The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Qi Wang - One of the best experts on this subject based on the ideXlab platform.
-
enhancement of ultrasonically initiated emulsion Polymerization Rate using aliphatic alcohols as hydroxyl radical scavengers
Ultrasonics Sonochemistry, 2008Co-Authors: Qi WangAbstract:Abstract Ultrasonically initiated emulsion Polymerization of styrene was carried out in the presence of aliphatic alcohols, e.g. methanol, ethanol, n -pronanol and n -butanol, as volatile hydroxyl radical scavengers. With the addition of methanol, the Polymerization Rate of styrene increased, while the molecular weight and the average particle size of the produced polystyrene decreased because more radicals were produced in the presence of methanol. This is true also for the other Polymerization system using other aliphatic alcohols, such as ethanol, n -pronanol and n -butanol, suggesting that the alcohols enter into cavitation bubbles and further react with hydroxyl radicals ( OH) from the sonolysis of water to produce hydroxyalkyl radicals, so as to reduce the recombination of H and OH radicals, therefore more radicals will be present in the systems for initiating Polymerization. Obviously, it is an effective way to enhance ultrasonically initiated emulsion Polymerization Rate of styrene by adding volatile hydroxyl radical scavenger.
-
Polymerization Rate and mechanism of ultrasonically initiated emulsion Polymerization of n butyl acrylate
Ultrasonics Sonochemistry, 2002Co-Authors: Qi Wang, Yongqin Liao, Xi Xu, Steven Michael Baxter, Robert Victor Slone, Shuguang Wu, Graham Swift, David G WestmorelandAbstract:The factors affecting the induction period and Polymerization Rate in ultrasonically initiated emulsion Polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion Polymerization of BA without any added initiator by enhancing the N2 flow Rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced Polymerization Rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The Polymerization Rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion Polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical Polymerization mechanism for ultrasonically initiated emulsion Polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of Polymerization and the Polymerization process. Compared with conventional emulsion Polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion Polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster Polymerization Rate, and higher molecular weight of the polymer prepared.
Bryan W. Boudouris - One of the best experts on this subject based on the ideXlab platform.
-
Polymerization Rate Considerations for High Molecular Weight Polyisoprene‐b‐Polystyrene‐b‐Poly(N,N‐dimethylacrylamide) Triblock Polymers Synthesized Via Sequential Reversible Addition‐Fragmentation Chain Transfer (RAFT) Reactions
Macromolecular Chemistry and Physics, 2015Co-Authors: Ryan A. Mulvenna, Rafael A. Prato, William A. Phillip, Bryan W. BoudourisAbstract:The reversible addition-fragmentation chain transfer (RAFT) Polymerization mechanism is a powerful technique for synthesizing functional block polymers for myriad applications. Most kinetic studies regarding the RAFT mechanism have focused on low molecular weight homopolymer and block polymer syntheses using a dithiobenzoate chain transfer agent (CTA). Here, the Polymerization kinetics are evaluated for a high molecular weight A-B-C triblock polymer system, polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA), using a trithiocarbonate agent for application of these types of polymers. Importantly, it is demonstRated that the Polymerization of polyisoprene is the step that geneRates the block with the largest dispersity for high molecular weight PI-PS-PDMA polymers. As such, the kinetics of isoprene Polymerization must be altered systematically for desired nanostructures to be formed. In addition, it is established that the PS and PDMA block additions exhibit Polymerization Rate retardation, which is due to slow chain fragmentation of the CTA, as demonstRated by the magnitudes of the equilibrium constants for both the styrene and N,N-dimethylacrylamide reactions, and as calculated using ab initio modeling. This elucidation of the nature of the controlled RAFT mechanism provides a critical handle for the more precise design and control of other next-generation high molecular weight block polymer systems that are polymerized using the RAFT mechanism.
-
Polymerization Rate considerations for high molecular weight polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) triblock polymers synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) reactions
Macromolecular Chemistry and Physics, 2015Co-Authors: Ryan A. Mulvenna, Rafael A. Prato, William A. Phillip, Bryan W. BoudourisAbstract:The reversible addition-fragmentation chain transfer (RAFT)\nPolymerization mechanism is a powerful technique for synthesizing\nfunctional block polymers for myriad applications. Most kinetic studies\nregarding the RAFT mechanism have focused on low molecular weight\nhomopolymer and block polymer syntheses using a dithiobenzoate chain\ntransfer agent (CTA). Here, the Polymerization kinetics are evaluated\nfor a high molecular weight A-B-C triblock polymer system,\npolyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA),\nusing a trithiocarbonate agent for application of these types of\npolymers. Importantly, it is demonstRated that the Polymerization of\npolyisoprene is the step that geneRates the block with the largest\ndispersity for high molecular weight PI-PS-PDMA polymers. As such, the\nkinetics of isoprene Polymerization must be altered systematically for\ndesired nanostructures to be formed. In addition, it is established that\nthe PS and PDMA block additions exhibit Polymerization Rate retardation,\nwhich is due to slow chain fragmentation of the CTA, as demonstRated by\nthe magnitudes of the equilibrium constants for both the styrene and\nN,N-dimethylacrylamide reactions, and as calculated using ab initio\nmodeling. This elucidation of the nature of the controlled RAFT\nmechanism provides a critical handle for the more precise design and\ncontrol of other next-generation high molecular weight block polymer\nsystems that are polymerized using the RAFT mechanism.
David G Westmoreland - One of the best experts on this subject based on the ideXlab platform.
-
Polymerization Rate and mechanism of ultrasonically initiated emulsion Polymerization of n butyl acrylate
Ultrasonics Sonochemistry, 2002Co-Authors: Qi Wang, Yongqin Liao, Xi Xu, Steven Michael Baxter, Robert Victor Slone, Shuguang Wu, Graham Swift, David G WestmorelandAbstract:The factors affecting the induction period and Polymerization Rate in ultrasonically initiated emulsion Polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion Polymerization of BA without any added initiator by enhancing the N2 flow Rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced Polymerization Rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The Polymerization Rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion Polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical Polymerization mechanism for ultrasonically initiated emulsion Polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of Polymerization and the Polymerization process. Compared with conventional emulsion Polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion Polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster Polymerization Rate, and higher molecular weight of the polymer prepared.
Ryan A. Mulvenna - One of the best experts on this subject based on the ideXlab platform.
-
Polymerization Rate Considerations for High Molecular Weight Polyisoprene‐b‐Polystyrene‐b‐Poly(N,N‐dimethylacrylamide) Triblock Polymers Synthesized Via Sequential Reversible Addition‐Fragmentation Chain Transfer (RAFT) Reactions
Macromolecular Chemistry and Physics, 2015Co-Authors: Ryan A. Mulvenna, Rafael A. Prato, William A. Phillip, Bryan W. BoudourisAbstract:The reversible addition-fragmentation chain transfer (RAFT) Polymerization mechanism is a powerful technique for synthesizing functional block polymers for myriad applications. Most kinetic studies regarding the RAFT mechanism have focused on low molecular weight homopolymer and block polymer syntheses using a dithiobenzoate chain transfer agent (CTA). Here, the Polymerization kinetics are evaluated for a high molecular weight A-B-C triblock polymer system, polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA), using a trithiocarbonate agent for application of these types of polymers. Importantly, it is demonstRated that the Polymerization of polyisoprene is the step that geneRates the block with the largest dispersity for high molecular weight PI-PS-PDMA polymers. As such, the kinetics of isoprene Polymerization must be altered systematically for desired nanostructures to be formed. In addition, it is established that the PS and PDMA block additions exhibit Polymerization Rate retardation, which is due to slow chain fragmentation of the CTA, as demonstRated by the magnitudes of the equilibrium constants for both the styrene and N,N-dimethylacrylamide reactions, and as calculated using ab initio modeling. This elucidation of the nature of the controlled RAFT mechanism provides a critical handle for the more precise design and control of other next-generation high molecular weight block polymer systems that are polymerized using the RAFT mechanism.
-
Polymerization Rate considerations for high molecular weight polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) triblock polymers synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) reactions
Macromolecular Chemistry and Physics, 2015Co-Authors: Ryan A. Mulvenna, Rafael A. Prato, William A. Phillip, Bryan W. BoudourisAbstract:The reversible addition-fragmentation chain transfer (RAFT)\nPolymerization mechanism is a powerful technique for synthesizing\nfunctional block polymers for myriad applications. Most kinetic studies\nregarding the RAFT mechanism have focused on low molecular weight\nhomopolymer and block polymer syntheses using a dithiobenzoate chain\ntransfer agent (CTA). Here, the Polymerization kinetics are evaluated\nfor a high molecular weight A-B-C triblock polymer system,\npolyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA),\nusing a trithiocarbonate agent for application of these types of\npolymers. Importantly, it is demonstRated that the Polymerization of\npolyisoprene is the step that geneRates the block with the largest\ndispersity for high molecular weight PI-PS-PDMA polymers. As such, the\nkinetics of isoprene Polymerization must be altered systematically for\ndesired nanostructures to be formed. In addition, it is established that\nthe PS and PDMA block additions exhibit Polymerization Rate retardation,\nwhich is due to slow chain fragmentation of the CTA, as demonstRated by\nthe magnitudes of the equilibrium constants for both the styrene and\nN,N-dimethylacrylamide reactions, and as calculated using ab initio\nmodeling. This elucidation of the nature of the controlled RAFT\nmechanism provides a critical handle for the more precise design and\ncontrol of other next-generation high molecular weight block polymer\nsystems that are polymerized using the RAFT mechanism.
Eduardo Vivaldo-lima - One of the best experts on this subject based on the ideXlab platform.
-
Effect of initiator type and concentration on Polymerization Rate and molecular weight in the bimolecular nitroxide‐mediated radical Polymerization of styrene
Advances in Polymer Technology, 2010Co-Authors: Telma Nogueira, Liliane M F Lona, Neil T Mcmanus, Eduardo Vivaldo-lima, Maria Cecilia Gonçalves, Alexander PenlidisAbstract:To increase the Polymerization Rate in the bimolecular nitroxide-mediated radical Polymerization (NMRP) of styrene, without using expensive non-commercial reagents, an experimental study using 2,2,6,6-tetramethyl-1-piperidinoxyl as a controller and tert-butylperoxy 2-ethylhexyl carbonate (TBEC) as the initiator was carried out. The basis for comparison was the bimolecular NMRP of styrene with dibenzoyl peroxide as initiator. It was found that faster Polymerization Rates and still relatively low polydispersities were possible using TBEC. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:11–19, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20170
-
Effect of Stabilizer Concentration, Pressure and Temperature on Polymerization Rate and Molecular Weight Development in RAFT Polymerization of MMA in scCO2
Macromolecular Symposia, 2010Co-Authors: Gabriel Jaramillo-soto, Pedro R. García-morán, Eduardo Vivaldo-limaAbstract:An experimental study on the effect of stabilizer concentration, pressure (100 to 500 bar), and temperature (6 5 to 85 °C) on Polymerization Rate and molecular weight development in the reversible addition-fragmentation chain transfer (RAFT) Polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO 2 ) is presented. AIBN was used as initiator, S-Thiobenzoyl thioglycolic acid as RAFT agent, and Krytox ® 257 FSL as stabilizer. It was observed that the Polymerization proceeded in a controlled manner. High conversions can be reached in reasonable times. Fairly low polydispersities (around 1 . 2 ) are possible if either pressure or temperature are increased, but better results are obtained if the Polymerization proceeds at the upper temperature value of 8 5 °C.
-
Effect of stabilizer concentration and controller structure and composition on Polymerization Rate and molecular weight development in RAFT Polymerization of styrene in supercritical carbon dioxide
Polymer, 2009Co-Authors: Gabriel Jaramillo-soto, Pedro R. García-morán, Francisco J. Enríquez-medrano, Hortensia Maldonado-textle, Martha Albores-velasco, Ramiro Guerrero-santos, Eduardo Vivaldo-limaAbstract:An experimental study on the reversible addition-fragmentation chain transfer (RAFT) Polymerization of styrene in supercritical carbon dioxide is presented. A 38 mL, high-pressure view cell with two frontal and two lateral sapphire windows was used as reactor. Poly(styrene-block-dimethylsiloxane) was used as stabilizer. The performance as RAFT controllers of S-thiobenzoyl thioglycolic acid, methyl naphthalene dithiobenzoate, 4-methyl allyl dithiobenzoate, and benzyl-N,N-dimethyldithiocarbamate was compared. The effect of stabilizer concentration and controller structure and concentration on Polymerization Rate and molecular weight development was analyzed. Good performance was obtained with the first three controllers, although simultaneous high Polymerization Rates and low polydispersities were not possible with either of them. The performance of the fourth RAFT controller was poor.
-
Effect of the addition of inert or TEMPO-capped prepolymer on Polymerization Rate and molecular weight development in the nitroxide-mediated radical Polymerization of styrene
Journal of Applied Polymer Science, 2008Co-Authors: Martha Roa‐luna, Liliane M F Lona, Neil T Mcmanus, Eduardo Vivaldo-lima, Afsaneh Nabifar, Alexander PenlidisAbstract:The importance of diffusion-controlled (DC) effects on controlled radical Polymerization (CRP) processes has been rather controversial and usually considered only if there is some mismatch between experimental data and model predictions of Polymerization Rate and molecular weight averages. Results from an experimental study designed to create conditions in which DC effects may be present from the outset for the bimolecular nitroxide-mediated radical Polymerization (NMRP) of styrene in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), are presented herein. The experiments consisted of adding size exclusion chromatography (SEC) polystyrene (PS) standards or nitroxyl-capped PS (of different molecular weights, in several proportions), to a conventional recipe of bimolecular NMRP of styrene, and studying the effect of their presence on Polymerization Rate and molecular weight development. A previously developed kinetic model for NMRP of styrene was modified to take into account the presence of prepolymer as an inert “solvent,” or as a monomolecular “controller” of high molecular weight. The effects of DC reactions (propagation, termination, activation, and deactivation of polymer radicals) were modeled using conventional free-volume theory. Reasonably, good agreement between experimental data and model predictions with either modeling approach was obtained. It was concluded that DC effects are weak in the NMRP of styrene, even in the presence of prepolymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
-
Assessing the Importance of Diffusion‐Controlled Effects on Polymerization Rate and Molecular Weight Development in Nitroxide‐Mediated Radical Polymerization of Styrene
Journal of Macromolecular Science Part A, 2007Co-Authors: Martha Roa‐luna, Liliane M F Lona, Neil T Mcmanus, Eduardo Vivaldo-lima, Martha Patricia Díaz‐barber, Alexander PenlidisAbstract:A previously derived kinetic model for the nitroxide‐mediated radical Polymerization (NMRP) of styrene has been modified by considering diffusion‐controlled (DC) effects on the bimolecular radical termination, monomer propagation, dormant polymer activation, and polymer radical deactivation reactions. Free‐volume theory was used to incorpoRate the DC‐effects into the model. It was found that DC‐termination enhances the living behavior of the system, whereas DC‐propagation, DC‐activation and DC‐deactivation worsen it. Although the inclusion of overall DC‐effects into the kinetic model improved the performance of the model by slightly reducing the deviations obtained from experimental data of Polymerization Rate and molecular weight in the bimolecular NMRP of styrene with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), it does not seem to justify adding the extra four free‐volume parameters. In the case of the semi‐batch addition of azo‐bis‐iso‐butyronitrile (AIBN) (several single...