Arthur Woodward - Academia.edu (original) (raw)
Papers by Arthur Woodward
Macromolecules, 1984
We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the stu... more We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the study of solution-grown polymer single crystals. Two samples of 1,4-trans-polybutadiene (it?,, = 9.8 x IO3 and 1.7 X lo4), grown from 0.01% heptane solution, were employed. With the appropriate use of magic-angle spinning and proton decoupling it is possible to measure chemical shifts, relaxation times, and nuclear Overhauser enhancements (NOE) of carbon nuclei in the crystal stems and amorphous regicms; the latter are assumed to consist exclusively of fold surfaces and cilia. Using dipolar decoupling but without magic-angle spinning, we examined the chemical shift anisotropy of the olefinic carbons. The powder pattern is asymmetric with a (ull -u33) of ca. 178 ppm. Using magic-angle spinning with dipolar decoupling but without lH-13C cross polarization, we have determined the fraction of crystallinity as 0.73 * 0.01 for both samples, in agreement with estimates from densities. Spin-lattice relaxation of the fold-surface carbons is shown to be predominantly dipolar. The less than maximal NOE values-ca. 2-are consistent with anisotropic chain motion. Both these findings and the chemical shifts of the fold-surface carbons agree with those reported by Jelinski et al." for bulk amorphous polybutadiene. The chemical shifts of the methylene carbons in the folds can be rationalized on the basis of the y-gauche shielding effect and the accepted rotational isomeric state model for unperturbed 1,4-trans-polybutadiene, but the upfield shift of the olefinic carbons is less than expected. It appears that the motions and conformations of the surface folds are similar to those of bulk polymer despite the constraints imposed on the folds by the requirement of adjacent reentry, established in a previous high-resolution study.1° Upon epoxidation with m-chloroperbenzoic acid, the folds give very broad carbon-13 resonances. Evidently, the introduction of oxirane rings immobilizes the chains sufficiently to prevent averaging of lH-13C dipolar interactions and 13C chemical shift anisotropies.
The American Journal of Human Genetics, Oct 31, 2006
Schizophrenia and human leukocyte antigen (HLA) matching between couples or between mothers and o... more Schizophrenia and human leukocyte antigen (HLA) matching between couples or between mothers and offspring have independently been associated with prenatal/obstetric complications, including preeclampsia and low birth weight. Here, we report the results of a family-based candidate-gene study that brings together these two disparate lines of research by assessing maternal-fetal genotype matching at HLA-A, -B, and -DRB1 as a risk factor of schizophrenia. We used a conditional-likelihood modeling approach with a sample of 274 families that had at least one offspring with schizophrenia or a related spectrum disorder. A statistically significant HLA-B maternal-fetal genotype-matching effect on schizophrenia was demonstrated for female offspring ( ; parameter estimate 1.7 [95% confidence interval 1.22-2.49]). Because P p .01 the matching effect could be associated with pregnancy complications rather than with schizophrenia per se, these findings are consistent with the neurodevelopmental hypothesis of schizophrenia and with accumulating evidence that the prenatal period is involved in the origins of this disease. Our approach demonstrates how genetic markers can be used to characterize the biology of prenatal risk factors of schizophrenia.
Theory and Research in Social Education, 2004
Psychometrika, 1973
Abstract For random-model, fully-crossed, two-and three-facet experimental designs the following ... more Abstract For random-model, fully-crossed, two-and three-facet experimental designs the following two problems were considered. First, equations were developed for determining the optimal number of conditions of a facet for maximizing the coefficient of generalizability ...
Macromolecules, 1984
trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were... more trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were crystallized from solutions, mainly at a concentration of 1 g/100 cm3, by cooling directly from 100 OC to an (apparent) TC of -15 to +32 OC, by precooling to 0 "C, redissolving a t 35-45 "C, and crystallizing at Tc, and by cooling to 0 OC and heating to 10,20, or 30 "C. Most of the structures obtained were characterized, while suspended in the crystallization liquid, by interference contrast microscopy and with crossed polaroids; the crystalline fraction from the density and the crystal form from X-ray diffraction and differential scanning calorimetry were determined for the dry products. The morphology obtained by direct crystallization was dependent on molecular weight, crystallization temperature, and solvent, with a-and 0-hedrites (sheaves), a-and 0-spherulites, and 0-aggregates of cup-shaped lamellas being found. The precooling method yielded overgrown lamellas in most cases; however, more complex morphologies developed when the thermal history was changed. The density depended on molecular weight, concentration, and crystallization temperature. The crystallinity was mainly a function of crystal form and molecular weight. The equation of Tseng, Herman, Woodward, and Newman was used to explain the molecular weight dependence of the crystallinity at low M, and to calculate the average number of monomer units per fold and interlamellar traverse. Epoxidation of some TPI structures suspended in amyl acetate a t 0 "C was carried out. At high concentrations of the epoxidizing agent, m-chloroperbenzoic acid, the fraction epoxidized approached or exceeded the noncrystalline fraction as obtained from density measurement.
Multivariate Behavioral Research, 1975
ABSTRACT
trans-1,4-Polybutadiene (TPBD) fractions (Mu = 7000-36000) with a 1% cis content were crystallize... more trans-1,4-Polybutadiene (TPBD) fractions (Mu = 7000-36000) with a 1% cis content were crystallized from solution as a function of crystallization solvent, temperature, and concentration. The resulting structures were characterized quantitatively by using epoxidation in suspension followed by carbon-13 NMR measurement in solution, which yields the fraction reacted and the unreacted and reacted block lengths, A and B, respectively. Agreement between the fraction epoxidized and the noncrystalline fraction from density measurement was obtained. Evidence for the rejection of cis units from the trans-polybutadiene crystal core was found from the carbon-13 NMR studies. Although the amorphous (surface) fraction remains constant, A, equated to the number of monomer units per crystal traverse, and B, equated to the average number of monomer units per fold, increase with crystallization temperature. A and B remain constant with a change in morphology from single lamellar to multilamellar and with crystallization concentration from 0.05% to 5% w/v. The average number of TPBD units rejected from the crystal core when cis unit rejection occurs is estimated and the average length of a fold containing no cis unit is found to be 3-5 units.
Fourier transform infrared spectra were obtained for solution-crystallized samples of two polybut... more Fourier transform infrared spectra were obtained for solution-crystallized samples of two polybutadiene copolymers, one containing 10% cis-, 1,5% 1,2and 88,5% transand the other 1 070 cis-and 99% trans-polybutadiene. Measurements were made at room temperature, at temperatures above the crystal transition temperature, but below the melting temperature, and at temperatures above the melting temperature. Spectra for 100% crystalline samples were obtained by subtraction of the spectrum for the melt from that for the semicrystalline sample. Infrared spectra were also obtained for suspension epoxidized samples; these showed the presence of an unreacted crystal core and completely reacted lamellar surfaces.
A Simplified Conjoint Expected Risk (SCER: Holtgrave and Weber, 1993) model-based approach was us... more A Simplified Conjoint Expected Risk (SCER: Holtgrave and Weber, 1993) model-based approach was used to explore differences in the perceived risk of a variety of financial and health activities among Caucasians, African-Americans, Mexican-Americans, and Taiwanese-Americans. The SCER model postulates that the perceived risk of an activity is a function of five dimensions: the subjective probability of harm, benefit, and status quo, and the subjective expected harm and benefit. This model offers a framework in which to apply qualitative and quantitative approaches in order to identify and to assess the generality of ethnic group differences in the relative weight attached to probability and expected outcome information, the subjective valuation of probabilities and expected outcomes, and the perceived harms and benefits. Results demonstrated that the primary and most generalised locus of ethnic group perceived risk differences is the relative importance attached to probability and expe...
Risk Analysis, 2000
The simplified Conjoint Expected Risk (CER) model by Holtgrave and Weber posits that perceived ri... more The simplified Conjoint Expected Risk (CER) model by Holtgrave and Weber posits that perceived risk is a linear combination of the subjective judgments of the probabilities of harm, benefit, and status quo, and the expected harm and benefit of an activity. It modifies Luce and Weber's original CER model-that uses objective information to evaluate financial gambles-to accommodate activities such as health/technology activities where values of the model variables are subjective. If the simplified model is a valid modification of the original model, its performance should not be sensitive to the use of subjective information. However, because people may evaluate information differently when objective information is provided to them than when they generate information on their own, the performance of the simplified CER model may not be robust to the source of model-variable information. We compared the use of objective and subjective information, and results indicate that the estimates of the simplified CER model parameters and the proportion of variance in risk judgments accounted for by the model are similar under these two conditions. Thus, the simplified CER model is viable with activities for which harm and benefit information is subjective.
Macromolecules, 1983
... Susan Tseng and Arthur E. Woodward Department of Chemistry, City University of New York, City... more ... Susan Tseng and Arthur E. Woodward Department of Chemistry, City University of New York, City College, New York, New York 10031. ... These conditions were determined by measurement of 13C spin-lattice relaxation and nuclear Overhauser enhancement (NOE). ...
Macromolecules, 1988
trans-1,4-Polyisoprene structures in the a and @ crystalline forms with various morphologies were... more trans-1,4-Polyisoprene structures in the a and @ crystalline forms with various morphologies were prepared by using different crystallization procedures. The effects of molecular weight, crystallization temperature, and annealing treatment on the crystalline stem length and the noncrystalline traverse length were investigated by using epoxidation in suspension followed by carbon-13 solution NMR. Preliminary studies were carried out to determine the optimum conditions for quantitative reaction of the double bonds a t the lamellar surfaces. Results were obtained suggesting that for many liquids penetration of partially reacted lamellas can take place from the lateral surfaces; reactant concentration and time were also shown to be important and conditions were found that gave agreement between the fraction reacted and the noncrystalline fraction from infrared and density measurements. Interlamellar traverses were detected in multilamellar structures with the amount increasing with increasing molecular weight. The nature of chain folding in the trans-polydienes is discussed.
Macromolecules, 1984
We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the stu... more We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the study of solution-grown polymer single crystals. Two samples of 1,4-trans-polybutadiene (it?,, = 9.8 x IO3 and 1.7 X lo4), grown from 0.01% heptane solution, were employed. With the appropriate use of magic-angle spinning and proton decoupling it is possible to measure chemical shifts, relaxation times, and nuclear Overhauser enhancements (NOE) of carbon nuclei in the crystal stems and amorphous regicms; the latter are assumed to consist exclusively of fold surfaces and cilia. Using dipolar decoupling but without magic-angle spinning, we examined the chemical shift anisotropy of the olefinic carbons. The powder pattern is asymmetric with a (ull -u33) of ca. 178 ppm. Using magic-angle spinning with dipolar decoupling but without lH-13C cross polarization, we have determined the fraction of crystallinity as 0.73 * 0.01 for both samples, in agreement with estimates from densities. Spin-lattice relaxation of the fold-surface carbons is shown to be predominantly dipolar. The less than maximal NOE values-ca. 2-are consistent with anisotropic chain motion. Both these findings and the chemical shifts of the fold-surface carbons agree with those reported by Jelinski et al." for bulk amorphous polybutadiene. The chemical shifts of the methylene carbons in the folds can be rationalized on the basis of the y-gauche shielding effect and the accepted rotational isomeric state model for unperturbed 1,4-trans-polybutadiene, but the upfield shift of the olefinic carbons is less than expected. It appears that the motions and conformations of the surface folds are similar to those of bulk polymer despite the constraints imposed on the folds by the requirement of adjacent reentry, established in a previous high-resolution study.1° Upon epoxidation with m-chloroperbenzoic acid, the folds give very broad carbon-13 resonances. Evidently, the introduction of oxirane rings immobilizes the chains sufficiently to prevent averaging of lH-13C dipolar interactions and 13C chemical shift anisotropies.
Macromolecules, 1984
trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were... more trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were crystallized from solutions, mainly at a concentration of 1 g/100 cm3, by cooling directly from 100 OC to an (apparent) TC of -15 to +32 OC, by precooling to 0 "C, redissolving a t 35-45 "C, and crystallizing at Tc, and by cooling to 0 OC and heating to 10,20, or 30 "C. Most of the structures obtained were characterized, while suspended in the crystallization liquid, by interference contrast microscopy and with crossed polaroids; the crystalline fraction from the density and the crystal form from X-ray diffraction and differential scanning calorimetry were determined for the dry products. The morphology obtained by direct crystallization was dependent on molecular weight, crystallization temperature, and solvent, with a-and 0-hedrites (sheaves), a-and 0-spherulites, and 0-aggregates of cup-shaped lamellas being found. The precooling method yielded overgrown lamellas in most cases; however, more complex morphologies developed when the thermal history was changed. The density depended on molecular weight, concentration, and crystallization temperature. The crystallinity was mainly a function of crystal form and molecular weight. The equation of Tseng, Herman, Woodward, and Newman was used to explain the molecular weight dependence of the crystallinity at low M, and to calculate the average number of monomer units per fold and interlamellar traverse. Epoxidation of some TPI structures suspended in amyl acetate a t 0 "C was carried out. At high concentrations of the epoxidizing agent, m-chloroperbenzoic acid, the fraction epoxidized approached or exceeded the noncrystalline fraction as obtained from density measurement.
Macromolecules, 1987
A statistical model based on the assumption of adjacent reentry in lamellas of trans-l,4polybutad... more A statistical model based on the assumption of adjacent reentry in lamellas of trans-l,4polybutadiene chains, containing randomly placed cis units, is developed for the calculation of crystallinity and of a NMR tetrad ratio in surface reacted specimens. In this treatment the chain ends and cis units appear at the lamellar surfaces and there are three types of chain folds: (i) those containing only trans-polybutadiene units and which have a constant length, (ii) those with interior cis Units with the same length for the all-trans fold, and (iii) those with cis units and accompanying trans units rejected from the crystal core, having a variable length. In this treatment the crystallinity and tetrad ratio are functions of (i) the cis content, (ii) the degree of polymerization, (iii) the crystal traverse length, and (iv) the all-trans-containing fold length, B'. Comparison of calculated with experimental values yields 4 f 1 for B'.
Macromolecules, 1988
Copolymers of trans-1,4-polyisoprene containing from 1 to 10% randomly placed epoxidized units we... more Copolymers of trans-1,4-polyisoprene containing from 1 to 10% randomly placed epoxidized units were crystallized from solution. The crystal form from infrared spectroscopy, the DSC melting endotherm(s), and the reacted and unreacted block lengths, as obtained by surface epoxidation in suspension followed by carbon-13 solution NMR, were determined. Small amounts of oxirane units (1-2%) have no significant effect on the melting endotherm or block lengths but do change the crystal form and the redissolution temperature. Evidence for incorporation of oxirane units in the crystal core is discussed.
Journal of the American Chemical Society, 1953
Page 1. Dec. 20, 1953 Low TEMPERATURE AUTOXIDATION OF HYDROCARBONS 6189 [CONTRIBUTION FROM THE PO... more Page 1. Dec. 20, 1953 Low TEMPERATURE AUTOXIDATION OF HYDROCARBONS 6189 [CONTRIBUTION FROM THE POLYMER RESEARCH INSTITUTE, POLYTECHNIC INSTITUTE OF BROOKLYN] Low Temperature Autoxidation of Hydrocarbons. ...
Macromolecules, 1984
We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the stu... more We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the study of solution-grown polymer single crystals. Two samples of 1,4-trans-polybutadiene (it?,, = 9.8 x IO3 and 1.7 X lo4), grown from 0.01% heptane solution, were employed. With the appropriate use of magic-angle spinning and proton decoupling it is possible to measure chemical shifts, relaxation times, and nuclear Overhauser enhancements (NOE) of carbon nuclei in the crystal stems and amorphous regicms; the latter are assumed to consist exclusively of fold surfaces and cilia. Using dipolar decoupling but without magic-angle spinning, we examined the chemical shift anisotropy of the olefinic carbons. The powder pattern is asymmetric with a (ull -u33) of ca. 178 ppm. Using magic-angle spinning with dipolar decoupling but without lH-13C cross polarization, we have determined the fraction of crystallinity as 0.73 * 0.01 for both samples, in agreement with estimates from densities. Spin-lattice relaxation of the fold-surface carbons is shown to be predominantly dipolar. The less than maximal NOE values-ca. 2-are consistent with anisotropic chain motion. Both these findings and the chemical shifts of the fold-surface carbons agree with those reported by Jelinski et al." for bulk amorphous polybutadiene. The chemical shifts of the methylene carbons in the folds can be rationalized on the basis of the y-gauche shielding effect and the accepted rotational isomeric state model for unperturbed 1,4-trans-polybutadiene, but the upfield shift of the olefinic carbons is less than expected. It appears that the motions and conformations of the surface folds are similar to those of bulk polymer despite the constraints imposed on the folds by the requirement of adjacent reentry, established in a previous high-resolution study.1° Upon epoxidation with m-chloroperbenzoic acid, the folds give very broad carbon-13 resonances. Evidently, the introduction of oxirane rings immobilizes the chains sufficiently to prevent averaging of lH-13C dipolar interactions and 13C chemical shift anisotropies.
The American Journal of Human Genetics, Oct 31, 2006
Schizophrenia and human leukocyte antigen (HLA) matching between couples or between mothers and o... more Schizophrenia and human leukocyte antigen (HLA) matching between couples or between mothers and offspring have independently been associated with prenatal/obstetric complications, including preeclampsia and low birth weight. Here, we report the results of a family-based candidate-gene study that brings together these two disparate lines of research by assessing maternal-fetal genotype matching at HLA-A, -B, and -DRB1 as a risk factor of schizophrenia. We used a conditional-likelihood modeling approach with a sample of 274 families that had at least one offspring with schizophrenia or a related spectrum disorder. A statistically significant HLA-B maternal-fetal genotype-matching effect on schizophrenia was demonstrated for female offspring ( ; parameter estimate 1.7 [95% confidence interval 1.22-2.49]). Because P p .01 the matching effect could be associated with pregnancy complications rather than with schizophrenia per se, these findings are consistent with the neurodevelopmental hypothesis of schizophrenia and with accumulating evidence that the prenatal period is involved in the origins of this disease. Our approach demonstrates how genetic markers can be used to characterize the biology of prenatal risk factors of schizophrenia.
Theory and Research in Social Education, 2004
Psychometrika, 1973
Abstract For random-model, fully-crossed, two-and three-facet experimental designs the following ... more Abstract For random-model, fully-crossed, two-and three-facet experimental designs the following two problems were considered. First, equations were developed for determining the optimal number of conditions of a facet for maximizing the coefficient of generalizability ...
Macromolecules, 1984
trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were... more trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were crystallized from solutions, mainly at a concentration of 1 g/100 cm3, by cooling directly from 100 OC to an (apparent) TC of -15 to +32 OC, by precooling to 0 "C, redissolving a t 35-45 "C, and crystallizing at Tc, and by cooling to 0 OC and heating to 10,20, or 30 "C. Most of the structures obtained were characterized, while suspended in the crystallization liquid, by interference contrast microscopy and with crossed polaroids; the crystalline fraction from the density and the crystal form from X-ray diffraction and differential scanning calorimetry were determined for the dry products. The morphology obtained by direct crystallization was dependent on molecular weight, crystallization temperature, and solvent, with a-and 0-hedrites (sheaves), a-and 0-spherulites, and 0-aggregates of cup-shaped lamellas being found. The precooling method yielded overgrown lamellas in most cases; however, more complex morphologies developed when the thermal history was changed. The density depended on molecular weight, concentration, and crystallization temperature. The crystallinity was mainly a function of crystal form and molecular weight. The equation of Tseng, Herman, Woodward, and Newman was used to explain the molecular weight dependence of the crystallinity at low M, and to calculate the average number of monomer units per fold and interlamellar traverse. Epoxidation of some TPI structures suspended in amyl acetate a t 0 "C was carried out. At high concentrations of the epoxidizing agent, m-chloroperbenzoic acid, the fraction epoxidized approached or exceeded the noncrystalline fraction as obtained from density measurement.
Multivariate Behavioral Research, 1975
ABSTRACT
trans-1,4-Polybutadiene (TPBD) fractions (Mu = 7000-36000) with a 1% cis content were crystallize... more trans-1,4-Polybutadiene (TPBD) fractions (Mu = 7000-36000) with a 1% cis content were crystallized from solution as a function of crystallization solvent, temperature, and concentration. The resulting structures were characterized quantitatively by using epoxidation in suspension followed by carbon-13 NMR measurement in solution, which yields the fraction reacted and the unreacted and reacted block lengths, A and B, respectively. Agreement between the fraction epoxidized and the noncrystalline fraction from density measurement was obtained. Evidence for the rejection of cis units from the trans-polybutadiene crystal core was found from the carbon-13 NMR studies. Although the amorphous (surface) fraction remains constant, A, equated to the number of monomer units per crystal traverse, and B, equated to the average number of monomer units per fold, increase with crystallization temperature. A and B remain constant with a change in morphology from single lamellar to multilamellar and with crystallization concentration from 0.05% to 5% w/v. The average number of TPBD units rejected from the crystal core when cis unit rejection occurs is estimated and the average length of a fold containing no cis unit is found to be 3-5 units.
Fourier transform infrared spectra were obtained for solution-crystallized samples of two polybut... more Fourier transform infrared spectra were obtained for solution-crystallized samples of two polybutadiene copolymers, one containing 10% cis-, 1,5% 1,2and 88,5% transand the other 1 070 cis-and 99% trans-polybutadiene. Measurements were made at room temperature, at temperatures above the crystal transition temperature, but below the melting temperature, and at temperatures above the melting temperature. Spectra for 100% crystalline samples were obtained by subtraction of the spectrum for the melt from that for the semicrystalline sample. Infrared spectra were also obtained for suspension epoxidized samples; these showed the presence of an unreacted crystal core and completely reacted lamellar surfaces.
A Simplified Conjoint Expected Risk (SCER: Holtgrave and Weber, 1993) model-based approach was us... more A Simplified Conjoint Expected Risk (SCER: Holtgrave and Weber, 1993) model-based approach was used to explore differences in the perceived risk of a variety of financial and health activities among Caucasians, African-Americans, Mexican-Americans, and Taiwanese-Americans. The SCER model postulates that the perceived risk of an activity is a function of five dimensions: the subjective probability of harm, benefit, and status quo, and the subjective expected harm and benefit. This model offers a framework in which to apply qualitative and quantitative approaches in order to identify and to assess the generality of ethnic group differences in the relative weight attached to probability and expected outcome information, the subjective valuation of probabilities and expected outcomes, and the perceived harms and benefits. Results demonstrated that the primary and most generalised locus of ethnic group perceived risk differences is the relative importance attached to probability and expe...
Risk Analysis, 2000
The simplified Conjoint Expected Risk (CER) model by Holtgrave and Weber posits that perceived ri... more The simplified Conjoint Expected Risk (CER) model by Holtgrave and Weber posits that perceived risk is a linear combination of the subjective judgments of the probabilities of harm, benefit, and status quo, and the expected harm and benefit of an activity. It modifies Luce and Weber's original CER model-that uses objective information to evaluate financial gambles-to accommodate activities such as health/technology activities where values of the model variables are subjective. If the simplified model is a valid modification of the original model, its performance should not be sensitive to the use of subjective information. However, because people may evaluate information differently when objective information is provided to them than when they generate information on their own, the performance of the simplified CER model may not be robust to the source of model-variable information. We compared the use of objective and subjective information, and results indicate that the estimates of the simplified CER model parameters and the proportion of variance in risk judgments accounted for by the model are similar under these two conditions. Thus, the simplified CER model is viable with activities for which harm and benefit information is subjective.
Macromolecules, 1983
... Susan Tseng and Arthur E. Woodward Department of Chemistry, City University of New York, City... more ... Susan Tseng and Arthur E. Woodward Department of Chemistry, City University of New York, City College, New York, New York 10031. ... These conditions were determined by measurement of 13C spin-lattice relaxation and nuclear Overhauser enhancement (NOE). ...
Macromolecules, 1988
trans-1,4-Polyisoprene structures in the a and @ crystalline forms with various morphologies were... more trans-1,4-Polyisoprene structures in the a and @ crystalline forms with various morphologies were prepared by using different crystallization procedures. The effects of molecular weight, crystallization temperature, and annealing treatment on the crystalline stem length and the noncrystalline traverse length were investigated by using epoxidation in suspension followed by carbon-13 solution NMR. Preliminary studies were carried out to determine the optimum conditions for quantitative reaction of the double bonds a t the lamellar surfaces. Results were obtained suggesting that for many liquids penetration of partially reacted lamellas can take place from the lateral surfaces; reactant concentration and time were also shown to be important and conditions were found that gave agreement between the fraction reacted and the noncrystalline fraction from infrared and density measurements. Interlamellar traverses were detected in multilamellar structures with the amount increasing with increasing molecular weight. The nature of chain folding in the trans-polydienes is discussed.
Macromolecules, 1984
We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the stu... more We report for the first time the application of solid-state carbon-13 NMR spectroscopy to the study of solution-grown polymer single crystals. Two samples of 1,4-trans-polybutadiene (it?,, = 9.8 x IO3 and 1.7 X lo4), grown from 0.01% heptane solution, were employed. With the appropriate use of magic-angle spinning and proton decoupling it is possible to measure chemical shifts, relaxation times, and nuclear Overhauser enhancements (NOE) of carbon nuclei in the crystal stems and amorphous regicms; the latter are assumed to consist exclusively of fold surfaces and cilia. Using dipolar decoupling but without magic-angle spinning, we examined the chemical shift anisotropy of the olefinic carbons. The powder pattern is asymmetric with a (ull -u33) of ca. 178 ppm. Using magic-angle spinning with dipolar decoupling but without lH-13C cross polarization, we have determined the fraction of crystallinity as 0.73 * 0.01 for both samples, in agreement with estimates from densities. Spin-lattice relaxation of the fold-surface carbons is shown to be predominantly dipolar. The less than maximal NOE values-ca. 2-are consistent with anisotropic chain motion. Both these findings and the chemical shifts of the fold-surface carbons agree with those reported by Jelinski et al." for bulk amorphous polybutadiene. The chemical shifts of the methylene carbons in the folds can be rationalized on the basis of the y-gauche shielding effect and the accepted rotational isomeric state model for unperturbed 1,4-trans-polybutadiene, but the upfield shift of the olefinic carbons is less than expected. It appears that the motions and conformations of the surface folds are similar to those of bulk polymer despite the constraints imposed on the folds by the requirement of adjacent reentry, established in a previous high-resolution study.1° Upon epoxidation with m-chloroperbenzoic acid, the folds give very broad carbon-13 resonances. Evidently, the introduction of oxirane rings immobilizes the chains sufficiently to prevent averaging of lH-13C dipolar interactions and 13C chemical shift anisotropies.
Macromolecules, 1984
trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were... more trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X lo3 to 2.5 X lo5 and Mw/M,, = 2.0-1.3 were crystallized from solutions, mainly at a concentration of 1 g/100 cm3, by cooling directly from 100 OC to an (apparent) TC of -15 to +32 OC, by precooling to 0 "C, redissolving a t 35-45 "C, and crystallizing at Tc, and by cooling to 0 OC and heating to 10,20, or 30 "C. Most of the structures obtained were characterized, while suspended in the crystallization liquid, by interference contrast microscopy and with crossed polaroids; the crystalline fraction from the density and the crystal form from X-ray diffraction and differential scanning calorimetry were determined for the dry products. The morphology obtained by direct crystallization was dependent on molecular weight, crystallization temperature, and solvent, with a-and 0-hedrites (sheaves), a-and 0-spherulites, and 0-aggregates of cup-shaped lamellas being found. The precooling method yielded overgrown lamellas in most cases; however, more complex morphologies developed when the thermal history was changed. The density depended on molecular weight, concentration, and crystallization temperature. The crystallinity was mainly a function of crystal form and molecular weight. The equation of Tseng, Herman, Woodward, and Newman was used to explain the molecular weight dependence of the crystallinity at low M, and to calculate the average number of monomer units per fold and interlamellar traverse. Epoxidation of some TPI structures suspended in amyl acetate a t 0 "C was carried out. At high concentrations of the epoxidizing agent, m-chloroperbenzoic acid, the fraction epoxidized approached or exceeded the noncrystalline fraction as obtained from density measurement.
Macromolecules, 1987
A statistical model based on the assumption of adjacent reentry in lamellas of trans-l,4polybutad... more A statistical model based on the assumption of adjacent reentry in lamellas of trans-l,4polybutadiene chains, containing randomly placed cis units, is developed for the calculation of crystallinity and of a NMR tetrad ratio in surface reacted specimens. In this treatment the chain ends and cis units appear at the lamellar surfaces and there are three types of chain folds: (i) those containing only trans-polybutadiene units and which have a constant length, (ii) those with interior cis Units with the same length for the all-trans fold, and (iii) those with cis units and accompanying trans units rejected from the crystal core, having a variable length. In this treatment the crystallinity and tetrad ratio are functions of (i) the cis content, (ii) the degree of polymerization, (iii) the crystal traverse length, and (iv) the all-trans-containing fold length, B'. Comparison of calculated with experimental values yields 4 f 1 for B'.
Macromolecules, 1988
Copolymers of trans-1,4-polyisoprene containing from 1 to 10% randomly placed epoxidized units we... more Copolymers of trans-1,4-polyisoprene containing from 1 to 10% randomly placed epoxidized units were crystallized from solution. The crystal form from infrared spectroscopy, the DSC melting endotherm(s), and the reacted and unreacted block lengths, as obtained by surface epoxidation in suspension followed by carbon-13 solution NMR, were determined. Small amounts of oxirane units (1-2%) have no significant effect on the melting endotherm or block lengths but do change the crystal form and the redissolution temperature. Evidence for incorporation of oxirane units in the crystal core is discussed.
Journal of the American Chemical Society, 1953
Page 1. Dec. 20, 1953 Low TEMPERATURE AUTOXIDATION OF HYDROCARBONS 6189 [CONTRIBUTION FROM THE PO... more Page 1. Dec. 20, 1953 Low TEMPERATURE AUTOXIDATION OF HYDROCARBONS 6189 [CONTRIBUTION FROM THE POLYMER RESEARCH INSTITUTE, POLYTECHNIC INSTITUTE OF BROOKLYN] Low Temperature Autoxidation of Hydrocarbons. ...