bluuebunny/crossref_metadata_2025 huggingface dataset:
Decreased viability of nitric oxide synthase double knockout mice
Authors: Tranguch Susanne , Huet‐Hudson Yvette
Published: April 2003

Nitric oxide acts as an important intracellular messenger in a variety of systems, including reproduction. Previous studies have shown the importance of nitric oxide in embryo development. NO is produced from l‐arginine by the enzyme, nitric oxide synthase (NOS), which has three isoforms: endothelial (NOS3), neural (NOS1), and inducible (NOS2). We hypothesize that, because of the importance of NOS in development, at least two NOS isoforms are required in order for normal embryo development to occur. Through the generation of NOS3/NOS2, NOS3/NOS1, and NOS2/NOS1 double knockout mice, we found that while litter size remains unchanged, the expected number of generated double knockout mice varies significantly from what would be predicted by Mendelian genetics. Estrous cycles were similar for both DKO and the wild‐type mice, and both groups were deemed fertile by their ability to mate with wild‐type (CD‐1) mice. Together, these results lead us to conclude that the lack of two NOS isoforms leads to a decreased viability in mice because of a developmental problem in the double knockout embryo. Mol. Reprod. Dev. 65: 175–179, 2003. © 2003 Wiley‐Liss, Inc.
Effects of cooling on meiotic spindle structure and chromosome alignment within in vitro matured porcine oocytes
Authors: Liu Rui‐Hua , Sun Qing‐Yuan , Li Yong‐Hai , Jiao Li‐Hong , Wang Wei‐Hua
Published: April 2003

Meiotic spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus–oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39°C, 5% CO2 in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4°C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the meiotic spindle and chromosome alignment or returned to maturation medium at 39°C for 2 hr for examination of spindle recovery. Most oocytes (65–71%) cooled to 24°C showed partially depolymerized spindles but 81–92% of oocytes cooled at 4°C did not have a spindle after cooling for 120 min. Quicker disassembly of spindles in the oocytes was observed at 4°C than at 24°C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited spindle recovery was observed in the oocytes cooled to both 4 and 24°C regardless of cooling time. The effect of cooling on the spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the meiotic spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled. Mol. Reprod. Dev. 65: 212–218, 2003. © 2003 Wiley‐Liss, Inc.
Effects of exogenous hexoses on bovine in vitro fertilized and cloned embryo development: Improved blastocyst formation after glucose replacement with fructose in a serum‐free culture medium
Authors: Kwun Jean , Chang Kyunghee , Lim Jeongmook , Lee Eunsong , Lee Byeongchun , Kang Sungkeun , Hwang Woosuk
Published: April 2003

To evaluate the embryotrophic role of three hexoses (glucose, fructose, and galactose), bovine embryos derived from somatic cell nuclear transfer (SCNT) or in vitro‐fertilization (IVF) were cultured in a modified synthetic oviductal fluid (mSOF), which contained either glucose (1.5 or 5.6 mM), fructose (1.5 or 5.6 mM), or galactose (1.5 or 5.6 mM). Compared to 1.5 mM glucose, use of 1.5 mM fructose significantly enhanced blastocyst formation in both SCNT (23 vs. 33%) and IVF embryos (26 vs. 34%), while 5.6 mM fructose did not improve blastocyst formation. Using 1.5 mM galactose did not improve blastocyst formation in SCNT embryos (22 vs. 23%), whereas it significantly inhibited blastocyst formation in IVF embryos (26 vs. 0%). In both SCNT and IVF embryos, 5.6 mM glucose or galactose significantly inhibited embryo development. In a second experiment, in glucose‐free mSOF, fructose at concentrations of 0.75, 1.5, 3.0, or 5.6 mM was able to support to morula (32–42 vs. 12%) and blastocyst formation (30–38 vs. 12%) compared to 0 mM fructose. In Experiment 3, addition of fructose (1.5, 3.0, or 5.6 mM) to mSOF containing 1.5 mM glucose did not further promote blastocyst formation in SCNT embryos compared with replacement with 1.5 mM fructose only. Replacement of glucose with 1.5 mM fructose significantly increased total blastomeres (143 vs. 123 cells) and trophectodermal (TE) cells (116 vs. 94 cells) and decreased inner cell mass (ICM) to TE cell ratio (0.24 vs. 0.31) in blastocysts, compared to 1.5 mM glucose. The combined addition of 1.5 mM fructose and glucose significantly increased ICM cell number (36.7 cells) and ICM/TE ratio (0.46). In conclusion, fructose might be a more efficient energy substrate than glucose for producing large number of transferable blastocysts derived from SCNT. Mol. Reprod. Dev. 65: 167–174, 2003. © 2003 Wiley‐Liss, Inc.
Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 T
Authors: Mildner Toralf , Trampel Robert , Möller Harald E. , Schäfer Andreas , Wiggins Christopher J. , Norris David G.
Published: April 2003

Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin‐echo echo‐planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger‐tapping task. Signal differences between the condition of finger tapping and the resting state were between −0.5% and −1.1 % among the subjects. The imaging protocol included a long post‐label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791–795, 2003. © 2003 Wiley‐Liss, Inc.
Comparison of temporal filtering methods for dynamic contrast MRI myocardial perfusion studies
Authors: Di Bella E.V.R. , Wu Y.J. , Alexander A.L. , Parker D.L. , Green D. , McGann C.J.
Published: April 2003

Dynamic contrast myocardial perfusion studies may benefit from methods that speed up the acquisition. Unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD), and a similar linear interpolation method have been shown to be effective at reducing the number of phase encodes needed for cardiac wall motion studies by using interleaved sampling and temporal filtering. Here such methods are evaluated in cardiac dynamic contrast studies, with particular regard to the effects of the choice of filter and the interframe motion. Four different filters were evaluated using a motion‐free canine study. Full k‐space was acquired and then downsampled to allow for a measure of truth. The different filters gave nearly equivalent images and quantitative flow estimates compared to full k‐space. The effect of respiratory motion on these schemes was graphically depicted, and the performance of the four temporal filters was evaluated in seven human subjects with respiratory motion present. The four filters provided images of similar quality. However, none of the filters were effective at eliminating motion artifacts. Motion registration methods or motion‐free acquisitions may be necessary to make these reduced FOV approaches clinically useful. Magn Reson Med 49:895–902, 2003. © 2003 Wiley‐Liss, Inc.
Hemodynamic segmentation of MR brain perfusion images using independent component analysis, thresholding, and Bayesian estimation
Authors: Kao Yi‐Hsuan , Guo Wan‐Yuo , Wu Yu‐Te , Liu Kuo‐Ching , Chai Wen‐Yen , Lin Chiao‐Yuan , Hwang Yi‐Shuan , Jy‐Kang Liou Adrain , Wu Hsiu‐Mei , Cheng Hui‐Cheng , Yeh Tzu‐Chen , Hsieh Jen‐Chuen , Mu Huo Teng Michael
Published: April 2003

Dynamic‐susceptibility‐contrast MR perfusion imaging is a widely used imaging tool for in vivo study of cerebral blood perfusion. However, visualization of different hemodynamic compartments is less investigated. In this work, independent component analysis, thresholding, and Bayesian estimation were used to concurrently segment different tissues, i.e., artery, gray matter, white matter, vein and sinus, choroid plexus, and cerebral spinal fluid, with corresponding signal–time curves on perfusion images of five normal volunteers. Based on the spatiotemporal hemodynamics, sequential passages and microcirculation of contrast‐agent particles in these tissues were decomposed and analyzed. Late and multiphasic perfusion, indicating the presence of contrast agents, was observed in the choroid plexus and the cerebral spinal fluid. An arterial input function was modeled using the concentration–time curve of the arterial area on the same slice, rather than remote slices, for the deconvolution calculation of relative cerebral blood flow. Magn Reson Med 49:885–894, 2003. © 2003 Wiley‐Liss, Inc.
Artifact reduction in true‐FISP imaging of the coronary arteries by adjusting imaging frequency
Authors: Deshpande Vibhas S. , Shea Steven M. , Li Debiao
Published: April 2003

The presence of resonance frequency offsets often causes artifacts in images acquired with true fast imaging with steady‐state precession (true‐FISP). One source of resonance offsets is a suboptimal setting of the synthesizer frequency. The goal of this work was to demonstrate that shifting the synthesizer frequency could minimize the off‐resonance related image artifacts in true‐FISP. A simple scouting method was developed to estimate the optimal synthesizer frequency for the volume of interest (VOI). To improve fat suppression, a similar scouting method was also developed to determine the optimal frequency offset for the fat saturation pulse. Coronary artery imaging was performed in healthy subjects using a 3D true‐FISP sequence to validate the effectiveness of the frequency corrections. Substantial reduction in image artifacts and improvement in fat suppression were observed by using the water and fat frequencies estimated by the scouting scans. Frequency shifting is a useful and practical method for improving coronary artery imaging using true‐FISP. Magn Reson Med 49:803–809, 2003. © 2003 Wiley‐Liss, Inc.
Localized proton MRS of cerebral metabolite profiles in different mouse strains
Authors: Schwarcz Attila , Natt Oliver , Watanabe Takashi , Boretius Susann , Frahm Jens , Michaelis Thomas
Published: April 2003

Localized proton MR spectroscopy (MRS) was used to quantify cerebral metabolite concentrations in NMRI (n = 8), BALB/c (n = 7), and C57BL/6 (n = 8) mice in vivo and 1 hr after global irreversible ischemia (2.35 T, STEAM, TR/TE/TM = 6000/20/10 ms, 4 × 3 × 4 mm3 volume, corrections for cerebrospinal fluid). Anatomical MRI and proton MRS revealed significant differences of the C57BL/6 strain in comparison with both BALB/c and NMRI mice. While MRI volumetry yielded larger ventricular spaces of the C57BL/6 strain, proton MRS resulted in elevated concentrations of N‐acetylaspartate (tNAA), creatine and phosphocreatine (tCr), choline‐containing compounds (Cho), glucose (Glc), and lactate (Lac) relative to BALB/c mice and elevated Glc relative to NMRI mice. Apart from the expected decrease of Glc and increase of Lac 1 hr post mortem, C57BL/6 mice presented with significant reductions of tNAA, tCr, and Cho, whereas these metabolites remained unchanged in BALB/c and NMRI mice. The results support the hypothesis that the more pronounced vulnerability of C57BL/6 mice to brain ischemia is linked to strain‐dependent differences of the cerebral energy metabolism. Magn Reson Med 49:822–827, 2003. © 2003 Wiley‐Liss, Inc.
Dynamic, contrast‐enhanced perfusion MRI in mouse gliomas: Correlation with histopathology
Authors: Cha Soonmee , Johnson Glyn , Wadghiri Youssef Zaim , Jin Olivier , Babb Jim , Zagzag David , Turnbull Daniel H.
Published: April 2003

The aim of this study was to develop an MRI protocol to evaluate the growth and vascularity of implanted GL261 mouse gliomas on a 7T microimaging system. Both conventional T1‐ and T2‐weighted imaging and dynamic, contrast‐enhanced T2*‐weighted imaging were performed on 34 mice at different stages of tumor development. MRI measurements of relative cerebral blood volume (rCBV) were compared to histological assessments of microvascular density (MVD). Enhancement on postcontrast T1‐weighted images was compared to histological assessments of Evan's blue extravasation. Conventional T2‐weighted and postcontrast T1‐weighted images demonstrated tumor growth characteristics consistent with previous descriptions of GL261 glioma. Furthermore, measurements of rCBV from MRI data were in good agreement with histological measurements of MVD from the same tumors. Postcontrast enhancement on T1‐weighted images was observed at all stages of GL261 glioma progression, even before evidence of angiogenesis, indicating that the mechanism of conventional contrast enhancement in MRI does not require neovascularization. These results provide quantitative support for MRI approaches currently used to assess human brain tumors, and form the basis for future studies of angiogenesis in genetically engineered mouse brain tumor models. Magn Reson Med 49:848–855, 2003. © 2003 Wiley‐Liss, Inc.
SNR improvement for multiinjection time‐resolved high‐resolution CE‐MRA of the peripheral vasculature
Authors: Du J. , Carroll T.J. , Block W.F. , Fain S.B. , Korosec F.R. , Grist T.M. , Mistretta C.A.
Published: April 2003

Peripheral MR angiography (MRA) should ideally provide images over a large field of view with high spatial resolution and adequate temporal resolution to accommodate differences in regional filling times. Image subtraction is usually used to remove background signals. In examination protocols involving multiple injections at multiple sites, previously injected contrast present in the mask image provides a substantial decrease in the subtraction image signal. Bolus chase methods avoid this problem but provide limited time for acquisition of high‐resolution images at each station. We present here a technique applied to peripheral angiography that provides high spatial and temporal resolution while maintaining high SNR in multiple injection examinations. Undersampled projection imaging was used to increase spatial resolution relative to a previously reported technique using a Cartesian acquisition technique. Late acquisition of high spatial frequencies and temporal matched‐filtering were used to increase spatial resolution and SNR, respectively. Temporal correlation analysis was applied to permit multistation examinations without mask subtraction, thus providing an additional gain in SNR relative to multistation subtraction methods. Quantitative analysis is provided to evaluate the signal and noise behavior in the matched‐filtering process due to multiinjection and mask subtraction. Magn Reson Med 49:909–917, 2003. © 2003 Wiley‐Liss, Inc.
Water diffusion measurements in perfused human hippocampal slices undergoing tonicity changes
Authors: Shepherd Timothy M. , Wirth Edward D. , Thelwall Peter E. , Chen Huan‐Xin , Roper Steven N. , Blackband Stephen J.
Published: April 2003

Diffusion MRI has the potential to probe the compartmental origins of MR signals acquired from human nervous tissue. However, current experiments in human subjects require long diffusion times, which may confound data interpretation due to the effects of compartmental exchange. To investigate human nervous tissue at shorter diffusion times, and to determine the relevance of previous diffusion studies in rat hippocampal slices, water diffusion in 20 perfused human hippocampal slices was measured using a wide‐bore 17.6‐T magnet equipped with 1000‐mT/m gradients. These slices were procured from five patients undergoing temporal lobectomy for epilepsy. Tissue viability was confirmed with electrophysiological measurements. Diffusion‐weighted water signal attenuation in the slices was well‐described by a biexponential function (R2 > 0.99). The mean diffusion parameters for slices before osmotic perturbation were 0.686 ± 0.082 for the fraction of fast diffusing water (Ffast), 1.22 ± 0.22 × 10−3 mm2/s for the fast apparent diffusion coefficient (ADC), and 0.06 ± 0.02 × 10−3 mm2/s for the slow ADC. Slice perturbations with 20% hypotonic and 20% hypertonic artificial cerebrospinal fluid led to changes in Ffast of −8.2% and +10.1%, respectively (ANOVA, P < 0.001). These data agree with previous diffusion studies of rat brain slices and human brain in vivo, and should aid the development of working models of water diffusion in nervous tissue, and thus increase the clinical utility of diffusion MRI. Magn Reson Med 49:856–863, 2003. © 2003 Wiley‐Liss, Inc.
Separating arterial and venous components from 3D dynamic contrast‐enhanced MRI studies using factor analysis
Authors: Martel Anne L. , Fraser Doug , Delay G. Steve , Morgan Paul S. , Moody Alan R.
Published: April 2003

Dynamic contrast‐enhanced MRI has been used extensively for angiography but in order to generate separate arterial and venous images some form of postprocessing is required. This typically involves the subtraction of one image in a dynamic sequence from another in order to suppress unwanted signal; however, this also has the effect of decreasing the signal‐to‐noise ratio (SNR) of the image. In this study, factor analysis, a technique related to eigenimage filtering, is used to separate arterial and venous components from dynamic contrast‐enhanced images of the legs acquired with a temporal resolution of 30 sec. The SNR of the venous and arterial images extracted from a series of 20 patients using conventional single subtraction, a double subtraction method, and factor analysis were compared. Results show that the use of factor analysis improved the SNR in the venous images by a factor of 2.3 compared with the use of simple subtraction. A subjective comparison of the maximum intensity projection images generated from the venous images was also carried out and showed a significant preference for those generated using factor analysis over those generated using other subtraction methods. Magn Reson Med 49:928–933, 2003. © 2003 Wiley‐Liss, Inc.
Conveners as champions of collaboration in the public sector: a case from South Africa
Authors: Dorado Silvia , Vaz Peter
Published: April 2003

This article analyses the role of conveners in facilitating interorganisational collaboration. Consistent with previous research, the article shows that conveners help overcome the obstacles frequent in interorganisational collaboration processes. It also illustrates further how their effectiveness depends on their credibility among the partners, their familiarity with the collaborative project and their being perceived as unbiased intermediaries. Most interestingly, the article advances our knowledge on conveners by suggesting that their behaviour is consistent with that common among ‘champions’ of innovation. They are likely to assume a leadership role and use influence politics, such as salesmanship, personal appeal and persuasion. These findings build on a case study of successful collaboration between two government agencies in South Africa. We believe, however, that the findings are likely to apply to other types of organisation, private and voluntary, and to other country contexts. Copyright © 2003 John Wiley & Sons, Ltd.
Fighting fiscal corruption: lessons from the Tanzania Revenue Authority
Authors: Fjeldstad Odd‐Helge
Published: April 2003

Over the last decade, several African countries have undertaken comprehensive reforms of their tax administrations to increase revenue and curb corruption. This article examines recent experiences in the fight against corruption in the Tanzania Revenue Authority (TRA). Two lessons of broader relevance are highlighted. Firstly, even with relatively high wages and good working conditions, corruption may continue to thrive. In a situation where there is high demand for corrupt services, it is unrealistic to provide tax officers with pay rates that can compensate for the amount gained through bribery. Without extensive and effective monitoring, wage increases may produce not only a highly paid, but also a highly corrupt tax administration. Secondly, hiring and firing procedures may lead to more corruption. Corrupt tax officers often operate in networks, which also include external actors. These corruption networks seem to have been strengthened because many of those fired were recruited to the private sector as ‘tax experts’. This partly explains why the positive process experienced in the initial phase of the new revenue authority was later reversed. Copyright © 2003 John Wiley & Sons, Ltd.
Mechanism of vinyl polymerizations. VIII.1 Introduction of foreign end groups
Authors: Price Charles C. , Read David H.
Published: April 2003

Results are reported of experiments designed to delineate more clearly the action of retarders and chain transfer agents and to place different labeled end groups at either end of polystyrene molecules.
The mechanism of reinforcement. II
Authors: Goldfinger George
Published: April 2003

Further experimental evidence is given which indicates that, when a dilute solution of GR‐S is mixed with carbon black, certain fractions of the rubber are preferentially adsorbed by the black. After removal of the carbon black and the adsorbed fractions by centrifuging, the “treated” GR‐S is obtained by precipitation from the solution. Samples compounded as GR‐S gum stock show increasing modulus with increasing amounts of carbon black used for adsorption treatment. However, when the GR‐S thus treated is compounded with carbon black, then the effect is reversed. The more black used in the treatment and the higher the modulus of the gum stock, the lower the modulus of loaded stock.
Intramolecular reactions in vinyl polymers as a means of investigation of the propagation step
Authors: Merz E. , Alfrey T. , Goldfinger G.
Published: April 2003

The Flory‐Wall expressions for the fraction of substituents remaining on a vinyl copolymer, when substituents are removed at random from adjacent 1,3 positions, are extended to the case of nonrandom copolymerization. A copolymer composition equation is derived for the case in which the type of monomer preceding the active freeradical chain end affects the propagation reaction. The distribution of lengths of sequences in copolymers is discussed.
Preparation, purification, and polymerization of diethyl silicon dichloride
Authors: Alfrey Turner , Honn Francis J. , Mark H.
Published: April 2003

Diethyl silicon dichloride was prepared by a Grignard synthesis and purified highly. The material in various stages of purification was hydrolyzed and then polymerized. The properties of the hydrolyzate and of the final polymer depended markedly upon the degree of purification of the dichloride. The reaction of diethylsilicanediol with phosphorous pentoxide was also studied; the predominating reaction appears to involve entrance of the pentoxide into the polymeric structure, rather than a simple acceleration of the polycondensation reaction by the removal of water.
Polymerization of olefins and diolefins in suspension and emulsion. Part I.
Authors: Hohenstein W. P. , Mark H.
Published: April 2003

This and a following article review the literature from 1910–1945 on polymerization of olefins and diolefins in suspension and emulsion, and present a number of new measurements not published to date. The subject is considered mainly from the point of view of scientific information on the mechanism of polymerization in aqueous suspensions and emulsions, but brief mention is also made of the more important disclosures in the patent literature. The new data presented in this article refer to (1) initial rates of polymerization of styrene, methyl methacrylate, vinyl acetate and acrylonitrile in aqueous suspensions and in soap emulsions as a function of catalyst concentration, temperature, and soap concentration; (2) influence of water‐soluble activators, such as sodium bisulfite; (3) influence of initial size of monomer droplets on initial rates of monomer consumption; (4) study, with the aid of the electron microscope, of size of monomer droplets and polymer particles throughout polymerization; and (5) a few experiments on side reactions in the domain of higher conversions. No attempt is made in this paper to review and appraise the very large number of recent patents (from about 1930 on), which protect special procedures on the use of various promoting, regulating, or modifying ingredients. A complete digest of this practice does not exist at present, but reference may be made to the excellent chapter on emulsion polymerization in the book of Talalay and Magat (55), to the very valuable compilation of patents by Hosch in “India Rubber World” (27), and to the enumeration of a selected number of patents in the book of Scheiber (50) on pages 210–213.
Density of cellulose fibers. II. Density and refractivity of model filaments
Authors: Hermans P. H. , Hermans J. J. , Vermaas D.
Published: April 2003

Accurate determinations of the density and refractive power of various types of model filaments prepared from viscose in the bone‐dry state were made. The molecular refraction, according to the formula of Gladstone and Dale, was calculated and shown to correspond within three parts per thousand with the refraction calculated from atomic refractions. It is concluded that the liquid used for the density determinations (mixtures of carbon tetrachloride and nitrobenzene) does not penetrate into the fiber substance. The technique of the experiments is described in detail. The immersion liquids used in the optical measurements were standardized mixtures of butyl stearate and tricresyl phosphate; contamination with moisture during the measurements was definitely excluded.
Spectrophotometric determination of the styrene content of butadiene–styrene copolymers
Authors: Meehan E. J.
Published: April 2003

The ultraviolet absorption of polystyrene, with maximum absorption at 262 mμ, is due to the presence of phenyl residues in the polymer. The specific extinction coefficient is constant, i.e., independent of the molecular weight of the polymer. This shows that the extinction of the phenyl residues is additive. On the basis of this fact, it is shown that the styrene content of a butadiene–styrene copolymer (such as GR‐S rubber) can be determined by ultraviolet spectrophotometry. The relative precision of the determination is about 1%, the probable relative accuracy is about 3%.
The photochemical decomposition of cellulose acetate–butyrate
Authors: Tichenor R. L.
Published: April 2003

The chief result of irradiation of cellulose acetate–butyrate with ultraviolet light is cleavage of the cellulose chains so that the average molecular weight is lowered. The exposed material dissolves more slowly in common solvents than the unexposed. The acyl content and carbon and hydrogen contents are not altered appreciably. The rate of the reaction is independent of the type of common mineral impurities, the concentration of expected decomposition products, such as acetic and butyric acids, and the molecular weight of the cellulose ester. Ultraviolet light is necessary for appreciable reaction. Wave lengths shorter than 3500 Å. are most effective; longer wave lenghts are much less active.
Comparison of ultraviolet absorption and chlorine analysis methods for composition of butadiene–p‐chlorostyrene copolymers
Authors: Meehan E. J. , Parks T. D. , Laitinen H. A.
Published: April 2003

A comparison has been made of the ultraviolet spectrophotometric and chlorine analysis methods for the composition of copolymers of butadiene and p‐chlorostyrene. The results of the two methods are in good agreement.
Use of density‐gradient tube in the study of high polymers
Authors: Boyer R. F. , Spencer R. S. , Wiley R. M.
Published: April 2003

The density‐gradient tube is a special glass vessel in which a vertical linear density gradient of almost any desired magnitude can be maintained in a stable condition for prolonged periods by using liquids or solutions of the proper density. This article describes the application of such a device to three typical problems appearing in the field of high polymers: crystallization‐rate data, inhomogeneities in composition of copolymers, and rates of polymerization. Possible application to still other problems is indicated.
Technique of electron‐microscope investigation of fiber surfaces
Authors: Kern Stanley F.
Published: April 2003

The technique of obtaining polystyrene silica replicas from surfaces and cross sections of fibers is described and electron micrographs obtained from replicas of several fibers are shown.
Sodium‐catalyzed copolymerization of 1,3‐butadiene and styrene
Authors: Marvel C. S. , Bailey W. J. , Inskeep G. E.
Published: April 2003

Butadiene and styrene have been copolymerized by the use of sodium sand as a catalyst. The copolymers containing 75 parts of butadiene and 25 parts of styrene and made at 30° and 50° are soluble in benzene and have intrinsic viscosities ranging from 2.5 to 7.5. The copolymers has a very nearly constant composition throughout the course of the polymerization. The amount of butadiene which has entered the chain by 1,2 addition is greater than in the case of the emulsion copolymer.
β‐Aminoethoxyl‐ and β‐cyanoethoxylcellulose acetates
Authors: Gardner Thomas S.
Published: April 2003

Mixed cellulose acetate‐ethers were prepared which contain basic‐type nitrogen groups whose films were dyed by xylene brilliant blue. β‐Aminoethoxylcellulose acetate was prepared from cellulose diacetate and yarn‐type cellulose acetate–propionate using ethyleneimine. β‐Cyanoethoxylcellulose acetate was prepared from β‐cyanoethoxylcellulose and from cellulose acetate using acrylonitrile with an organic base as catalyst. The solubilities of the mixed ether–esters containing basic type nitrogen groups were less than those of cellulose esters and ethers of comparable degrees of substitution.
Composition of butadiene–styrene copolymers prepared by emulsion polymerization
Authors: Meehan E. J.
Published: April 2003

Experimental data are presented on the monomer composition of copolymers of butadiene and styrene prepared by emulsion polymerization at 50°C. The composition of the copolymers is shown to be unaffected by variations in the amount of emulsifier, of mercaptan, and of the nature of the water‐soluble polymerization catalyst. The composition of the copolymers formed from a charge containing 25% styrene (by wt.) can be represented accurately over the entire conversion range by the approximate theory according to which each monomer disappears by a first order reaction with the growing chain of the polymer, without taking into account the fact that the end of the growing chain to which the monomer adds may be a radical derived from either of the two monomer molecules. If the ratio of monomers in the charge is varied within wide limits, however, it is found that the simple theory is not adequate and it is necessary to consider that the chain may end with different radicals. The analysis of the experimental data shows that a butadiene molecule adds more rapidly than a styrene molecule to a radical derived either from a butadience or a styrene molecule.
Dependence of the average transversal on the longitudinal dimensions of statistical coils formed by chain molecules
Authors: Kuhn Werner
Published: April 2003

The transversal dimension of the statistical coil formed by a long‐chain molecule in solution or in bulk rubber is independent of the longitudinal dimension, h1, of the coil as long as h1 is small compared with the length of the stretched molecule. On the other hand, the lateral dimension of a coil whose longitudinal vector, h1, is oriented in the direction of stretch undergoes a forced contraction during the deformation of bulk rubber. The forced contraction of the transversal dimension is therefore supplying an extra contribution to the entropy change. Its amount has been estimated in earlier work and it influences the numerical factor occurring in the formula connecting the strain‐stretch relation for rubber with the molecular weight of the net fragments.
Deformation mechanism of cellulose gels. II. Course of crystallite orientation compared to that required by Kratky's theory
Authors: Hermans P. H. , Hermans J. J. , Vermaas D. , Weidinger A.
Published: April 2003

The paper offers a verification by x‐ray experiments of Kratky's theory of affined transformation (affine Raumverzerrung), aiming at an explanation of the mechanism of deformation of swollen cellulose gels upon stretching. Isotropic model filaments of various degrees of swelling were stretched to various extents and x‐ray photographs were then taken. Following Kratky, the intensity distribution along the sickles of two paratropic planes of the ribbon‐shaped crystallites, the lamellar plane, A0 and the A3 plane (perpendicular to the latter) were measured and the average orientation, expressed in terms of the orientation factor, fx, was calculated. The superposition of the (021) interference on that of the A3 sickle, which had been neglected by Kratky, was accounted for. The experimental results are in conformity with certain characteristic features of the theory; (a) the orientation of the A0 planes advances more rapidly than that of the A3 planes; (b) regardless of the initial degree of swelling of the isotropic filament, the average orientation is actually a univocal function of the elongation, va. On the other hand, the rate of orientation appears to be much greater than that required by theory; the average orientation, expressed in terms of the orientation factor, increases almost twice as rapidly. It is shown, moreover, that, apart from low degrees of orientation, Kratky's theory fails to explain the velocity function of the relative rotation of the crystallites, as derived from the experimental data according to a procedure proposed by Kratky. It is concluded that further work is required to elucidate the mechanism of deformation.
Nature of the carbonyl groups in polyvinyl alcohol
Authors: Clarke John T. , Blout Elkan R.
Published: April 2003

Measurements of the viscosity of polyvinyl alcohol solutions may be correlated with the chemical nature of the polymer. In particular it is shown that polyvinyl alcohol contains carbonyl groups in the polymer chain, which are to some extent present as ketols. The presence of these keto groups has been demonstrated by a combination of spectrophotometric and chemical techniques. The carbonyl groups appear to be randomly distributed along the polymer chain and also seem to be independent of chain length. The presence of keto groups along the chain allows an explanation for the behavior of aqueous polyvinyl alcohol solutions with acid or alkali.
The Baker‐Philippoff equation for cellulose acetate solutions
Authors: Riley Jesse L.
Published: April 2003

By suitable alteration of the exponent the fit of viscosity‐concentration data by a Philippoff type equation may be substantially improved. For a series of cellulose acetate solutions the exponent of best fit appears to be related to the physical properties and chemical type of the solvent.
Molecular weight averages obtained from sedimentation velocity and diffusion measurements
Authors: Singer Seymour
Published: April 2003

In using the velocity ultracentrifuge in conjunction with free diffusion measurements for the determination of molecular weights of polymolecular systems, it is desirable to know what average molecular weights are obtainable. These average values are not simple moments of the molecular weight frequency curve, but depend on the methods of experimental observation, and on the hydrodynamic character of the molecules in solution. Most often, however, the average molecular weight falls between the number and weight‐average values.
Dependence of solvation on particle shape
Authors: Jirgensons B.
Published: April 2003

The relationships which exist between the solvation and shape of colloid particles, as well as between solvation and viscosity, are discussed. From the most important experiments on these subjects the following conclusions may be drawn. Solvation is dependent on the size and shape of the particles and on the chemical relationship of the dispersion medium to the dispersed portion. True or chemical solvation is generally very small and there is no reason to speak of a thick and tightly bound solvent layer. The solvation of compactly formed particles of spherocolloids is greater, the smaller the particles (all other conditions being equal). Solvation is greater, the more loosely the particles are formed (for dispersion mediums having similar chemical properties and for similar dispersed or dissolved substances). Solvation increases when a corpuscular particle is transformed into a rodlike or threadlike particle; the viscosity also increases; if the threads are further broken down into smaller fragments, then the viscosity decreases, but a further increase in the chemical solvationis supposed to occur. The stability of many lyophilic sols, especially the proteins, depends very little on the solvation; it is mainly dependent on the chemical characteristics of the atomic groups which are found on the surfaces of the particles; the least stability is found for surfaces which contain heteropolar groups—that is, surfaces which have the same number of positive and negative ions.
Phase separation in polymer solution
Authors: Dobry A. , Boyer‐Kawenoki F.
Published: April 2003

The phase separation in solutions of high polymers in the same solvent (technically known as incompatibility) has been studied for fourteen high polymers (cellulose, vinyl, and acrylic derivatives) dissolved in thirteen solvents. The influence of solvent, concentration, molecular weight and constitution of the macromolecules has been studied for 78 mixtures: the results are represented in triangular diagrams. Incompatibility appears to be the normal situation, compatibility the exception. Moreover, in cetain cases the exception may be only apparent. Phase separation is discussed in its relation to osmotic pressure, solubility, and the isomorphism of the molecules. Phase separation furnishes new means—useful at leat for technical research—of measuring the molecular weight of macromolecules. It is a simple and rapid procedure.
Use of perbenzoic acid in analysis of unsaturated compounds. III. Results of determinations of external double bonds in synthetic rubbers
Authors: Kolthoff I. M. , Lee Thomas S. , Mairs Mary Anne
Published: April 2003

Emulsion polybutadiene and emulsion copolymers of butadiene and styrene (e.g., GR‐S) contain about 20% external double bonds. A systematic study has been made of the effects of temperature, type of “catalyst,” percentage conversion, microgel formation, and varying styrene content of emulsion copolymers of butadiene and styrene. None of these variables affects the amount of external double bonds. Copolymers of butadiene with styrene and a small amount of acrylonitrile, and of butadiene with various monochlorostyrenes and dichlorostyrene, all prepared by emulsion polymerization, were found to contain the same amount of external double bonds. Emulsion polyisoprene and the emulsion copolymers of isoprene and styrene (75:25) were found to contain only 13 and 5%, respectively, external double bonds. Polybutadiene, butadiene—styrene copolymer, and polyisoprene, all prepared by sodium—catalyzed, bulk polymerization at 50°C., contain 50–60% external double bonds. The amount of external double bonds in sodium polybutadiene is strongly dependent on temperature of polymerization. More external double bonds are formed at low temperatures than at high temperatures. The amount of external double bonds in sodium butadiene—styrene copolymer and in sodium polyisoprene is nearly independent of temperature in the range 30–50°C. A sample of sodium polyisoprene was found to contain 36% internal double bonds and 64°C external double bonds. From an analysis of the reaction—rate curve it was concluded that approximately 40% (absolute percentage) of the external double bonds were formed by 3,4 addition and 24% by 1,2 addition. The rates of reaction of the cis—and trans—forms of natural rubber are very nearly the same, the cis—form reacting slightly more rapidly.
Kinetic treatment of emulsion polymerization
Authors: Corrin M. L.
Published: April 2003

The kinetics of the emulsion polymerization of styrene are developed on the basis of the Harkins' theory of reaction loci. Only that portion of the reaction is considered in which essentially no polymer nuclei are formed. Agreement is obtained between experiment and theory when the reaction in the monomer‐polymer particle is considered three‐halves order with respect to monomer. This treatment is further substantiated by the fact that the concentration of monomer in the polymer, when a separate monomer phase exists, is correctly predicted by the kinetic theory. The activation energy for the polymerization of styrene in the monomer‐polymer particle is calculated as 22,600 calories per mole. A dilatometer for the precise determination of monomer conversion rates in emulsion polymerization is described.
Heat conduction and molecular structure in rubberlike polymers
Authors: Rehner John
Published: April 2003

In this paper experimentally determined values are reported for the thermal diffusivity (k) of various rubberlike polymers. Corresponding values of the thermal conductivity (W) can be computed from the well‐known relationship, W = kpcp, where p and cp denote the density and specific heat at constant pressure of the composition. Measurements were made on (a) pure gum stocks prepared with natural rubber, Butyl (GR‐I), Perbunan 18, Perbunan 26, Perbunan 35, Buna S (GR‐S), polybutadiene, neoprene GN, polyisoprene, Silastic 160, and Silastic 180; (b) pure gum stocks of the first five rubbers listed under (a) containing in addition 20 parts of a hydrocarbon softener (Bardol), based on 100 parts by weight of the polymer; and (c) the Bardol stocks containing in addition 54 parts of carbon black (Kosmobile 66). From measurements of the rate of change of temperature within a rubber sphere suddenly subjected to a change in its surface temperature, it was found possible to determine the dependence of k on temperature. A satisfactory definition of the “mean” temperature of a sphere under these conditions is described. In a discussion of the effect of chemical composition and structure on heat conduction, the bearing of hindered rotation, cross linking and branching and interatomic bond strength on the results is pointed out. Values are derived for certain other properties of some of the polymers, including their characteristic Debye temperatures, specific heats at constant volume, flexibility of the main valence chains, compressibilities, and sound velocities.
Polymeric amides from diamines and dibasic acids
Authors: Coffman D. D. , Berchet G. J. , Peterson W. R. , Spanagel E. W.
Published: April 2003

Methods for the preparation of fiber‐forming polymeric amides from polymethylene diamines and polymethylene dicarboxylic acids, and the stabilization of these polymers against viscosity changes, have been described. The variation in physical properties, particularly melting points, of the polymeric amides with increasing chain length of the components has been discussed.
Recent ultracentrifugal investigations on cellulose and cellulose derivatives
Authors: Jullander Ingvar
Published: April 2003

A review is given of physicochemical studies on cellulose and cellulose derivatives made during the years of World War II at the Institute of Physical Chemistry, Uppsala, Sweden. Emphasis has been laid on the principles of the subject and the review deals essentially with some investigations on nitrocellulose by the present author. An outline of the problems of the cellulose chemistry of today serves as an introduction. The principles of molecular weight determinations from Svedberg's equation are briefly mentioned, and the difficulties in the extrapolation of sedimentation constants to zero concentration are discussed. The problem of what sort of average molecular weight is obtained from Svedberg's equation is treated subsequently and methods for determination of distributions from combinations of osmotic and sedimentation experiments described. A table comparing five different sorts of average molecular weights for a numbe of nitrocelluloses is discussed.
Rapid method for sampling latices in bottle polymerizations in which positive gage pressure is maintained in bottle by a monomer
Authors: Williams D. E. , Johnson W. F.
Published: April 2003

A procedure is described for the rapid sampling of latex during emulsion bottle polymerization. The equipment used consists of a hypodermic needle with holder, an adapter, a balance sensitive to one milligram, and dishes for determination of total solids. The equipment is used in connection with Paracon or Buna N self‐sealing caps. The procedure is very simple, rapid, and may be used in obtaining samples for total solids. mercaptan analysis, or gel and viscosity determinations.
Solubility, diffusion, and permeation of gases in gutta‐percha
Authors: Van Amerongen G. J.
Published: April 2003

The permeability of vulcanized gutta‐percha membranes to gases was determined in relation to the rate of diffusion and solubility. The measurements, as functions of temperature, with four gases were taken below and above the melting point of gutta‐percha. The evidence is that the rates of permeation and diffusion increase sharply at approximately 45°C., due to melting of the gutta‐percha. In the same way, although to a lesser degree, the solubility of the gas likewise increases at the melting point. The activation energies of permeation and diffusion with the heat of solution were computed from the temperature function of those quantities. It follows from the results that crystallization of the elastomer reduces the gas‐solubility, the diffusivity, and the permeability—and increases the activation energy of diffusion. The interpretation of this high activation energy of diffusion is that, because of the crystallization, the macromolecules of the membrane adhere so firmly that greater energy is required to admit the gas molecules.
Heats of polymerization of acrylic acid and derivatives
Authors: Evans Alwyn G. , Tyrrall E.
Published: April 2003

The heats of polymerization of acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate have been measured. Values for the heat of polymerization of unstrained polymer molecules have been calculated, and the low heat of polymerization of methyl methacrylate has been attributed to the presence of steric hindrance in the polymer molecule.
Course of acetylation and deacetylation reactions of cellulose fibers. I. Optical and swelling properties
Authors: Vermaas D. , Hermans P. H.
Published: April 2003

A description is given of the preparation, birefringence, and swelling capacity of a series of microscopically homogeneous, partially acetylated cellulose model filaments with an acetyl content varying from 0 to 2.3 acetyl groups per glucose residue, and obtained either by acetylation or by deacetylation. A higher degree of acetylation of these artificial fibers could not be attained without destruction of the fiber. The same holds true for native ramie fibers. The swelling was studied in water, acetone, and methanol. The degree of swelling of the filaments plotted against acetyl content yields entirely different curves for the acetylation and the deacetylation series. These curves can be readily explained by the hypothesis that the intercrystalline (so‐called amorphous) portion of the fiber substance is more accessible to the esterification and saponification reactions and is affected earlier than the crystalline portion. The birefringence of the acetylation series shows but a small—although apparently real—difference from that of the saponification series.