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Thomas P. Davis - One of the best experts on this subject based on the ideXlab platform.
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chain length dependent Termination Rate coefficients of methyl methacrylate mma in the gel regime accessing kti i using reversible addition fragmentation chain transfer raft polymerization
Macromolecules, 2007Co-Authors: Geoffrey Johnstonhall, Thomas P. Davis, Martina H. Stenzel, Christopher Barnerkowollik, Michael J. MonteiroAbstract:The Termination Rate coefficient, k(t)(i,i), for propagating chains of near equal length, i, was evaluated using the RAFT-CLD-T method over a wide range of chain lengths and up to a conversion of 70% for MMA polymerizations carried out in the presence of the RAFT agent, CPDB, at 80 degrees C. We found that the conversion for the gel onset corresponded to the conversion at which polymer chains begin to overlap (i.e., c*), and was found to range from 15 to 30% conversion depending on the M-n. It was further shown that c* also corresponded with the gel onset conversions for vinyl acetate and methyl acrylate. The chain length dependence of k(t) in the gel regime scaled as alpha(gel)(x) = 1.8x + 0.056, suggesting that reptation alone does not play a role in our system. A composite model was then derived to accuRately describe k(t)(i,i) for chain lengths up to 3200 and conversions up to 70%. The k(t)(i,i) profiles for well-known Termination models were tested and most gave unsatisfactory agreement with our experiments. Our model can be readily applied to any monomer provided accuRate k(t)(i,i)(x) data can be determined.
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obtaining chain length dependent Termination Rate coefficients via thermally initiated reversible addition fragmentation chain transfer experiments current status and future challenges
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:The reversible addition fragmentation chain transfer (RAFT) process can be utilized in conjunction with Rate of polymerization measurements to accuRately map the chain length dependence of the Termination Rate coefficient. This novel approach was originally applied to styrene polymerization and has been termed the RAFT chain length dependent Termination (RAFT-CLD-T) method. The RAFT-CLD-T technique is discussed in the context of the prerequisite analysis parameters as well as the choice of RAFT agent. In the present contribution we critically compare the data obtained via RAFT-CLD-T thus far for the monomers styrene (Sty), methyl methacrylate (MMA), methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), and vinyl acetate (VAc). For monomers with relatively low reactivity propagating radicals (MMA), a strong chain length dependence of kt in the small chain length regime was observed, indicated by a relatively high α value (in the frequently used expression k t i,i = kt 0·l -α). With increasing chain length, the α value is continuously decreasing, caused by a slow transition from translational diffusion to segmental diffusion as predicted by the composite model of chain length dependent Termination. For monomers with higher reactivity propagating radicals (MA, VAc), a linear dependence of kt with chain length was observed (α = 0.36 for MA and 0.09 for VAc). Within the acrylate class, an interesting influence of the side chain was found. In the small chain length regime, α is increasing with increasing length of the side chain from 0.36 in case of MA to 1.2 in DA, which may be attributed to an increased shielding of the polymeric radical. At longer chain lengths, the α value of MA is significantly higher than those for BA and DA, where a is strongly decreasing with increasing chain length. This may indicate a different flexibility and coil structure of MA compared to BA and DA. In general, the acrylates display significantly higher a values in the long chain region than MMA and VAc, which we assign to the presence of mid-chain radicals. The data obtained via three dimensional simultaneous mapping of the chain length and conversion dependence of kt (3D-RAFT-CLD-T) for MA and VAc are also highlighted. © 2006 American Chemical Society.
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Accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry: A theoretical study
Macromolecules, 2006Co-Authors: Tara M. Lovestead, Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT−CLD−T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, . In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input k...
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accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry a theoretical study
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Tara M. Lovestead, Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT-CLD-T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, Kts.l. In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input kinetic parameters, and whether the geometric or the harmonic mean approximation is assumed for the relationship between k t and the individual radical chain lengths s and l. Thus, for the first time a facile and accuRate method for quantification of kt s,l; is validated theoretically allowing for a complete characterization of free radical Termination processes for dispaRate length radicals. © 2006 American Chemical Society.
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accessing chain length dependent Termination Rate coefficients of methyl methacrylate mma via the reversible addition fragmentation chain transfer raft process
Macromolecular Chemistry and Physics, 2005Co-Authors: Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Michael J. Monteiro, Geoffrey Johnstonhall, Christopher BarnerkowollikAbstract:The RAFT-CLD-T methodology is demonstRated to be not only applicable to 1-substituted monomers such as styrene and acrylates, but also to 1,1-disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 degrees C. The evolution of the chain length dependent Termination Rate coefficient, k(t)(i,i), was constructed in a step-wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k(t) in MMA polymerizations is compatible with the composite model for chain length dependent Termination. For the initial chain-length regime, up to a degree of polymerization of 100, k(t) decreases with alpha (in the expression k(t)(i,i) = k(t)(0) . i(-alpha)) being close to 0.65 at 80 degrees C. At chain lengths exceeding 100, the decrease is less pronounced (affording an alpha of 0.15 at 80 degrees C). However, the data are best represented by a continuously decreasing nonlinear functionality implying a chain length dependent alpha.
Christopher Barner-kowollik - One of the best experts on this subject based on the ideXlab platform.
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Design Criteria for AccuRate Measurement of Bimolecular Radical Termination Rate Coefficients via the RAFT-CLD-T Method
Macromolecular Theory and Simulations, 2008Co-Authors: Geoffrey Johnston-hall, Christopher Barner-kowollik, Michael J. MonteiroAbstract:The reversible addition-fragmentation chain transfer chain length dependent Termination (RAFT-CLD-T) technique allows a simple experimental approach to obtain chain-length-dependent Termination Rate coefficients as a function of conversion, k(x). This work provides a set of criteria by which accuRate k(x) can be obtained using the RAFT-CLD-T method. Visualization of three-dimensional plots varying all kinetic Rate parameters and starting concentrations demonstRates that only certain combinations give an accuRate extraction of k(x). The current study provides hands-on guidelines for experimentalists applying the RAFT-CLD-T method.
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Accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry: A theoretical study
Macromolecules, 2006Co-Authors: Tara M. Lovestead, Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT−CLD−T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, . In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input k...
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Access to Chain Length Dependent Termination Rate Coefficients of Methyl Acrylate via Reversible Addition−Fragmentation Chain Transfer Polymerization
Macromolecules, 2005Co-Authors: Alexander Theis, Thomas P. Davis, Achim Feldermann, Nathalie Charton, Martina H. Stenzel, Christopher Barner-kowollikAbstract:The reversible addition−fragmentation chain transferchain length dependentTermination (RAFT-CLD-T) method is employed to map out the chain length dependence of the Termination Rate coefficient in methyl acrylate (MA) bulk free radical polymerizations at 80 °C. Methoxycarbonylethyl phenyldithioacetate (MCEPDA)a novel RAFT agent carrying a methyl acryl leaving groupis identified as suitable for the RAFT-CLD-T method applied to methyl acrylate, as interfering inhibition and Rate retardation effects are avoided. The chain length dependency of the Termination Rate coefficient was constructed in a stepwise fashion since the MA/MCEPDA system displays hybrid behavior (between conventional and living free radical polymerization), resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The chain length dependency of kt in the MA system for chain lengths, i, ranging from 5 to 800 at 80 °C may be described by a value for α of 0.36 ± 0.05 (where α is the slope of the associated log...
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Mapping Chain Length and Conversion Dependent Termination Rate Coefficients in Methyl Acrylate Free Radical Polymerization
Macromolecules, 2005Co-Authors: Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:The mapping of the Termination Rate coefficient as a function of the chain lengths of the terminating radicals using the reversible addition fragmentation chain transfer (RAFT) polymerization process was investigated. Methyl acrylate (MA) was freed from inhibitor by percolating over a column of activated basic alumina. Solutions of MS with AIBN and methyl propionate for the deTermination of the monomer reaction order or RAFT agent for the CLD-T measurements were thoroughly deoxygenated via for subsequent freeze-pump-thaw cycles. MA free radical polymerization displayed nonidealities due to the presence of less reactive midchain radicals.
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Facile Access to Chain Length Dependent Termination Rate Coefficients via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization: Influence of the RAFT Agent Structure
Macromolecules, 2004Co-Authors: Achim Feldermann, Philipp Vana, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:A recently developed methodology for determining chain length dependent Termination Rate coefficients, 〈kti,i〉, via reversible addition−fragmentation chain transfer (RAFT) polymerizations has been extended and validated for 1-phenylethyl phenyldithioacetate (PEPDA) and 3-benzylsulfanylthiocarbonylsulfanylpropionic acid (BSPA) mediated styrene (bulk) free radical polymerizations at 80 °C. While the use of cumyl phenyldithioacetate (CPDA) enables a highly precise mapping of the chain length dependence of the Termination Rate coefficient, employment of PEPDA and BSPA leads to considerable information loss for short chain lengths (i < 10). Careful simulations demonstRate that such behavior is caused by a substantial decrease in the initial transfer effectiveness of the RAFT agents when going from CPDA to BSPA, leading to hybrid behavior between conventional and living free radical polymerization. The observed hybrid behavior is quantifiable via (overall) transfer Rate coefficients for the individual RAFT agen...
Christopher Barnerkowollik - One of the best experts on this subject based on the ideXlab platform.
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design criteria for accuRate measurement of bimolecular radical Termination Rate coefficients via the raft cld t method
Institute for Future Environments; Science & Engineering Faculty, 2008Co-Authors: Geoffrey Johnstonhall, Christopher Barnerkowollik, Michael J. MonteiroAbstract:The reversible addition-fragmentation chain transfer chain length dependent Termination (RAFT-CLD-T) technique allows a simple experimental approach to obtain chain-lengthdependent Termination Rate coefficients as a function of conversion, kt i,i(x). This work provides a set of criteria by which accuRate kt i,i (x) can be obtained using the RAFT-CLD-T method. Visualization of three-dimensional plots varying all kinetic Rate parameters and starting concentrations demonstRates that only certain combinations give an accuRate extraction of kt i,i (x). The current study provides hands-on guidelines for experimentalists applying the RAFT-CLD-T method. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.
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chain length dependent Termination Rate coefficients of methyl methacrylate mma in the gel regime accessing kti i using reversible addition fragmentation chain transfer raft polymerization
Macromolecules, 2007Co-Authors: Geoffrey Johnstonhall, Thomas P. Davis, Martina H. Stenzel, Christopher Barnerkowollik, Michael J. MonteiroAbstract:The Termination Rate coefficient, k(t)(i,i), for propagating chains of near equal length, i, was evaluated using the RAFT-CLD-T method over a wide range of chain lengths and up to a conversion of 70% for MMA polymerizations carried out in the presence of the RAFT agent, CPDB, at 80 degrees C. We found that the conversion for the gel onset corresponded to the conversion at which polymer chains begin to overlap (i.e., c*), and was found to range from 15 to 30% conversion depending on the M-n. It was further shown that c* also corresponded with the gel onset conversions for vinyl acetate and methyl acrylate. The chain length dependence of k(t) in the gel regime scaled as alpha(gel)(x) = 1.8x + 0.056, suggesting that reptation alone does not play a role in our system. A composite model was then derived to accuRately describe k(t)(i,i) for chain lengths up to 3200 and conversions up to 70%. The k(t)(i,i) profiles for well-known Termination models were tested and most gave unsatisfactory agreement with our experiments. Our model can be readily applied to any monomer provided accuRate k(t)(i,i)(x) data can be determined.
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obtaining chain length dependent Termination Rate coefficients via thermally initiated reversible addition fragmentation chain transfer experiments current status and future challenges
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:The reversible addition fragmentation chain transfer (RAFT) process can be utilized in conjunction with Rate of polymerization measurements to accuRately map the chain length dependence of the Termination Rate coefficient. This novel approach was originally applied to styrene polymerization and has been termed the RAFT chain length dependent Termination (RAFT-CLD-T) method. The RAFT-CLD-T technique is discussed in the context of the prerequisite analysis parameters as well as the choice of RAFT agent. In the present contribution we critically compare the data obtained via RAFT-CLD-T thus far for the monomers styrene (Sty), methyl methacrylate (MMA), methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), and vinyl acetate (VAc). For monomers with relatively low reactivity propagating radicals (MMA), a strong chain length dependence of kt in the small chain length regime was observed, indicated by a relatively high α value (in the frequently used expression k t i,i = kt 0·l -α). With increasing chain length, the α value is continuously decreasing, caused by a slow transition from translational diffusion to segmental diffusion as predicted by the composite model of chain length dependent Termination. For monomers with higher reactivity propagating radicals (MA, VAc), a linear dependence of kt with chain length was observed (α = 0.36 for MA and 0.09 for VAc). Within the acrylate class, an interesting influence of the side chain was found. In the small chain length regime, α is increasing with increasing length of the side chain from 0.36 in case of MA to 1.2 in DA, which may be attributed to an increased shielding of the polymeric radical. At longer chain lengths, the α value of MA is significantly higher than those for BA and DA, where a is strongly decreasing with increasing chain length. This may indicate a different flexibility and coil structure of MA compared to BA and DA. In general, the acrylates display significantly higher a values in the long chain region than MMA and VAc, which we assign to the presence of mid-chain radicals. The data obtained via three dimensional simultaneous mapping of the chain length and conversion dependence of kt (3D-RAFT-CLD-T) for MA and VAc are also highlighted. © 2006 American Chemical Society.
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accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry a theoretical study
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Tara M. Lovestead, Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT-CLD-T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, Kts.l. In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input kinetic parameters, and whether the geometric or the harmonic mean approximation is assumed for the relationship between k t and the individual radical chain lengths s and l. Thus, for the first time a facile and accuRate method for quantification of kt s,l; is validated theoretically allowing for a complete characterization of free radical Termination processes for dispaRate length radicals. © 2006 American Chemical Society.
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accessing chain length dependent Termination Rate coefficients of methyl methacrylate mma via the reversible addition fragmentation chain transfer raft process
Macromolecular Chemistry and Physics, 2005Co-Authors: Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Michael J. Monteiro, Geoffrey Johnstonhall, Christopher BarnerkowollikAbstract:The RAFT-CLD-T methodology is demonstRated to be not only applicable to 1-substituted monomers such as styrene and acrylates, but also to 1,1-disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 degrees C. The evolution of the chain length dependent Termination Rate coefficient, k(t)(i,i), was constructed in a step-wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k(t) in MMA polymerizations is compatible with the composite model for chain length dependent Termination. For the initial chain-length regime, up to a degree of polymerization of 100, k(t) decreases with alpha (in the expression k(t)(i,i) = k(t)(0) . i(-alpha)) being close to 0.65 at 80 degrees C. At chain lengths exceeding 100, the decrease is less pronounced (affording an alpha of 0.15 at 80 degrees C). However, the data are best represented by a continuously decreasing nonlinear functionality implying a chain length dependent alpha.
Martina H. Stenzel - One of the best experts on this subject based on the ideXlab platform.
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chain length dependent Termination Rate coefficients of methyl methacrylate mma in the gel regime accessing kti i using reversible addition fragmentation chain transfer raft polymerization
Macromolecules, 2007Co-Authors: Geoffrey Johnstonhall, Thomas P. Davis, Martina H. Stenzel, Christopher Barnerkowollik, Michael J. MonteiroAbstract:The Termination Rate coefficient, k(t)(i,i), for propagating chains of near equal length, i, was evaluated using the RAFT-CLD-T method over a wide range of chain lengths and up to a conversion of 70% for MMA polymerizations carried out in the presence of the RAFT agent, CPDB, at 80 degrees C. We found that the conversion for the gel onset corresponded to the conversion at which polymer chains begin to overlap (i.e., c*), and was found to range from 15 to 30% conversion depending on the M-n. It was further shown that c* also corresponded with the gel onset conversions for vinyl acetate and methyl acrylate. The chain length dependence of k(t) in the gel regime scaled as alpha(gel)(x) = 1.8x + 0.056, suggesting that reptation alone does not play a role in our system. A composite model was then derived to accuRately describe k(t)(i,i) for chain lengths up to 3200 and conversions up to 70%. The k(t)(i,i) profiles for well-known Termination models were tested and most gave unsatisfactory agreement with our experiments. Our model can be readily applied to any monomer provided accuRate k(t)(i,i)(x) data can be determined.
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obtaining chain length dependent Termination Rate coefficients via thermally initiated reversible addition fragmentation chain transfer experiments current status and future challenges
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:The reversible addition fragmentation chain transfer (RAFT) process can be utilized in conjunction with Rate of polymerization measurements to accuRately map the chain length dependence of the Termination Rate coefficient. This novel approach was originally applied to styrene polymerization and has been termed the RAFT chain length dependent Termination (RAFT-CLD-T) method. The RAFT-CLD-T technique is discussed in the context of the prerequisite analysis parameters as well as the choice of RAFT agent. In the present contribution we critically compare the data obtained via RAFT-CLD-T thus far for the monomers styrene (Sty), methyl methacrylate (MMA), methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), and vinyl acetate (VAc). For monomers with relatively low reactivity propagating radicals (MMA), a strong chain length dependence of kt in the small chain length regime was observed, indicated by a relatively high α value (in the frequently used expression k t i,i = kt 0·l -α). With increasing chain length, the α value is continuously decreasing, caused by a slow transition from translational diffusion to segmental diffusion as predicted by the composite model of chain length dependent Termination. For monomers with higher reactivity propagating radicals (MA, VAc), a linear dependence of kt with chain length was observed (α = 0.36 for MA and 0.09 for VAc). Within the acrylate class, an interesting influence of the side chain was found. In the small chain length regime, α is increasing with increasing length of the side chain from 0.36 in case of MA to 1.2 in DA, which may be attributed to an increased shielding of the polymeric radical. At longer chain lengths, the α value of MA is significantly higher than those for BA and DA, where a is strongly decreasing with increasing chain length. This may indicate a different flexibility and coil structure of MA compared to BA and DA. In general, the acrylates display significantly higher a values in the long chain region than MMA and VAc, which we assign to the presence of mid-chain radicals. The data obtained via three dimensional simultaneous mapping of the chain length and conversion dependence of kt (3D-RAFT-CLD-T) for MA and VAc are also highlighted. © 2006 American Chemical Society.
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accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry a theoretical study
Institute for Future Environments; Science & Engineering Faculty, 2006Co-Authors: Tara M. Lovestead, Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT-CLD-T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, Kts.l. In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input kinetic parameters, and whether the geometric or the harmonic mean approximation is assumed for the relationship between k t and the individual radical chain lengths s and l. Thus, for the first time a facile and accuRate method for quantification of kt s,l; is validated theoretically allowing for a complete characterization of free radical Termination processes for dispaRate length radicals. © 2006 American Chemical Society.
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Accessing the chain length dependence of the Termination Rate coefficient for dispaRate length radicals via reversible addition fragmentation chain transfer chemistry: A theoretical study
Macromolecules, 2006Co-Authors: Tara M. Lovestead, Alexander Theis, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent Termination (RAFT−CLD−T) method, a novel approach is presented to access the Termination Rate coefficient for dispaRate length radicals, . In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to geneRate two nearly monodisperse chain length distributions with dispaRate average lengths, s and l. These dispaRate length radicals are geneRated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstRates that the chain length dependence of the Termination Rate coefficient for dispaRate length radicals can be obtained accuRately regardless of the extent of the prepolymerization period of the polyRAFT species, the input k...
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accessing chain length dependent Termination Rate coefficients of methyl methacrylate mma via the reversible addition fragmentation chain transfer raft process
Macromolecular Chemistry and Physics, 2005Co-Authors: Thomas P. Davis, Alexander Theis, Martina H. Stenzel, Michael J. Monteiro, Geoffrey Johnstonhall, Christopher BarnerkowollikAbstract:The RAFT-CLD-T methodology is demonstRated to be not only applicable to 1-substituted monomers such as styrene and acrylates, but also to 1,1-disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 degrees C. The evolution of the chain length dependent Termination Rate coefficient, k(t)(i,i), was constructed in a step-wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k(t) in MMA polymerizations is compatible with the composite model for chain length dependent Termination. For the initial chain-length regime, up to a degree of polymerization of 100, k(t) decreases with alpha (in the expression k(t)(i,i) = k(t)(0) . i(-alpha)) being close to 0.65 at 80 degrees C. At chain lengths exceeding 100, the decrease is less pronounced (affording an alpha of 0.15 at 80 degrees C). However, the data are best represented by a continuously decreasing nonlinear functionality implying a chain length dependent alpha.
Achim Feldermann - One of the best experts on this subject based on the ideXlab platform.
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access to chain length dependent Termination Rate coefficients of methyl acrylate via reversible addition fragmentation chain transfer polymerization
Macromolecules, 2005Co-Authors: Alexander Theis, Thomas P. Davis, Achim Feldermann, Nathalie Charton, Martina H. Stenzel, Christopher BarnerkowollikAbstract:The reversible addition−fragmentation chain transferchain length dependentTermination (RAFT-CLD-T) method is employed to map out the chain length dependence of the Termination Rate coefficient in methyl acrylate (MA) bulk free radical polymerizations at 80 °C. Methoxycarbonylethyl phenyldithioacetate (MCEPDA)a novel RAFT agent carrying a methyl acryl leaving groupis identified as suitable for the RAFT-CLD-T method applied to methyl acrylate, as interfering inhibition and Rate retardation effects are avoided. The chain length dependency of the Termination Rate coefficient was constructed in a stepwise fashion since the MA/MCEPDA system displays hybrid behavior (between conventional and living free radical polymerization), resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The chain length dependency of kt in the MA system for chain lengths, i, ranging from 5 to 800 at 80 °C may be described by a value for α of 0.36 ± 0.05 (where α is the slope of the associated log...
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Access to Chain Length Dependent Termination Rate Coefficients of Methyl Acrylate via Reversible Addition−Fragmentation Chain Transfer Polymerization
Macromolecules, 2005Co-Authors: Alexander Theis, Thomas P. Davis, Achim Feldermann, Nathalie Charton, Martina H. Stenzel, Christopher Barner-kowollikAbstract:The reversible addition−fragmentation chain transferchain length dependentTermination (RAFT-CLD-T) method is employed to map out the chain length dependence of the Termination Rate coefficient in methyl acrylate (MA) bulk free radical polymerizations at 80 °C. Methoxycarbonylethyl phenyldithioacetate (MCEPDA)a novel RAFT agent carrying a methyl acryl leaving groupis identified as suitable for the RAFT-CLD-T method applied to methyl acrylate, as interfering inhibition and Rate retardation effects are avoided. The chain length dependency of the Termination Rate coefficient was constructed in a stepwise fashion since the MA/MCEPDA system displays hybrid behavior (between conventional and living free radical polymerization), resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The chain length dependency of kt in the MA system for chain lengths, i, ranging from 5 to 800 at 80 °C may be described by a value for α of 0.36 ± 0.05 (where α is the slope of the associated log...
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chain length dependence of Termination Rate coefficients in acrylate and methacrylate homopolymerizations investigated via the sp plp technique
Macromolecules, 2004Co-Authors: Michael Buback, Mark Egorov, Achim FeldermannAbstract:Termination Rate coefficients, kt, of alkyl acrylate and alkyl methacrylate homopolymerizations at 40 °C and pressures of 1000 and 2000 bar have been measured up to high degrees of monomer conversion using the time-resolved single-pulse−pulsed-laser polymerization (SP−PLP) technique. The chain-length dependence (CLD) of kt has been deduced from SP−PLP data by adopting the power-law model, kt = i-α, where i is the chain length. For methacrylates at low degrees of monomer conversion, α is close to the theoretically predicted value of 0.16. At conversions above 20% the exponent α increases significantly with increasing conversion. This effect becomes particularly pronounced in the gel effect region, where α, e.g. for MMA, reaches values close to unity. In the case of acrylates with small alkyl ester side chain, such as methyl acrylate, α is also close to 0.16 at low conversions and increases toward higher conversions. In the case of acrylates with larger alkyl ester side chain, such as dodecyl acrylate and 2...
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Facile Access to Chain Length Dependent Termination Rate Coefficients via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization: Influence of the RAFT Agent Structure
Macromolecules, 2004Co-Authors: Achim Feldermann, Philipp Vana, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-kowollikAbstract:A recently developed methodology for determining chain length dependent Termination Rate coefficients, 〈kti,i〉, via reversible addition−fragmentation chain transfer (RAFT) polymerizations has been extended and validated for 1-phenylethyl phenyldithioacetate (PEPDA) and 3-benzylsulfanylthiocarbonylsulfanylpropionic acid (BSPA) mediated styrene (bulk) free radical polymerizations at 80 °C. While the use of cumyl phenyldithioacetate (CPDA) enables a highly precise mapping of the chain length dependence of the Termination Rate coefficient, employment of PEPDA and BSPA leads to considerable information loss for short chain lengths (i < 10). Careful simulations demonstRate that such behavior is caused by a substantial decrease in the initial transfer effectiveness of the RAFT agents when going from CPDA to BSPA, leading to hybrid behavior between conventional and living free radical polymerization. The observed hybrid behavior is quantifiable via (overall) transfer Rate coefficients for the individual RAFT agen...
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facile access to chain length dependent Termination Rate coefficients via reversible addition fragmentation chain transfer raft polymerization influence of the raft agent structure
Institute for Future Environments; Science & Engineering Faculty, 2004Co-Authors: Achim Feldermann, Philipp Vana, Thomas P. Davis, Martina H. Stenzel, Christopher BarnerkowollikAbstract:A recently developed methodology for determining chain length dependent Termination Rate coefficients, 〈kt i,i〉, via reversible addition-fragmentation chain transfer (RAFT) polymerizations has been extended and validated for 1-phenylethyl phenyldithioacetate (PEPDA) and 3-benzylsulfanylthiocarbo-nylsulfanylpropionic acid (BSPA) mediated styrene (bulk) free radical polymerizations at 80°C. While the use of cumyl phenyldithioacetate (CPDA) enables a highly precise mapping of the chain length dependence of the Termination Rate coefficient, employment of PEPDA and BSPA leads to considerable information loss for short chain lengths (i < 10). Careful simulations demonstRate that such behavior is caused by a substantial decrease in the initial transfer effectiveness of the RAFT agents when going from CPDA to BSPA, leading to hybrid behavior between conventional and living free radical polymerization. The observed hybrid behavior is quantifiable via (overall) transfer Rate coefficients for the individual RAFT agents in the preequilibrium step [CPDA (ktr,R = 5.0 × 105 L mol-1 s-1), PEPDA (ktr,R = 2.0 × 10 5 L mol-1 s-1), and BSPA (ktr,R = 1.0 × 104 L mol-1 s-1) at 80°C]. The underlying structural cause is the change from a tertiary (CPDA), via a secondary (PEPDA), to a primary (BSPA) leaving group in the initial RAFT agent. Further, the presented simulations open an efficient pathway for approximating overall preequilibrium transfer Rate coefficients for the employed RAFT agents.