bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Combustion Mechanisms Using Global Uncertainty and Sensitivity Analyses: A Case Study for Low‐Temperature Dimethyl Ether Oxidation
Authors: Tomlin Alison S. , Agbro Edirin , Nevrlý Václav , Dlabka Jakub , Vašinek Michal
Published: September 2014

A global uncertainty analysis is performed for three current mechanisms describing the low‐temperature oxidation of dimethyl ether (Aramco Mech 1.3, Metcalfe et al., Int J Chem Kinet 2013, 45, 638–675; Zheng et al., Proc Combust Inst 2005, 30, 1101–1109; Liu et al., Combust Flame 2013, 160, 2654–2668) with application to simulations of species concentrations (CH2O, H2O2, CH3OCHO) corresponding to existing data from an atmospheric pressure flow reactor and high‐pressure ignition delays. When incorporating uncertainties in reaction rates within a global sampling approach, the distributions of predicted targets can span several orders of magnitude. The experimental profiles, however, fall within the predictive uncertainty limits. A variance‐based sensitivity analysis is then undertaken using high dimensional model representations. The main contributions to predictive uncertainties come from the CH3OCH2 + O2 system, with isomerization, propagation, chain‐branching, secondary OH formation, and peroxy–peroxy reactions all playing a role. The response surface describing the relationship between sampled reaction rates and predicted outputs is complex in all cases. Higher order interactions between parameters contribute significantly to output variance, and no single reaction channel dominates for any of the conditions studied. Sensitivity scatter plots illustrate that many different parameter combinations could lead to good agreement with specific sets of experimental data. The Aramco scheme is then updated based on data from a recent study by Eskola et al. (J Phys Chem A, in press), which presents quite different temperature and pressure dependencies for the rates of CH3OCH2O2 → CH2OCH2O2H and CH2OCH2O2H → OH+2CH2O compared with currently used values and includes well skipping channels. The updates from Eskola worsen the agreement with experiments when used in isolation. However, if the rate of the CH2OCH2O2H + O2 channel is subsequently reduced, very good agreement can be achieved. Owing to the complex nature of the response surface, the tuning of this channel remains speculative. Further detailed studies of the temperature and pressure dependence of the CH3OCH2O2 + O2, CH2OCH2O2H + O2 system are recommended to reduce uncertainties within current dimethyl ether mechanisms for low‐temperature conditions.
Insights into the Relationship of Catalytic Activity and Structure: A Comparison Study of Three Carbonic Anhydrase Mimics
Authors: MA RENHU , SCHUETTE GEORGE F. , BROADBELT LINDA J.
Published: September 2014

Density functional theory (DFT) calculations were used to study the mechanism of CO2 hydrolysis by Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam and evaluate the associated thermodynamic and kinetic parameters. Microkinetic models were then built based on the kinetics and thermodynamics derived from first principles. Both catalysts showed very similar behavior to Zn‐cyclen, which we have reported previously, but with multiple distinctions. The intrinsic reaction rate constants for Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam were calculated to be 2693 and 4623 M−1 s−1, respectively, which is in reasonable agreement with experimental values reported or estimated. The CO2 adsorption step was found to be a rate‐limiting step for all three catalysts. Zn‐cyclam has the lowest barrier for this step due to the highest pKa or nucleophilicity of the Zn‐OH− form, and, therefore, the highest intrinsic activity. However, the observed reaction rate constant also depends on the availability of the catalyst. The decrease in the observed reaction rate constant over 0–12 ms was ascribed to the decrease in the concentration of the catalytic form, Zn‐OH−, which was primarily converted to Zn‐HCO3−. The reaction rate constant of Zn‐cyclam dropped much faster than those of Zn‐cyclen and Zn‐(1,5,9‐triazacyclododecane) due to lower energy of the Zn‐HCO3− form. The conversion of CO2 at 1000 ms as a function of pH was calculated to compare the relative activity of these catalysts, and Zn‐cyclen was found to be the best catalyst.
A systematic review and meta‐analysis evaluating completeness and outcomes of robotic thyroidectomy
Authors: Lang Brian Hung‐Hin , Wong Carlos K. H. , Tsang Julian S. , Wong Kai P. , Wan Koon Y.
Published: September 2014

Objectives/Hypothesis

Despite immense interest, robotic‐assisted thyroidectomy (RT) remains controversial in differentiated thyroid carcinoma (DTC). This systematic review and meta‐analysis compared surgical completeness and/or oncological outcomes between RT and open thyroidectomy (OT) in low‐risk DTC.

Study Design

Systematic review.

Methods

A systematic review was performed to identify studies that compared surgical completeness and/or oncological outcomes between RT and OT in DTC. Any study that compared at least one parameter relating to surgical completeness and/or oncological outcome for DTC was considered. Number of central lymph nodes (CLNs) retrieved during central neck dissection (CND), preablation stimulated thyroglobulin (sTg) level, radioiodine uptake on post‐therapy scan, and locoregional recurrence (LRR) were examined. Meta‐analysis was performed using a fixed or random‐effects model depending on heterogeneity between studies.

Results

Ten studies were eligible. Of the 2,205 DTCs, 752 (34.1%) had RT, whereas 1,453 (65.9%) had OT. Relative to OT, RT had signif icantly fewer CLNs retrieved during CND (4.7 ± 3.2 vs. 5.5 ± 3.8, standardized mean difference [SMD] = −0.240, 95% confidence interval [CI]: −0.364 to −0.116, P < .001) and higher preablation sTg level (3.6 ± 6.7 ng/mL vs. 2.0 ± 5.0 ng/mL, SMD = 0.272, 95% CI: 0.022 to 0.522, P = .033). Interestingly, these differences were more evident in the robotic transaxillary approach (RTAA) than the robotic bilateral axillo‐breast approach. After a mean follow‐up of 17.7 months, no LRR was found in RT, whereas after 18.6 months, one LRR was found in OT.

Conclusions

Relative to OT, total thyroidectomy by RTAA was associated with fewer CLNs retrieved and less‐complete thyroid resection. However, using RTAA is unlikely to compromise the outcomes of low‐risk DTC because of its inherently good prognosis. Laryngoscope, 125:509–518, 2015
Intestinal ischemic preconditioning ameliorates hepatic ischemia/reperfusion injury in rats: Role of heme oxygenase 1 in the second window of protection
Authors: Kageyama Shoichi , Hata Koichiro , Tanaka Hirokazu , Hirao Hirofumi , Kubota Toyonari , Okamura Yusuke , Iwaisako Keiko , Takada Yasutsugu , Uemoto Shinji
Published: September 2014

Preconditioning by brief ischemia protects not only the concerned organ but also other distant organs against subsequent lethal damage; this is called remote ischemic preconditioning (RIPC). This study was designed to investigate the impact of intestinal RIPC on hepatic ischemia/reperfusion injury (IRI) with a special interest in heme oxygenase 1 (HO‐1) induction in the second window of protection (SWOP). Male Wistar rats were randomly assigned to 1 of 2 groups: an RIPC group or a sham group. Before hepatic IRI, either intestinal RIPC, consisting of 2 cycles of 4‐minute superior mesenteric artery clamping separated by 11 minutes of declamping (RIPC group), or a sham procedure (sham group) was performed. After 48 hours of recovery, the rats were exposed to 30 minutes of total hepatic IRI. Transaminase releases and proinflammatory cytokines were determined at several time points after reperfusion. Histopathological analysis and animal survival were also investigated. Intestinal RIPC significantly lowered transaminase release (alanine aminotransferase at 2 hours: 873.3 ± 176.4 IU/L for the RIPC group versus 3378.7 ± 871.1 IU/L for the sham group, P < .001) as well as proinflammatory cytokine production (tumor necrosis factor α at 2 hours: 930 ± 42 versus 387 ± 17 pg/μL, P < .001). The morphological integrity of the liver and the ileum was maintained significantly better with intestinal RIPC; this reached statistical significance not only in Suzuki's liver injury score (3.5 ± 0.2 versus 0.7 ± 0.5, P = .007) but also in Park's score for intestinal damage (4.0 ± 0.4 versus 2.0 ± 0.2, P = .007). Animal survival was also markedly improved (83.1% versus 15.4%, P < .001). As a mechanism underlying this protection, HO‐1 was substantially induced in liver tissue, especially in hepatocytes, with remarkable up‐regulation of bradykinin in the portal blood, whereas HO‐1 protein induction in enterocytes was not significant. In conclusion, intestinal RIPC remarkably attenuates hepatic IRI in the SWOP, presumably by HO‐1 induction in hepatocytes. Liver Transpl 21:112‐122, 2015. © 2014 AASLD.
Asiatic acid induces endoplasmic reticulum stress and apoptotic death in glioblastoma multiforme cells both in vitro and in vivo
Authors: Kavitha Chandagirikoppal V. , Jain Anil K. , Agarwal Chapla , Pierce Angela , Keating Amy , Huber Kendra M. , Serkova Natalie J. , Wempe Michael F. , Agarwal Rajesh , Deep Gagan
Published: September 2014

Glioblastoma multiforme (GBM) is an untreatable malignancy. Existing therapeutic options are insufficient, and adversely affect functional and non‐cancerous cells in the brain impairing different functions of the body. Therefore, there is an urgent need for additional preventive and therapeutic non‐toxic drugs against GBM. Asiatic acid (AsA; 2,3,23‐trihydroxy‐12‐ursen‐28‐oic acid, C30H48O5) is a natural small molecule widely used to treat various neurological disorders, and the present research investigates AsA's efficacy against GBM both in vitro and in vivo. Results showed that AsA treatment (10–100 µM) decreased the human GBM cell (LN18, U87MG, and U118MG) viability, with better efficacy than temozolomide at equimolar doses. Orally administered AsA (30 mg/kg/d) strongly decreased tumor volume in mice when administered immediately after ectopic U87MG xenograft implantation (54% decrease, P ≤ 0.05) or in mice with established xenografts (48% decrease, P ≤ 0.05) without any apparent toxicity. Importantly, AsA feeding (30 mg/kg/twice a day) also decreased the orthotopic U87MG xenografts growth in nude mice as measured by magnetic resonance imaging. Using LC/MS‐MS methods, AsA was detected in mice plasma and brain tissue, confirming that AsA crosses blood‐brain barrier. Mechanistic studies showed that AsA induces apoptotic death by modulating the protein expression of several apoptosis regulators (caspases, Bcl2 family members, and survivin) in GBM cells. Furthermore, AsA induced ER stress (increased GRP78 and Calpain, and decreased Calnexin and IRE1α expression), enhanced free intra‐cellular calcium, and damaged cellular organization in GBM cells. These experimental results demonstrate that AsA is effective against GBM, and advocate further pre‐clinical and clinical evaluations of AsA against GBM. © 2014 Wiley Periodicals, Inc.
Comparison of brain gray and white matter macromolecule resonances at 3 and 7 Tesla
Authors: Snoussi Karim , Gillen Joseph S. , Horska Alena , Puts Nicolaas A. J. , Pradhan Subechhya , Edden Richard A. E. , Barker Peter B.
Published: September 2014

Purpose

In proton MR spectra of the human brain, relatively broad macromolecule (MM) resonances underlie the narrower signals from metabolites. The purpose of this study was to quantify the MM profile in healthy human brain at 3T and 7T, both in gray matter (anterior cingulate cortex [ACC]) and white matter (centrum semiovale [CSO]).

Methods

A water‐suppressed, inversion‐recovery pulse sequence was used to null metabolite signals and acquire MM spectra in 20 healthy volunteers using very similar methodology at both field strengths (n = 5 per region and field). The MM spectra were fitted with multiple Gaussian functions and quantified relative to the unsuppressed water signal from the same volume.

Results

MM proton concentration values were in the range of 5–20 mmol/kg. No significant differences were found between the MM proton concentration measurements by region (P ≈ 0.8) nor by field strength (P ≈ 0.5). Linewidths of the well‐resolved M1 peak were slightly more than double at 7T (43.0 ± 4.7 Hz in ACC, 45.6 ± 4.1 Hz in CSO) compared with 3T (19.8 ± 3.5 Hz in ACC, 20.0 ± 4.3 Hz in CSO).

Conclusion

The absence of differences in MM concentrations between white and gray matter implies that a single MM “baseline” may be adequate for spectral fitting of multiple brain regions when determining metabolite concentrations. Visibility of MM signals is similar at 3T and 7T. Magn Reson Med 74:607–613, 2015. © 2014 Wiley Periodicals, Inc.
Etoposide and carbo‐or cisplatin combination therapy in refractory or relapsed Ewing sarcoma: A large retrospective study
Authors: van Maldegem Annemiek M. , Benson Charlotte , Rutkowski Piotr , Blay Jean‐Yves , van den Berg Henk , Placzke Joanna , Rasper Meybrit , Judson Ian , Juergens Heribert , Dirksen Uta , Gelderblom Hans
Published: September 2014

Background

Patients with Ewing sarcoma (EWS) who develop refractory or relapsed disease have limited treatment options. In some sarcoma centres in Europe the combination of etoposide with carbo‐ or cisplatin is being used for these patients, however, there are no published data available yet. Here we investigated the outcome of the combination treatment for patients with advanced Ewing sarcoma in progression after standard treatment.

Procedure

All patients diagnosed with EWS between 1980 and 2012 in one of six major sarcoma centres in Europe and treated with either carboplatin and etoposide or cisplatin and etoposide were included and data were retrospectively collected for analysis.

Results

A total of 107 patients enrolled in this study of which 61 received the combination of etoposide and carboplatin and 46 received etoposide and cisplatin. The median overall survival (OS) was 23 months for both patient groups and the 5‐year OS was 24.5% for the patients who received carboplatin and etoposide and 20% for those who received cisplatin and etoposide. The progression free survival was better in patients treated with the combination of carboplatin and etoposide (14.5 vs. 6.3 months P = 0.023).

Conclusion

This is a retrospective study on the combination treatment of etoposide and carbo‐ or cisplatin in refractory Ewing sarcoma. The results justify exploring the combination in a prospective study with relapsed patients. Pediatr Blood Cancer 2015;62:40–44. © 2014 Wiley Periodicals, Inc.
SUMO proteomics to decipher the SUMO‐modified proteome regulated by various diseases
Authors: Yang Wei , Paschen Wulf
Published: September 2014

Small ubiquitin‐like modifier (SUMO1–3) conjugation is a posttranslational protein modification whereby SUMOs are conjugated to lysine residues of target proteins. SUMO conjugation can alter the activity, stability, and function of target proteins, and thereby modulate almost all major cellular pathways. Many diseases are associated with SUMO conjugation, including heart failure, arthritis, cancer, degenerative diseases, and brain ischemia/stroke. It is, therefore, of major interest to characterize the SUMO‐modified proteome regulated by these disorders. SUMO proteomics analysis is hampered by low levels of SUMOylated proteins. Several strategies have, therefore, been developed to enrich SUMOylated proteins from cell/tissue extracts. These include proteomics analysis on cells expressing epitope‐tagged SUMO isoforms, use of monoclonal SUMO antibodies for immunoprecipitation and epitope‐specific peptides for elution, and affinity purification with peptides containing SUMO interaction motifs to specifically enrich polySUMOylated proteins. Recently, two mouse models were generated and characterized that express tagged SUMO isoforms, and allow purification of SUMOylated proteins from complex organ extracts. Ultimately, these new analytical tools will help to decipher the SUMO‐modified proteome regulated by various human diseases, and thereby, identify new targets for preventive and therapeutic purposes.
Nuclear magnetic resonance analysis of some deuterated polypropenes
Authors: Lombardi E. , Segre A. , Zambelli A. , Marinangeli A. , Natta G.
Published: September 2014

High resolution 60 and 100 Mc. NMR spectra have been obtained for a series of deuterated polypropenes with compounds of the highest sterical purity used. The fundamental parameters of the spectra (chemical shifts and coupling constants) have been accurately determined and compared with previous results available in the literature. The results may be applied to quantitative estimates of the stereoregularity of polymers not deuterated by the NMR method.
Étude de la Compatibilité des Copolymères avec les Homopolymères Correspondants. Système: Polystyrène—Polyméthacrylate de Méthyle
Authors: Banderet Albert , Tournut Claude , Riess GÉRard
Published: September 2014

L'incompatibilité entre deux homopolymères étant de règle générale, il est intéressant d'examiner si on peut rendre compatible un mélange de deux homopolymères incompatibles en y adjoignant un des copolymères correspondant, copolymère à séquences ou copolymère statistique. Nous nous bornons ici à l'étude du système styrène–méthacrylate de méthyle, polymères atactiques, essentiellement parce qu'on n'observe pas de phénomène de cristallisadans ces systèmes. L'étude du système à l'état solide et notamment l'observation des films obtenus par évaporation des solutions, permet de situer assez bien les domaines de compatibilité. Les paramètres essentiels de la compatibilité des mélanges copolymères–homopolymères sont leur composition et, par ailleurs, les masses moléculaires et la structure du copolymère. Les diagrammes ternaires, pour les mélanges de deux homopolymères et d'un copolymère, montrent nettement que les copolymères séquencés sont les seuls à assurer une certaine compatibilité, surtout si ce copolymère a une composition avoisinant 50–50 et si les homopolymères ont des masses moléculaires inféireures à celles des séquences. Les autres copolymères greffés ou statistiques sont pratiquement sans effet.
Der Ringöffnungsmechanismus des Diäthylenglykolformals bei der kationischen Polymerisation
Authors: Weichert D.
Published: September 2014

Während der Untersuchung polymerisierbarer zyklischer Formale beschäftigten wir uns mit dem Problem der Ringöffnung des Diäthylenglykolformals. Aus der Struktur dieses Formals folgt, dass zwei Sauerstoffatome der Formalgruppe und ein Äthersauerstoff Oxoniumkomplexe bilden können. Natürlich war es theoretisch möglich, für den Formalsauerstoff eine höhere Reaktivität vorauszusagen, da das benachbarte Sauerstoffatom als Elektroacceptor das Karbeniumkation begünstigt. Obgleich der Formalrest besonders begünstigt für die Ringöffnung ist, sollen andere Mechanismen, z. B. zwischen dem benachbarten C‐Atom des Diäthylenglykolteils und des Formalsauerstoffs, diskutiert werden. Unter Berücksichtigung der Strukturen, die sich von verschiedenen Mechanismen ableiten, und bei Ausdehnung dieser theoretischen Modelle auf kombinierte würde schliesslich eine Abweichung von der klassischen Formalstruktur ergeben. Da in einigen Fällen neue Ätherbindungen geknüpft würden, müssten sich neue Verbindungen neben den erwarteten Diäthylenglykol und CH2O, wie z. B. Tri‐, Tetra‐ und Monoäthylenglykol nach der Azidolyse bilden. Es wurde versucht, den Äthylenglykolgehalt mit Hilfe der hochempfindlichen und spezifischen Perjodatmethode zu bestimmen. Innerhalb der Genauigkeit dieser Methode konnte kein Äthylenglykol in den Hydrolysaten entdeckt werden. Die Gaschromatographie ergab nur Diäthylenglykol im hydrolysierten Polyformal. Das gleiche Ergebnis ergab die fraktionierte Destillation. Unter Berücksichtigung dieser Ergebnisse konnten drei Ringöffnungstypen verworfen werden, so dass nur noch die Ringöffnung zwischen dem Sauerstoff und der Methylengruppe des Formalrestes postuliert wird.
Helix—Coil transition in some helical macromolecules
Authors: Gupta V. D. , Gupta A. K.
Published: September 2014

A statistical thermodynamic approach based on the application of the Ising model for ferromagnetism is outlined to explain the phase transition in isolated single‐stranded helical macromolecules. The transition is characterized by the degree of helicity and the lengths of uninterrupted helical and random‐coil regions. The theoretical predictions for the temperature dependence of helicity in case of poly‐l‐lysine and poly(l‐glutamic acid) are compared with the experimental results of Applequist and Doty and Doty, Yang, and others. The application of the theory to the crystalline–amorphous transition in polyethylene and polypropylene is also suggested and some preliminary results are reported.
Casting of transparent polyacrylonitrile
Authors: Oplatka Avraham , Konigsbuch Mordechai , Shavit Nehemia
Published: September 2014

The bulk polymerization of acrylonitrile (AN) has been reported to give a white precipitate which then solidifies to a hard opaque aggregation of polymer particles. Contrary to the bulk polymerization of, say, methyl methacrylate, that of AN cannot therefore be considered as a cast polymerization process. We have found that by using catalytic amounts of mercury nitrates as initiators, the white slurry obtained during the early stages of the polymerization was transformed spontaneously, at higher degrees of conversion, into a transparent material which acquired the shape of the mold. The glass, contrary to the transparent gels obtained by Salomon,7 who used high concentrations of AgNO3 in AN, does not lose its transparency in water and is thus a real transparent plastic like poly(methyl methacrylate). The work was extended to examine the polymerization of AN by other mercury salts as well as by the salts of a number of other cations. Various properties of the new plastic obtained with Hg(NO3)2 were determined and compared with those of ordinary powdery PAN. Essentially, at the molecular level, the polymers do not seem to differ, and the difference in light transmission is ascribed to a difference in physical states. A qualitative mechanism for glass formation is suggested.
Chain conformation and crystal structure of the α‐polymorphic form of poly(dimethyl ketene)
Authors: Bassi I. W. , Ganis P. , Temussi P. A.
Published: September 2014

The chain structure of the two polymorphic forms of poly(dimethyl ketene) has been determined with the aid of internal energy calculations, theoretical characterization of polymer chain geometry, and finally by a complete x‐ray analysis. In the α form, a chain conformation containing a glide‐plane has been found, which along with the value of the identity period of the structural unit (4.4 A.) requires the structural unit to be composed of two monomeric units. An AB3AC3 conformation has been assigned and subsequently confirmed by the determination of the crystalline structure.
Zur Lichtstreuung an Lösungen verzweigter Makromoleküle. III. Verschiedene Verzweigungsmodelle
Authors: Dautzenberg H. , Ruscher Ch.
Published: September 2014

Während bisher nur Näherungen für die Lichtstreufunktionen von verschieden verzweigten Kettenmolekülen beschrieben worden sind, werden von uns nunmehr die exakten Streufunktionen berechnet, und zwar für das Kamm‐Modell, das Kaskaden‐Modell mit 1, 2 und 3 Verzweigungsstufen und das Stern‐Modell.
Investigation of the kinetics and mechanism of radiochemical and photochemical grafting of acrylonitrile from the gaseous phase to polyamide fibers
Authors: Kachan A. A. , Chervyatsova L. L. , Kornyev K. A. , Mertvichenko E. F. , Gnyp N. P.
Published: September 2014

Grafting from the vapor phase of acrylonitrile, vinyl acetate, vinylpyridine, and isoprene to polyamide fibers was effected by radiation and photochemical initiation. The absence of a homopolymer in vapor‐phase grafted polymerization made it possible to take its kinetics continuously during the reaction in adsorption vessels with the aid of MacBen scales. Dependences of the reaction rate on the radiation dose, monomer vapor pressure, duration of experiment, and temperature are obtained. The basic kinetic peculiarities of the process are studied on a model reaction of grafted polymerization of acrylonitrile on capron fiber. Grafting is shown to occur chiefly according to an “impact” mechanism. The observed negative temperature coefficient of the reaction is due chiefly to the decay of free radicals. Values are obtained on the increment rate and chain scission constants at 22, 40, and 60°C., and the corresponding activation energy values. The quantum yield of free radical formation on capron is calculated for a wavelength of 2537 A. (G = 1.7 × 10−5). The results of the calculation of G are compared with those obtained by measuring the ESR spectra.
On radiochemical crosslinking of polyolefins in the presence of sulfur monochloride
Authors: Kachan A. A. , Chervyatsova L. L. , Kaurkova G. K.
Published: September 2014

It was found that in the presence of sulfur monochloride the gamma radiation dose may be considerably reduced during the radiochemical crosslinking of polyolefins. Thus, in the case of polyethylene practically complete crosslinking is attained with a dose of 0.1 Mrad, i.e., by three orders lower than with ordinarily used radiation doses. Sulfur monochloride was introduced from the vapor phase, which made it possible to apply S2Cl2 uniformly on the polymer, to control strictly the quantity of introduced substance, and to reduce its consumption sharply. Some peculiarities of the mechanism of the action of sulfur monochloride in the process of radiochemical crosslinking of polyethylene are clarified. It is shown that in polyethylene crosslinking occurs chiefly on bonds of the monosulfide type. The value of the radiochemical yield of cross‐bond formation was 1.25 × 103.
Détermination de la Structure des Poly‐2,3‐Diméthyl‐1,3 Butadiènes par Résonance Magnétique Nucléaire et Spectrographie Infrarouge
Authors: Assioma François , Marchal Jean , Schue François , Friedmann Gilbert , Maillard Alfred
Published: September 2014

With the shifts observed on the frequencies corresponding to the symetric absorption band of the CH3 groups, it has been possible to make a complete analysis of the microstructure of the poly‐2,3 dimethyl‐1,3 butadienes by IR spectroscopy. We have determined the δs CH3 frequencies for the three possible modes of addition and the corresponding absorbtivities, by mean of polymers all 1,4 cis, all 1,4 trans, and polymers with approximately 50% of 1.2 addition. The quantitative determination of this addition has been made at 888 cm.−1, corresponding to the out‐of‐plane deformation of the two hydrogen on the double band CC in the isopropenyl group. The results are in good agreement with those of NMR analysis.
Cyclo‐ and cyclized diene polymers. VII. cyclopolymerization of 2,3‐dimethylbutadiene‐1,3 and infrared spectra of poly(2,3‐dimethylbutadiene‐1,3)
Authors: Gaylord Norman G. , Kössler Ivo
Published: September 2014

2,3‐Dimethylbutadiene‐1,3 was polymerized with cationic and Ziegler type catalysts and by radical polymerization. Polymers with linear and cyclic structure and copolymers with the dimer of 2,3‐dimethylbutadiene‐1,3 were obtained. The structure of the polymers was determined by infrared spectra.
Conformation and flexibility of some polypeptides in solution
Authors: Tsvetkov V. N. , Shtennikova I. N. , Skazka V. S. , Rjumtsev E. I.
Published: September 2014

The flow and electric birefringence of a number of poly‐γ‐benzyl‐l‐glutamate (PBLG) fractions in dichloroethane and m‐cresol have been studied. Molecular weights (0.4–3.4 × 105) of the fractions are determined from measurements of diffusion and sedimentation of solutions. The hydrodynamic, optical, and electrical data obtained are used for quantitative evaluation of molecular conformation and flexibility. From the experimental dependence of molecular optical anisotropy on molecular weight, an apparent persistence length a = 1200 A. is calculated for the PBLG chain. This value is obtained by using both the intrinsic anisotropy of molecules and their microform anisotropy. A similar value, a = 1100 A., is also obtained from the dependence of diffusion and sedimentation coefficients on molecular weight. The value a = 700 A. determined from the dependence of dipole moment upon molecular weight appears to be considerably lower. This means that orientation processes of polar PBLG molecules in mechanical and electrical fields should not be considered identical and that a marked difference exists in the correlation of molecular chain segments with the phenomena of flow and electrical birefringence.
Stereospecific polymerization of butadiene with cyclopentadienyl and carbonyl VIII group metal complexes
Authors: Babitskii B. D. , Kormer V. A. , Lapuk I. M. , Skoblikova V. I.
Published: September 2014

Butadiene polymerization with carbonyl and cyclopentadienyl nickel complexes combined with Lewis acids has been investigated. The microstructure of polybutadiene obtained is shown to be influenced by the nature of metal in π‐complex and independent of Lewis acid metal. In all cases polymers produced are mainly of 1,4 structure. Catalysts prepared by the reaction of nickel carbonyl with Lewis acids in aromatic hydrocarbons are arene nickel complexes. The activity of these catalysts is found to be dependent on the lability of arene–metal bond. It is suggested that there exists a genetic relation between catalyst systems studied and π‐allylic nickel complexes, which is supported by the same influence of the nature of halogen on polybutadiene microstructure.
Polycondensats Linéaires Obtenus à Partir de Monomères Triaziniques
Authors: Audebert Roland , Néel Jean
Published: September 2014

Dichlorotriazinic monomers prepared by the reaction of cyanuric chloride with an amine or a Grignard reagent are polycondensed with bisphenols as well as with diamines. Linear polymers thus obtained an analyzed and identified and their physical constants have been determined. Particularly, their behaviour towards heat, solubility, molecular weight, cristallinity and IR absorption spectra have been examined.
The aging of some pigmented polymeric films
Authors: Skledar Š.
Published: September 2014

Pigmented films based on different polymers and their blends have been prepared on pine‐wood and low‐carbon steel substrates, and exposed in laboratory and out‐of‐doors. In the high humidity cabinet, films based on pentaerythritol alkyd modified with 65% linseed oil and applied to a pine‐wood surface, deteriorated by blistering, except those pigmented with titanium dioxide. A blend of the same medium with stabilized chlorinated rubber showed good resistance to degradation in high humidity conditions as well as in marine and industrial environments. In the latter system, especially the combined pigmentations zinc oxide/rutile behaved very well on aging. However, in linseed oil varnish, the combined pigmentation zinc oxide/rutile/basic lead carbonate protected the exposed films very well. The rutile modification of titanium dioxide protects a polymeric film by absorbing ultraviolet light which would otherwise damage it. Also, zinc oxide indicates complete absorption of the shorter wavelengths, and basic lead carbonate transmits much more ultraviolet light. Nevertheless, lead and zinc soap formation with free acids might affect various film properties in the above pigment combination. The highest retention of whiteness was exhibited by the film samples exposed to a marine environment, and the lowest by those exposed to an industrial atmosphere.
The effect of crosslink structure on the tensile strength and oxygen absorption characteristics of natural rubber vulcanizates
Authors: Lal Joginder
Published: September 2014

The chemical nature of crosslinks in natural rubber–sulfur‐diphenylguanidine vulcanizates was modified by reaction with triphenylphosphine under nitrogen to determine the effect of this change on tensile strength and oxygen absorption characteristics of the vulcanizates. The vulcanizates were characterized by organically combined sulfur and polysulfidic sulfur. Polysulfidic crosslinks, i.e., crosslinks containing three or more sulfur atoms in the crosslink, were found not to be essential for the attainment of high tensile strength in these vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples.

Vulcanizates which had been reacted with triphenylphosphine for 16 days at 80°C., had lost 95–99.6% of their polysulfidic sulfur. These triphenylphosphine‐reacted vulcanizates exhibited significantly lower rates of oxygen absorption at 100°C. as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.
The models of the denaturation of globular proteins. III. The intramolecular β‐structure coil transitions in poly‐S‐carbobenzoxymethyl‐l‐cysteine
Authors: Anufrieva E. V. , Birshtein T. M. , Bolotina I. A. , Burshtein L. L. , Eskin V. E. , Frolov V. I. , Illarionova N. G. , Kalikhevich V. I. , Korotkina O. Z. , Mitin Yu. V. , Ptitsyn O. B. , Purkinas A. V. , Volchek B. Z.
Published: September 2014

Conformational transitions in synthetic poly‐S‐carbobenzoxymethyl‐l‐cysteine (PCBMC) have been investigated in order to model the processes of the denaturation of globular proteins. The solutions of some samples of PCBMC in the mixtures of nonpolar solvents (dichloroethylene, chloroform) with highly polar solvents (dichloroacetic or trifluoroacetic acids) have been studied by viscosimetric, polarimetric, spectroscopic, and dielectric methods, as well as by light scattering and electronic microscopy. Intrinsic viscosity and levorotation increase sharply when solvent breaking hydrogen bonds are added in the narrow range of the solvent composition, the molecular weight (measured by light scattering) remaining constant. It means that intramolecular cooperative conformational transition occurs in the PCBMC molecules. The dispersion of optical activity shows the absence of the helical structures in PCBMC molecules for any solvent composition. Infrared spectra show that the PCBMC molecules possess β‐structure in inert solvents and in films; and viscometric and polarimetric data suggest that this structure is an intramolecular one and corresponds to the compact shape of the PCBMC molecules in solution. The compact structure of PCBMC molecules in nonpolar solvents is also confirmed by dielectric data. The experimental results permit us to draw the conclusion that cooperative conformational transition involving intramolecular β‐structure statistical coil occurs in PCBMC when solvent breaking hydrogen bonds are added. The position and the degree of sharpness of the transition do not depend on the molecular weight of the sample in the interval investigated (from 15,000 to 91,000). The “plate” model of the intramolecular β‐structure has been proposed which does not contradict the results of the electron microscopic study. An assumption is made that owing to the two dimensional character of the intramolecular cross‐β‐structure its melting occurs in accordance with the “all‐or‐none” principle.
Thermal polymerization of trimeric phosphonitrilic chloride
Authors: Colclough R. O. , Gee Geoffrey
Published: September 2014

Trimeric phosphonitrilic chloride, when purified by a sequence of operations involving recrystallization, refluxing at 130°C. over barium oxide in an atmosphere of dry nitrogen, passage of the vapor at 130°C. over phosphorus pentoxide, followed by repeated sublimation with degassing in a high‐vacuum, all‐glass apparatus, polymerizes only very slowly at 300°C., and polymerization is sharply accelerated on admission of dry oxygen. Crude trimer, which was purified by only a single vacuum sublimation, polymerized relatively rapidly at 270°C. The conversion–time curve for the highly purified trimer shows a continuously accelerating rate of polymerization up to high conversion at 320 and 340°C.
Étude des Propriétés Catalytiques des Composés d'Insertion des Metaux Alcalins dans le Graphite
Authors: Golé J. , Stein C.
Published: September 2014

The lamellar compounds of alkali metals and graphite were tested as polymerization initiators of vinyl monomers. Cinetic studies of the styrene—C32K system showed that the rate of polymerization was directly proportional to the initiator concentration and to the three‐halves power of the monomer concentration. The activation energy of styrene was found to be 19 kcal./mole. These initiators lead to very high molecular weights (\documentclass{article}\pagestyle{empty}\begin{document}$ \[\bar M_w > 10^7 \] $\end{document} > 107 for polystyrene). A mechanism of polymerization based on our experiments is proposed.
The relationship of performance characteristics to basic parameters of polymers. I. A collaborative study of polystyrene using torsion pendulum and impact methods
Authors: Jones T. T.
Published: September 2014

In July, 1963, a working party of I.U.P.A.C. was set up to consider collaborative investigations in the general area indicated by the main title of this paper, and joint studies were started with three polymers: polystyrene, polyvinyl chloride, and polyethylene. This paper gives an account of the work done to date with polystyrene. The paper shows the detailed torsion pendulum results of six laboratories with the use of the same toughened polystyrene. The significance of frequency of vibration in raising the temperature of maximum damping of the rubbery component is clearly brought out and the degree of agreement shown between laboratories is good. A smaller number of collaborators made impact strength and torsion pendulum studies over a range of temperatures on polystyrene and another toughened polystyrene. The dependence of the brittle–tough transition temperature on estimated rate of elongation of the breaking filament is correlated with the dependence of the temperature of maximum damping of the rubbery component on frequency.
Mechanism of anionic polymerization of acrylates and methacrylates
Authors: Báča J. , Lochmann L. , Jůzl K. , Čoupek J. , Lím D.
Published: September 2014

The mechanism of anionic polymerization of acrylates and methacrylates was studied by differential thermometry. The course of the temperature curves after the addition of the initiator to the monomer was analyzed. As initiator, organolithium and sodium compounds as well as lithium, sodium, and potassium tert. alkoxides were used. It was found that in case of methacrylates the lifetime of growing chains is according to the type of the initiator and monomer from seconds to about 1 min. In the case of lithium alkoxide, formation of active centers is a relatively slow process, different from potassium alkoxide, where the whole process resembles polymerization by organometallic compounds. Sodium alkoxide initiator evidently causes a very complicated process. After the region of acceleration is reached, polymerization resembles potassium alkoxide initiation. In the case of lithium compounds the high isotactic portion depends on the alkoxide present, whereas with sodium compounds, atactic polymer is normally obtained. Potassium alkoxide leads to slightly increased syndiotactic portion.
Graft copolymerization via polymeric initiators
Authors: Reynolds G. E. J.
Published: September 2014

Poly(styrene‐alt‐maleic anhydride) was prepared by polymerization in benzene, a nonsolvent for the product, and from it partial peresters were prepared in acetone solution, with t‐butyl hydroperoxide and pyridine used as catalyst. The partial peresters were used to initiate methyl methacrylate polymerization by a thermal mechanism in homogeneous solution in acetone, and both homopolymer and graft copolymer were formed. Acrylonitrile was polymerized in aqueous solution by a redox mechanism, and here graft copolymer was produced, but there was no evidence of homopolymer. Parallel polymerizations with poly(styrene‐alt‐maleic anhydride) showed that this had no initiating activity in either system. With methyl methacrylate polymerization thermally initiated with t‐butyl hydroperoxide in the presence of poly(styrene‐alt‐maleic anhydride), grafting by transfer was shown to be substantially less than grafting produced via perester polymers.
Étude par Diffusion de la Lumière de Films de Polystyrène Isotactique
Authors: Picot C. , Weill G. , Benoit H.
Published: September 2014

Light scattering by isotactic polystyrene films has been studied by a photographic technique. By changing the refractive index of the surrounding of the spherulites, it has been shown that only the anisotropic disk model explains the light scattering photographs. The modification of the light‐scattering patterns during an isothermal crystallization has been interpreted as an effect of the variation of the surrounding of the spherulites. The spherulites dimensions can be measured by this technique and experimental measurements of the radial growth of the spherulites are in good agreement with optic microscopic measurements.
Préparation de Polystyrènes à Ramification Contrôlée
Authors: Rempp Paul , Decker‐Freyss Danielle
Published: September 2014

Preparation of branched “comblike” polystyrene has been performed by two different methods derived from the anionic grafting techniques. Grafting by carbanionic initiation can be utilized: as its basis we have used statistical copolymers of styrene and p‐bromostyrene. Partial metallation of the p‐bromostyrene units is performed by naphthalene—lithium and the metallated sites are used as initiators for the polymerization of styrene. Thus, branched polystyrene samples were obtained. Grafting by carbanionic deactivation has also been applied. The “backbone” chain is a statistical copolymer of styrene and methylmethacrylate. The ester functions are used as electrophilic deactivators for “living” polystyrene chains. Easily characterizable samples of low polydispersity have been obtained, fractionated, studied by light scattering, and characterized as “comb” polymers. The advantages and disadvantages of both methods are discussed.
Polycycloaddition of terephthalonitrile oxide
Authors: Overberger C. G. , Fujimoto Sumio
Published: September 2014

Terephthalonitrile oxide (TNO) of various crystalline states was prepared and its structure was studied by infrared spectroscopy, x‐ray diffraction, and hydrolysis. Biscycloadditions of unsaturated compounds such as ethynylbenzene, styrene, benzonitrile, and cyclopentadiene were found to yield 1,4‐bis(5‐phenyl‐3‐isoxazolyl)‐benzene, 1,4‐bis‐(5‐phenyl‐3‐isoxazolinyl)‐benzene, 1,4‐bis‐(5‐phenyl‐1,2,4‐oxadiazolyl)‐benzene, and 1,4‐bis‐(4,5‐cyclopent‐3′‐ene‐3‐isoxazolinyl)‐benzene, respectively. Solution polymerization of TNO gave a polyfuroxan, which had an alternating structure of p‐phenylene and furoxan rings. Polymerization of TNO in the solid state also gave a polymer, whose structure was postulated as a polyoxazoxime. Copolymerizations of TNO with bifunctional unsaturated compounds such as 1,4‐diethynylbenzene, terephthalonitrile, cyclopentadiene, quinone, and allene yielded 1:1 alternating copolymers containing p‐phenylene units and corresponding ring structures.
Beziehungen zwischen den dynamischen Eigenschaften und der Schlagzähigkeit der Mischungen des Polyvinylchlorids mit Kautschuk
Authors: Zelinger Jiří
Published: September 2014

Measurements of dynamic properties of a series of polyvinylchloride‐rubber blends at temperatures of −60 to +100°C and frequencies of 0.3–3.0 Hz have been carried out by means of the free vibration method. The dynamic data have been compared to the results of impact resistance Charpy‐experiments. The linear correlation obtained between the dynamic shear modulus at −10°C (G′−10) and the impact resistance at 20°C indicated that the value G′−10 has to be decreased compared to that of unmodified PVC to increase the resistance of compatible as well as incompatible PVC‐rubber blends. The impact resistance increases with higher decrease of G′−10. The correlation given and the breaking characteristics of the samples investigated show that, ductile fracture, relieving the deformational stress mainly by developing cracks, occurs in blends with G′−10 in the range of 12.0–7.5 × 108 N/m2. This is valid for compatible as well as incompatible PVC rubber blends.
Über einige elektrische Eigenschaften von Metall—Tetracyanoäthyleniden und ihren Polymeren
Authors: Storbeck I.
Published: September 2014

A copper tetracyanoethylene polymer has been prepared and its thermal stability investigated. Direct current resistivity, thermo e.m.f., and thermal conductivity of the initial product and of the annealing products have been determined as a function of temperature. The relative dielectric constant has been measured in the frequency range of 50 cps to 500 kc./sec. The electric measurements and infrared spectra allowed to conclude that destruction of the polymers by copper degradation occurs at 250–300°C.
Über Bildung und Zerfall von Peroxiden in strahlenoxydiertem Polyvinylchlorid (PVC)
Authors: Zeppenfeld G. , Bartl A.
Published: September 2014

We succeeded in determining quantitatively hydroperoxides and peroxiradicals in radiation‐oxidized polyvinyl chloride (PVC) by combining the chemical method with electron paramagnetic resonance. PVC oxidized by radiation contains two different kinds of peroxiradicals and one of hydroperoxide. 60% of peroxiradicals decay at 20°C in atmospheric oxygen at a half time T½ ∼ 3 hr. 40% of peroxiradicals are relatively stable at room temperature. They decay at 56°C. in vacuum with T½ ∼ 40 hr. The hydroperoxide R″COOH decays at 50°C. in vacuum with T½ = 650 hr. The activation energy of decay is E = 35 kcal./mole in a temperature range of 50 to 75°C.
Contribution à l'Étude de la Polymérisation Radiochimique de l'Isopréne en Phase Solide
Authors: Hinschberger André , Marchal Jean , Vacherot Monique , Dworkin Ary , Roncin Jean
Published: September 2014

The study by calorimetry of the γ irradiation induced polymerization of isoprene in the solid state showed that the reaction took place through irradiation. No post‐effect was observed while heating the polymer from the irradiation temperature to the melting point. Gas chromatography analysis showed that, with respect to the polymer, the proportion of minor products resulting from irradiation was small. After UV irradiation of solid isoprene we found the same radical, vinyl 2‐allyl, as after γ irradiation.
Détermination de la Polydispersité en Masse Moléculaire et en Composition Chimique d'un Copolymère Greffé Poly(isobutylene) Poly(Styrène) Préparé Par Voie Radiochimique
Authors: Danon Jeanne , Jozefowicz Jacqueline
Published: September 2014

A graft copolymer of polyisobutylene–polystyrene prepared radiochemically and possessing both a molecular weight polydispersity and chemical heterogeneity has been fractionated by elution on a column. The system solvent–precipitant has been chosen in order to produce a fractionation essentially on the basis of the molecular weight. Some fractions have been examined by light diffusion in order to determine their polydispersities of molecular weight and of chemical composition. This study permits the conclusion that the fractionation was indeed obtained on the basis of molecular weight differences.
New monomers involving nitrogen and sulfur and their polymers
Authors: Sidelkovskaya F. P. , Avetisyan A. A. , Zelenskaya M. G.
Published: September 2014

Vinyl and allyl derivatives of cyclic thioamides containing an unsaturated radical at nitrogen or sulfur have been synthesized and their homopolymers and copolymers prepared. The synthesized polymers were converted to other polymers by suitable reactions.