The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Hugh Devlin - One of the best experts on this subject based on the ideXlab platform.
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Determination of Extent of Reaction in poly(mono- and dimethacrylates) using n.m.r. Comparison of solid-state and solution-state methods
Polymer, 1997Co-Authors: Frank Heatley, David C. Watts, Majid Ali, John Godward, Karl Stonebank, Hugh DevlinAbstract:Abstract The Extent of Reaction in lightly cross-linked poly(mono- and dimethacrylates) has been determined using solid- and liquid-state 13C n.m.r. Three methods were used: (i) magic-angle spinning (MAS) with high-power decoupling of the solid; (ii) conventional liquid-state high-resolution n.m.r. of the samples swollen by CDCl3; (iii) m.a.s. of the swollen samples. The three methods give comparable results, indicating that motional factors which may affect the solid-state method are not significant.
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Determination of Extent of Reaction in dimethacrylate-based dental composites using solid-state 13C m.a.s. n.m.r. spectroscopy and comparison with FTi.r. spectroscopy
Polymer, 1995Co-Authors: Frank Heatley, Yosthawee Pratsitsilp, Nicholas Mchugh, David C. Watts, Hugh DevlinAbstract:The instrumental conditions required for the determination of the Extent of Reaction in dimethacrylate-based dental composites using high-resolution solid-state 13C nuclear magnetic resonance (n.m.r.) techniques have been investigated. In the absence of paramagnetic fillers, clearly resolved carbonyl resonances for reacted and unreacted methacrylate groups were observed. The two peaks showed considerably different relaxation times using cross-polarization excitation, and accurate relative intensities could be only be obtained using direct excitation of the 13C nuclei with a pulse interval of at least 30s. Chemical shielding anisotropy spinning sidebands were observed for the reacted peak, but not for the unreacted. A spin-rate-dependent centreband intensity correction factor to account for this difference was evaluated using model triethyleneglycol dimethacrylate materials. The proportion of unreacted methacrylate groups determined using n.m.r. was essentially unaffected by spin rate, dipolar decoupling field strength and temperature, but was only about one-half that determined using infra-red spectroscopy. The origin of the discrepancy is as yet unclear.
Dean C. Webster - One of the best experts on this subject based on the ideXlab platform.
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surface microtopography in siloxane polyurethane thermosets the influence of siloxane and Extent of Reaction
Polymer, 2007Co-Authors: Partha Majumdar, Dean C. WebsterAbstract:Abstract The effect of polydimethylsiloxane (PDMS) content, PDMS molecular weight, and the Extent of prepolymerization Reactions between hydroxyl functional PDMS and polyisocyanate were explored in order to understand the influence of these variables on the formation of surface microtopography in a siloxane–polyurethane thermoset. The system is based on a difunctional hydroxyalkyl terminated PDMS, trifunctional poly(caprolactone) polyol, and a polyisocyanate. The effect of PDMS content was studied with PDMS of MW 1000 and 2000. PDMS of MW 1000 was varied from 5% to 15% and with PDMS of MW 2000 the level was varied from 5% to 12%. Tapping mode AFM images of the surface topography were used to characterize the system. The Extent of Reaction prior to film formation was studied by FTIR and correlated with microdomain formation in the final polymer film. Two different mixing strategies were explored: one where all of the ingredients were mixed together and a second approach where PDMS and polyisocyanate were mixed first, followed by the addition of the trifunctional polyol. Monte Carlo simulation of the polymerization with 10% PDMS of MW 1000 in the formulation revealed that there was a window of conversion for both PDMS and isocyanate at which the system spontaneously phase separates to form a microtopographical surface.
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Surface microtopography in siloxane–polyurethane thermosets: The influence of siloxane and Extent of Reaction
Polymer, 2007Co-Authors: Partha Majumdar, Dean C. WebsterAbstract:Abstract The effect of polydimethylsiloxane (PDMS) content, PDMS molecular weight, and the Extent of prepolymerization Reactions between hydroxyl functional PDMS and polyisocyanate were explored in order to understand the influence of these variables on the formation of surface microtopography in a siloxane–polyurethane thermoset. The system is based on a difunctional hydroxyalkyl terminated PDMS, trifunctional poly(caprolactone) polyol, and a polyisocyanate. The effect of PDMS content was studied with PDMS of MW 1000 and 2000. PDMS of MW 1000 was varied from 5% to 15% and with PDMS of MW 2000 the level was varied from 5% to 12%. Tapping mode AFM images of the surface topography were used to characterize the system. The Extent of Reaction prior to film formation was studied by FTIR and correlated with microdomain formation in the final polymer film. Two different mixing strategies were explored: one where all of the ingredients were mixed together and a second approach where PDMS and polyisocyanate were mixed first, followed by the addition of the trifunctional polyol. Monte Carlo simulation of the polymerization with 10% PDMS of MW 1000 in the formulation revealed that there was a window of conversion for both PDMS and isocyanate at which the system spontaneously phase separates to form a microtopographical surface.
Frank Heatley - One of the best experts on this subject based on the ideXlab platform.
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Determination of Extent of Reaction in poly(mono- and dimethacrylates) using n.m.r. Comparison of solid-state and solution-state methods
Polymer, 1997Co-Authors: Frank Heatley, David C. Watts, Majid Ali, John Godward, Karl Stonebank, Hugh DevlinAbstract:Abstract The Extent of Reaction in lightly cross-linked poly(mono- and dimethacrylates) has been determined using solid- and liquid-state 13C n.m.r. Three methods were used: (i) magic-angle spinning (MAS) with high-power decoupling of the solid; (ii) conventional liquid-state high-resolution n.m.r. of the samples swollen by CDCl3; (iii) m.a.s. of the swollen samples. The three methods give comparable results, indicating that motional factors which may affect the solid-state method are not significant.
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Determination of Extent of Reaction in dimethacrylate-based dental composites using solid-state 13C m.a.s. n.m.r. spectroscopy and comparison with FTi.r. spectroscopy
Polymer, 1995Co-Authors: Frank Heatley, Yosthawee Pratsitsilp, Nicholas Mchugh, David C. Watts, Hugh DevlinAbstract:The instrumental conditions required for the determination of the Extent of Reaction in dimethacrylate-based dental composites using high-resolution solid-state 13C nuclear magnetic resonance (n.m.r.) techniques have been investigated. In the absence of paramagnetic fillers, clearly resolved carbonyl resonances for reacted and unreacted methacrylate groups were observed. The two peaks showed considerably different relaxation times using cross-polarization excitation, and accurate relative intensities could be only be obtained using direct excitation of the 13C nuclei with a pulse interval of at least 30s. Chemical shielding anisotropy spinning sidebands were observed for the reacted peak, but not for the unreacted. A spin-rate-dependent centreband intensity correction factor to account for this difference was evaluated using model triethyleneglycol dimethacrylate materials. The proportion of unreacted methacrylate groups determined using n.m.r. was essentially unaffected by spin rate, dipolar decoupling field strength and temperature, but was only about one-half that determined using infra-red spectroscopy. The origin of the discrepancy is as yet unclear.
Partha Majumdar - One of the best experts on this subject based on the ideXlab platform.
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surface microtopography in siloxane polyurethane thermosets the influence of siloxane and Extent of Reaction
Polymer, 2007Co-Authors: Partha Majumdar, Dean C. WebsterAbstract:Abstract The effect of polydimethylsiloxane (PDMS) content, PDMS molecular weight, and the Extent of prepolymerization Reactions between hydroxyl functional PDMS and polyisocyanate were explored in order to understand the influence of these variables on the formation of surface microtopography in a siloxane–polyurethane thermoset. The system is based on a difunctional hydroxyalkyl terminated PDMS, trifunctional poly(caprolactone) polyol, and a polyisocyanate. The effect of PDMS content was studied with PDMS of MW 1000 and 2000. PDMS of MW 1000 was varied from 5% to 15% and with PDMS of MW 2000 the level was varied from 5% to 12%. Tapping mode AFM images of the surface topography were used to characterize the system. The Extent of Reaction prior to film formation was studied by FTIR and correlated with microdomain formation in the final polymer film. Two different mixing strategies were explored: one where all of the ingredients were mixed together and a second approach where PDMS and polyisocyanate were mixed first, followed by the addition of the trifunctional polyol. Monte Carlo simulation of the polymerization with 10% PDMS of MW 1000 in the formulation revealed that there was a window of conversion for both PDMS and isocyanate at which the system spontaneously phase separates to form a microtopographical surface.
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Surface microtopography in siloxane–polyurethane thermosets: The influence of siloxane and Extent of Reaction
Polymer, 2007Co-Authors: Partha Majumdar, Dean C. WebsterAbstract:Abstract The effect of polydimethylsiloxane (PDMS) content, PDMS molecular weight, and the Extent of prepolymerization Reactions between hydroxyl functional PDMS and polyisocyanate were explored in order to understand the influence of these variables on the formation of surface microtopography in a siloxane–polyurethane thermoset. The system is based on a difunctional hydroxyalkyl terminated PDMS, trifunctional poly(caprolactone) polyol, and a polyisocyanate. The effect of PDMS content was studied with PDMS of MW 1000 and 2000. PDMS of MW 1000 was varied from 5% to 15% and with PDMS of MW 2000 the level was varied from 5% to 12%. Tapping mode AFM images of the surface topography were used to characterize the system. The Extent of Reaction prior to film formation was studied by FTIR and correlated with microdomain formation in the final polymer film. Two different mixing strategies were explored: one where all of the ingredients were mixed together and a second approach where PDMS and polyisocyanate were mixed first, followed by the addition of the trifunctional polyol. Monte Carlo simulation of the polymerization with 10% PDMS of MW 1000 in the formulation revealed that there was a window of conversion for both PDMS and isocyanate at which the system spontaneously phase separates to form a microtopographical surface.
David C. Watts - One of the best experts on this subject based on the ideXlab platform.
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Determination of Extent of Reaction in poly(mono- and dimethacrylates) using n.m.r. Comparison of solid-state and solution-state methods
Polymer, 1997Co-Authors: Frank Heatley, David C. Watts, Majid Ali, John Godward, Karl Stonebank, Hugh DevlinAbstract:Abstract The Extent of Reaction in lightly cross-linked poly(mono- and dimethacrylates) has been determined using solid- and liquid-state 13C n.m.r. Three methods were used: (i) magic-angle spinning (MAS) with high-power decoupling of the solid; (ii) conventional liquid-state high-resolution n.m.r. of the samples swollen by CDCl3; (iii) m.a.s. of the swollen samples. The three methods give comparable results, indicating that motional factors which may affect the solid-state method are not significant.
-
Determination of Extent of Reaction in dimethacrylate-based dental composites using solid-state 13C m.a.s. n.m.r. spectroscopy and comparison with FTi.r. spectroscopy
Polymer, 1995Co-Authors: Frank Heatley, Yosthawee Pratsitsilp, Nicholas Mchugh, David C. Watts, Hugh DevlinAbstract:The instrumental conditions required for the determination of the Extent of Reaction in dimethacrylate-based dental composites using high-resolution solid-state 13C nuclear magnetic resonance (n.m.r.) techniques have been investigated. In the absence of paramagnetic fillers, clearly resolved carbonyl resonances for reacted and unreacted methacrylate groups were observed. The two peaks showed considerably different relaxation times using cross-polarization excitation, and accurate relative intensities could be only be obtained using direct excitation of the 13C nuclei with a pulse interval of at least 30s. Chemical shielding anisotropy spinning sidebands were observed for the reacted peak, but not for the unreacted. A spin-rate-dependent centreband intensity correction factor to account for this difference was evaluated using model triethyleneglycol dimethacrylate materials. The proportion of unreacted methacrylate groups determined using n.m.r. was essentially unaffected by spin rate, dipolar decoupling field strength and temperature, but was only about one-half that determined using infra-red spectroscopy. The origin of the discrepancy is as yet unclear.
