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Bob A. Howell - One of the best experts on this subject based on the ideXlab platform.
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thermal degradation of Vinylidene Chloride 4 t butoxycarbonyloxy phenyl methyl acrylate copolymers
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, D A Spears, Patrick B. SmithAbstract:Vinylidene Chloride polymers containing comonomer units capable of consuming evolved hydrogen Chloride to expose good radical-scavenging sites might be expected to display greater thermal stability than similar polymers containing simple alkyl acrylates as comonomer. Incorporation of a comonomer containing the phenyl t-butyl carbonate moiety into a Vinylidene Chloride polymer has the potential to afford a polymer with pendant groups which might interact with hydrogen Chloride to expose phenolic groups. Copolymers of Vinylidene Chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been prepared, characterized, and subjected to thermal degradation. The degradation has been characterized by thermal and spectroscopic techniques. The degradation of Vinylidene Chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers is much more facile than the same process for similar copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer degradation, [4-(t-butoxycarbonyloxy) phenylmethyl acrylate units are apparently converted to acrylic acid units by extensive fragmentation of the sidechain. Thus, the phenyl t-butyl carbonate moiety does function as a labile acid-sensitive pendant group but its decomposition in this instance leads to the generation of a phenoxybenzyl carboxylate capable of further fragmentation.
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Thermal degradation of Vinylidene Chloride/4-vinylpyridine copolymers
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Patrick B. SmithAbstract:Vinylidene Chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen Chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen Chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of Vinylidene Chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the Vinylidene Chloride segments of the polymer.
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kinetics of the thermal dehydrochlorination of Vinylidene Chloride barrier polymers
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. HowellAbstract:Vinylidene Chloride copolymers containing a predominance of Vinylidene Chloride (85-90%) have long been important barrier polymers widely used in the plastics packaging industry. These materials display excellent barrier to the ingress of oxygen and other small molecules (to prevent food spoilage) and to the loss of food flavor and aroma constituents (to prevent flavor scalping on the supermarket shelf). While these polymers have many outstanding characteristics, which have made them commercial successes, they tend to undergo thermally-induced degradative dehydrohalogenation at process temperatures. The dehydrochlorination occurs at moderate temperatures (120-200°C) and is a typical chain process involving initiation, propagation and termination phases. Defect structures, namely internal unsaturation (allylic dichloromethylene groups), serve as initiation sites for the degradation. These may be introduced during polymerization or during subsequent isolation and drying procedures. If uncontrolled, sequential dehydrohalogenation can lead to the formation of conjugated polyene sequences along the polymer mainchain. If sufficiently large, these polyenes absorb in the visible portion of the electromagnetic spectrum, and give rise to discoloration of the polymer. The dehydrochlorination process may be conveniently monitored by thermogravimetric techniques. Both initiation and propagation rate constants may be readily obtained.
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Thermal degradation of Vinylidene Chloride/vinyl Chloride copolymers in the presence of N-substituted maleimides
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Jin ZhangAbstract:As a consequence of their excellent barrier properties vinyl Chloride/Vinylidene Chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl Chloride/Vinylidene Chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.
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thermal degradation of Vinylidene Chloride vinyl Chloride copolymers in the presence of n substituted maleimides
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Jin ZhangAbstract:As a consequence of their excellent barrier properties vinyl Chloride/Vinylidene Chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl Chloride/Vinylidene Chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.
Patrick B. Smith - One of the best experts on this subject based on the ideXlab platform.
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thermal degradation of Vinylidene Chloride 4 t butoxycarbonyloxy phenyl methyl acrylate copolymers
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, D A Spears, Patrick B. SmithAbstract:Vinylidene Chloride polymers containing comonomer units capable of consuming evolved hydrogen Chloride to expose good radical-scavenging sites might be expected to display greater thermal stability than similar polymers containing simple alkyl acrylates as comonomer. Incorporation of a comonomer containing the phenyl t-butyl carbonate moiety into a Vinylidene Chloride polymer has the potential to afford a polymer with pendant groups which might interact with hydrogen Chloride to expose phenolic groups. Copolymers of Vinylidene Chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been prepared, characterized, and subjected to thermal degradation. The degradation has been characterized by thermal and spectroscopic techniques. The degradation of Vinylidene Chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers is much more facile than the same process for similar copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer degradation, [4-(t-butoxycarbonyloxy) phenylmethyl acrylate units are apparently converted to acrylic acid units by extensive fragmentation of the sidechain. Thus, the phenyl t-butyl carbonate moiety does function as a labile acid-sensitive pendant group but its decomposition in this instance leads to the generation of a phenoxybenzyl carboxylate capable of further fragmentation.
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Thermal degradation of Vinylidene Chloride/4-vinylpyridine copolymers
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Patrick B. SmithAbstract:Vinylidene Chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen Chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen Chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of Vinylidene Chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the Vinylidene Chloride segments of the polymer.
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Compositional and structural studies of Vinylidene Chloride/vinyl Chloride copolymers by pyrolysis gas chromatography.
Analytical Chemistry, 1996Co-Authors: Frank Cheng-yu Wang, Patrick B. SmithAbstract:: A pyrolysis gas chromatography approach has been developed to study the composition and structure of Vinylidene Chloride/vinyl Chloride copolymers. The composition and number average sequence length, which reflects the monomer arrangement in the polymer, were calculated using formulas that incorporate the pure trimer peak intensities and hybrid trimer peak intensities. Because of the reactivity difference between vinyl Chloride and Vinylidene Chloride monomers, the structure of the polymer has been further investigated on the basis of the percentage of grouped monomers (i.e., the number average sequence length for vinyl Chloride and Vinylidene Chloride repeat units). For the Vinylidene Chloride/vinyl Chloride copolymer examined in this study, the composition and number average sequence length elucidated from the pyrolysis gas chromatography study are compared to the product composition specification and/or the composition measured by (1)H-NMR.
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Thermal degradation characteristics of Vinylidene Chloride/2-[3,4-(1,1-dioxycyclopentyl)phenyl]ethyl acrylate copolymers
Thermochimica Acta, 1996Co-Authors: Bob A. Howell, S. I. Ahmed, B.b.s. Sastry, Patrick B. SmithAbstract:Abstract Vinylidene Chloride copolymers form the base for a significant segment of the barrier plastic packaging industry. While these materials have many superior properties they tend to undergo degradative dehydrochlorination at process temperatures. In an attempt to identify polymers which might display increased thermal stability, a series of Vinylidene Chloride/2-[3,4-(1,1-dioxycyclopentyl)phenyl]ethyl acrylate copolymers has been examined by thermogravimetry. These polymers contain a 3,4-dihydroxyphenyl pendant masked as the cyclopentanone ketal. In principle, this moiety could consume evolved hydrogen Chloride (to prevent its interaction with the walls of process equipment) to expose phenolic groups which might scavenge chlorine atoms. Both processes should enhance the stability of the polymeric system. In practice, copolymers containing 1.2, 2.6, 4.2 and 4.9 mol% 2-[3,4-(1,1-dioxycyclopentyl)phenyl]ethyl acrylate all undergo thermal degradation at approximately the same rate. The rate of decomposition of these copolymers, as reflected in both the rate constants ( k i ) for initiation and propagation ( k p ) of the degradation reaction, is not significantly different from that of the Vinylidene Chloride homopolymer.
Jin Zhang - One of the best experts on this subject based on the ideXlab platform.
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thermal degradation of Vinylidene Chloride vinyl Chloride copolymers in the presence of n substituted maleimides
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Jin ZhangAbstract:As a consequence of their excellent barrier properties vinyl Chloride/Vinylidene Chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl Chloride/Vinylidene Chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.
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Thermal degradation of Vinylidene Chloride/vinyl Chloride copolymers in the presence of N-substituted maleimides
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Bob A. Howell, Jin ZhangAbstract:As a consequence of their excellent barrier properties vinyl Chloride/Vinylidene Chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl Chloride/Vinylidene Chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.
Ravi Shankar - One of the best experts on this subject based on the ideXlab platform.
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poly Vinylidene Chloride co vinyl acetate comprehensive microstructure analysis by nmr spectroscopy
Polymer, 2005Co-Authors: A S Brar, Gurmeet Singh, Ravi ShankarAbstract:The microstructure analysis of poly(Vinylidene Chloride-co-vinyl acetate) was done using chemical shift modeling and 2D NMR spectroscopy. Chemical shift modeling was applied to analyze the compositional sensitive resonances of quaternary carbon of Vinylidene Chloride unit. Reactivity ratios determination was done from the diad and triad fractions. To resolve the complex 1H and 13C{1H} NMR spectra of copolymers, 2D 1H/13C hetero-nuclear single quantum coherence (HSQC), 1H/1H total correlation spectroscopy (TOCSY) and hetero-nuclear multiple bond correlation (HMBC) experiments were conducted. The combination of 2D NMR experiments supported by chemical shift modeling enabled to assign the complex and overlapping proton and carbon-13 resonances unambiguously.
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analysis of quaternary carbon resonances of Vinylidene Chloride methyl acrylate copolymers
European Polymer Journal, 2004Co-Authors: A S Brar, Gurmeet Singh, Ravi ShankarAbstract:Abstract Analysis of the quaternary carbon resonance signals of Vinylidene Chloride in Vinylidene Chloride (V)/methyl acrylate (M) copolymers at pentad level of compositional sensitivity is presented in this paper. The analysis has been done by resolving overlapped and complex resonance signals using an approach based on the intensities of resonances, chemical shift prediction and spectral simulation. Intensities of the resonance signals were calculated using the reactivity ratios optimized from the dyad and triad fractions, obtained from the 13C{1H} NMR data, by applying genetic algorithm. Joint confidence interval was obtained for the optimized reactivity ratios. The chemical shift modeling of the quaternary carbon resonance signals in terms of empirical additive parameters was done. The chemical shifts of overlapping pentad resonances were predicted from the empirical additive parameters optimized using genetic algorithm. Comparison of the intensities of pentad resonances assigned by chemical shift modeling and experimental intensities of resonances has been done to ascertain the assignments made. Comparison between simulated and experimental spectra at pentad level of sensitivity has been done.
A S Brar - One of the best experts on this subject based on the ideXlab platform.
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poly Vinylidene Chloride co vinyl acetate comprehensive microstructure analysis by nmr spectroscopy
Polymer, 2005Co-Authors: A S Brar, Gurmeet Singh, Ravi ShankarAbstract:The microstructure analysis of poly(Vinylidene Chloride-co-vinyl acetate) was done using chemical shift modeling and 2D NMR spectroscopy. Chemical shift modeling was applied to analyze the compositional sensitive resonances of quaternary carbon of Vinylidene Chloride unit. Reactivity ratios determination was done from the diad and triad fractions. To resolve the complex 1H and 13C{1H} NMR spectra of copolymers, 2D 1H/13C hetero-nuclear single quantum coherence (HSQC), 1H/1H total correlation spectroscopy (TOCSY) and hetero-nuclear multiple bond correlation (HMBC) experiments were conducted. The combination of 2D NMR experiments supported by chemical shift modeling enabled to assign the complex and overlapping proton and carbon-13 resonances unambiguously.
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analysis of quaternary carbon resonances of Vinylidene Chloride methyl acrylate copolymers
European Polymer Journal, 2004Co-Authors: A S Brar, Gurmeet Singh, Ravi ShankarAbstract:Abstract Analysis of the quaternary carbon resonance signals of Vinylidene Chloride in Vinylidene Chloride (V)/methyl acrylate (M) copolymers at pentad level of compositional sensitivity is presented in this paper. The analysis has been done by resolving overlapped and complex resonance signals using an approach based on the intensities of resonances, chemical shift prediction and spectral simulation. Intensities of the resonance signals were calculated using the reactivity ratios optimized from the dyad and triad fractions, obtained from the 13C{1H} NMR data, by applying genetic algorithm. Joint confidence interval was obtained for the optimized reactivity ratios. The chemical shift modeling of the quaternary carbon resonance signals in terms of empirical additive parameters was done. The chemical shifts of overlapping pentad resonances were predicted from the empirical additive parameters optimized using genetic algorithm. Comparison of the intensities of pentad resonances assigned by chemical shift modeling and experimental intensities of resonances has been done to ascertain the assignments made. Comparison between simulated and experimental spectra at pentad level of sensitivity has been done.