PCEs on cement hydration and early strength of mortar were investigated. Results show that adsorption of PCEs on cement grains is highly dependent on polymer architectures. Higher side chain length and density lead to lower adsorption amount and consequently higher early strength of mortar. It is interestingly found that the Retardation Effect of the PCEs on cement hydration is simply proportion to their absolute adsorption amounts on cement surface, while the complexation of R−COO− group with Ca2+, which is independent on polymer architectures, plays a minor role.
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Effect of highly carboxylated colloidal polymers on cement hydration and interactions with calcium ions
Cement and Concrete Research, 2018Co-Authors: Xiangming Kong, Chaoyang Zhang, Yi CaiAbstract:Abstract Polymer latexes are often found to retard cement hydration. Interaction of polymer particles with Ca2+ in pore solution and adsorption of polymer on cement were proposed as possible mechanisms for the Retardation Effect. This paper aims at disclosing the Retardation mechanism of colloidal polymers using a highly carboxylated polystyrene latex. Interaction between colloidal particles and Ca2+ was studied by post-treatment of the latex with Ca(NO3)2. Techniques including calorimetry, adsorption test, ICP-OES, SEM, are involved to investigate Effects of the post-treated latexes on hydrations of cement and C3S. It is found that enrichment of Ca2+ on surface of colloidal particles doesn't contribute to the Retardation Effect of polymer on cement hydration. Furthermore, the acceleration Effect of the two-step treated latex using Ca(NO3)2 and Na2SiO3 suggests that nucleation inhibition of the adsorbed polymer layer on cement surface is the more conceivable mechanism responsible for the Retardation Effect of the highly carboxylated latex.
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Interaction of silylated superplasticizers with cementitious materials
Journal of Applied Polymer Science, 2016Co-Authors: Zichen Lu, Xiangming Kong, Biqin Dong, Ziming Wang, Yanrong Zhang, Feng XingAbstract:Incorporation of silane groups into polycarboxylate superplasticizer (PCE) opens a new technical approach to improve properties of PCE, such as to enhance the adsorption of PCE on cement and hence the dispersing performance, to minimize the Retardation Effect, and potentially to increase mechanical strength of cement mortars. Silylated PCEs were synthesized using silane monomer via radical copolymerization. Dispersing Effect, adsorption behaviors, and influences on mortar strength of these polymers were systematically investigated. Results show that increasing the incorporation of sliane groups in PCE promotes the adsorption of polymer on cement surface and hence leads to good fluidity retention capability. Furthermore, sulfate resistance ability of silylated PCE is superior due to stronger chemical adsorption of polymer on cement surface. The Retardation Effect of PCE is minimized by the introduction of silane groups. The addition of silylated PCE significantly increases 3 days compressive strength without notably affecting the long-term strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44161.
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preparation of amphoteric polycarboxylate superplasticizers and their performances in cementitious system
Journal of Applied Polymer Science, 2015Co-Authors: Lingfei Jiang, Xiangming Kong, Zichen LuAbstract:A series of amphoteric polycarboxylate (PC) polymers were synthesized by radical copolymerization of acrylic acid (AA), (3-(methacryloylamino) propyl) trimethylammonium chloride (MAPTAC) and x-methoxypolyoxyethylene methacrylate ester (MPEGMA). Cationic groups were introduced in to PC molecules with expectation of less Retardation Effect on cement hydration compared to the traditional anionic PC superplasticizers. The content of cationic groups in polymer was varied by changing the monomer ratio of MAPTAC to AA in the synthesis recipes. The structure of the synthesized amphoteric PCs was verified by gel per- meation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The performances of the amphoteric PCs were evaluated by measurement of flowability and zeta-potential of cement pastes and adsorption amount of PC in cement pastes. Impacts of the PCs on cement hydration were studied by isothermal calorimetry. It is concluded that both anionic and cationic PC polymers can be Effectively adsorbed onto the surface of cement particles and thus change the zeta potential of cement pastes. The adsorption amounts of the amphoteric PCs decrease with increasing content of cationic units. A proper incorporation of cationic units into PC polymers may lead to a higher fluidizing performance in fresh cement pastes. The amphoteric PC polymers with higher content of cationic units show less Retardation Effect on cement hydration and hence higher early strength of cementitious materials may be achieved by using amphoteric PCs with appropriated content of cationic units without losing their plasticizing efficiency. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41348.
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Retardation Effect of styrene-acrylate copolymer latexes on cement hydration
Cement and Concrete Research, 2015Co-Authors: Xiangming Kong, Sebastian Emmerling, Joachim Pakusch, Markus Rueckel, Jörg NieberleAbstract:Interactions between styrene-acrylate latexes and cement are investigated with emphasis of the charge properties of the polymer particles by means of calorimetry, adsorption measurement, and confocal laser scanning microscope. Three latexes with varied surface charges of polymer particles were prepared by respectively using methacrylic acid (MAA), sodium styrene sulfonate (SSS) and methyl poly(ethylene glycol) methacrylate (MPEGMA) as water soluble monomers during synthesis. It is found that the polymer latexes retard cement hydration in two manners, namely the delaying Effect represented by a delayed hydration peak and the slowing down Effect characterized by a reduced main hydration peak during the acceleration period. The delaying Effect is closely related to the concentration of carboxylic groups existing in the latex, while the depression Effect of hydration rate is majorly caused by the adsorption of polymer particles on surface of cement grains and proportional to the total charge density of polymer particles.
Patrick Lacroixdesmazes - One of the best experts on this subject based on the ideXlab platform.
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reversible addition fragmentation chain transfer raft copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroixdesmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.
Patrick Lacroix-desmazes - One of the best experts on this subject based on the ideXlab platform.
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Reversible addition‐fragmentation chain‐transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate
Polymer International, 2002Co-Authors: Romain Severac, Patrick Lacroix-desmazes, Bernard BoutevinAbstract:The reversible addition-fragmentation chain-transfer (RAFT) copolymerization of vinylidene chloride and methyl acrylate was investigated at 70°C in benzene. Three dithioesters were synthesized in high yield by a simple and straightforward transesterification method. These dithioesters were successfully used as reversible chain-transfer agents, as demonstrated by the increase of molecular weight with conversion, a relatively low polydispersity index (I p =1.5) in comparison with a blank experiment (J p = 1.9), first-order polymerization kinetics and efficient chain extension. Nevertheless, a transfer reaction to vinylidene chloride monomer was considered to address the limitations of the RAFT process for this system. Moreover, a Retardation Effect was noticeable on the kinetics, depending on the structure and concentration of the transfer agent, leading to lower rate of polymerization for lower targeted molecular weights.