scholarly journals A New Formation Process of Poly(phenylsilsesquioxane) in the Hydrolytic Polycondensation of Trichlorophenylsilane. Isolation of Low Molecular Weight Hydrolysates to Form High Molecular Weight Polymers at Mild Reaction Conditions

1997 ◽  
Vol 29 (8) ◽  
pp. 678-684 ◽  
Author(s):  
Eung-Chan Lee ◽  
Yoshiharu Kimura
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Formation Process ◽  
Low Molecular Weight ◽  
Reaction Conditions ◽  
Hydrolytic Polycondensation ◽  
High Molecular Weight Polymers ◽  
New Formation

Toxicological Considerations in the Selection of Flexible Packaging Materials for Foodstuffs

1977 ◽  
Vol 40 (1) ◽  
pp. 65-68 ◽  
Author(s):  
FRED B. SHAW
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Polymeric Films ◽  
Low Molecular Weight ◽  
High Molecular Weight Polymers ◽  
Flexible Packaging ◽  
Aseptic Packaging ◽  
Commercial Polymers ◽  
Metallic Foils ◽  
Molecular Weight Fractions

High molecular weight polymers are the “backbone” of the flexible packaging industry, although a variety of papers, fabrics, and metallic foils are also employed. Almost without exception, high molecular weight polymers are physiologically inert and, therefore, pose no toxicological problems in themselves. However, monomers and low molecular weight fractions that may be incorporated in certain commercial polymers can be a source of concern, as can be other low molecular weight chemicals purposely added to commercial polymers, in some instances, to modify their processing or functioning characteristics. Conditions of use must also be considered when employing polymeric films (with or without additives) as the food contact components of packages. A polymer may be completely nontoxic and an adequate barrier to other package constituents when used to contain foodstuffs if the resultant package is subsequently stored at room temperature, under refrigeration, or frozen. However, when used as the inner ply of a boil-in pouch, a retortable pouch, or an oven bag, it must be determined that it is not subject to some degree of thermal breakdown or allows permeation of adhesive or ink components not approved for direct contact with food. Finally, if there is a requirement to sterilize packages before filling, as in aseptic packaging, the effect of the sterilizing medium on the packaging material must be fully understood.

Microphase separation of short wormlike diblock copolymers with a finite interaction range

Soft Matter ◽  
2016 ◽  
Vol 12 (8) ◽  
pp. 2481-2490 ◽  
Author(s):  
Ying Jiang ◽  
Xinghua Zhang ◽  
Bing Miao ◽  
Dadong Yan ◽  
Jeff Z. Y. Chen
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Structural Properties ◽  
Diblock Copolymers ◽  
Microphase Separation ◽  
Low Molecular Weight ◽  
Interaction Range ◽  
High Molecular Weight Polymers

A study on the structural properties of low-molecular weight AB diblock copolymers indicates substantial deviations from the properties of high-molecular weight polymers.

The Effect of Dextran of Various Molecular Weight on the Coagulation in Dogs

1961 ◽  
Vol 06 (01) ◽  
pp. 015-024 ◽  
Author(s):  
Sven Erik Bergentz ◽  
Oddvar Eiken ◽  
Inga Marie Nilsson
Keyword(s):  
Molecular Weight ◽  
Body Weight ◽  
High Molecular Weight ◽  
Bleeding Time ◽  
Factor Vii ◽  
Low Molecular Weight ◽  
Factor V ◽  
Coagulation Mechanism ◽  
Coagulation Defects

Summary1. Infusions of low molecular weight dextran (Mw = 42 000) to dogs in doses of 1—1.5 g per kg body weight did not produce any significant changes in the coagulation mechanism.2. Infusions of high molecular weight dextran (Mw = 1 000 000) to dogs in doses of 1—1.5 g per kg body weight produced severe defects in the coagulation mechanism, namely prolongation of bleeding time and coagulation time, thrombocytopenia, pathological prothrombin consumption, decrease of fibrinogen, prothrombin and factor VII, factor V and AHG.3. Heparin treatment of the dogs was found to prevent the decrease of fibrinogen, prothrombin and factor VII, and factor V otherwise occurring after injection of high molecular weight dextran. Thrombocytopenia was not prevented.4. In in vitro experiments an interaction between fibrinogen and dextran of high and low molecular weight was found to take place in systems comprising pure fibrinogen. No such interaction occurred in the presence of plasma.5. It is concluded that the coagulation defects induced by infusions of high molecular weight dextran are due to intravascular coagulation.

SYNTHESIS OF ISOTOPICALLY LABELLED OLEFINS VIA THE WITTIG REACTION

1965 ◽  
Vol 43 (5) ◽  
pp. 1614-1624 ◽  
Author(s):  
J. G. Atkinson ◽  
M. H. Fisher ◽  
D. Horley ◽  
A. T. Morse ◽  
R. S. Stuart ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Wittig Reaction ◽  
Low Molecular Weight ◽  
Phosphonium Salts ◽  
Reaction Conditions ◽  
Selective Labelling ◽  
Wittig Reactions

A new application of the Wittig reaction to the preparation of olefins of low molecular weight which allows selective labelling in the vinyl or allyl positions with isotopes of hydrogen and carbon has been developed. Using the modification of the Wittig reaction introduced by E. J. Corey, in which a solution of the methylsulfinyl carbanion in dimethyl sulfoxide serves as the base, a series of olefins from C2 to C8 were synthesized. The synthesis was applied to the preparation of the following labelled compounds: 5-methylene-14C-bicyclo[2.2.1]hept-2-ene; propene-1-14C; 1-butene-1-14C; propene-1-d1; 2-methylpropene-1,1-d2; 2-methyl-d3-propene-3,3,3-d3; 2-methyl-2-butene-4,4,4-d3; 2-methyl-d3-2-butene-1,1,1-d3; methylene-d2-cyclohexane. For the synthesis of carbon-labelled olefins the reaction has few limitations since the intermediates and products are isotopically stable under the reaction conditions. Deuterium-labelled olefins can be obtained from deuterated formaldehyde or β-deuterated phosphonium salts, but α-deuteroketones and aldehydes and α-deuterophosphonium salts lose the isotope to the solvent.In all the Wittig reactions, benzene was formed as a by-product in 10–15% yield. The mechanism of benzene formation is probably analogous to that proposed by Seyferth involving the decomposition of a pentacovalent phosphorous intermediate.

scholarly journals Antiparasitic antibodies occur with similar frequency in patients with clinically established multiple sclerosis with or without oligoclonal bands in the cerebrospinal fluid

2013 ◽  
Vol 71 (8) ◽  
pp. 512-515 ◽  
Author(s):  
Fabiana Cruz Gomes da Fonseca-Papavero ◽  
Dagoberto Callegaro ◽  
Paulo Diniz da Gama ◽  
Jose Antonio Livramento ◽  
Adelaide Jose Vaz ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Molecular Weight ◽  
High Molecular Weight ◽  
Hygiene Hypothesis ◽  
Oligoclonal Bands ◽  
Parasitic Infections ◽  
Low Molecular Weight ◽  
Serum Samples ◽  
Similar Frequency ◽  
Electrophoresis Of Proteins

The "hygiene hypothesis" postulates an inverse relationship between the prevalence of parasitic infections and the frequency of multiple sclerosis (MS). Objective: It was to study whether antibodies against parasites could be demonstrated more frequently in blood serum from MS patients with oligoclonal bands (OCB) than from MS patients without OCB. Methods: We studied serum samples from 164 patients who had previously been analyzed to investigate OCB. Parasitic antibodies were studied through unidimensional electrophoresis of proteins on polyacrylamide gel against Taenia antigens, searching for antiparasitic specific low molecular weight antibodies and also for antiparasitic nonspecific high molecular weight antibodies. Results: Two of the 103 patients with no evidence of OCB had antibodies of low molecular weight and 59 of them had antibodies of high molecular weight. Of the 61 patients with evidence of OCB, one showed antibodies of low molecular weight and 16 showed antibodies of high molecular weight. Conclusion: Antiparasitic antibodies are detected with similar frequency in MS patients with OCB and in MS patients without OCB.

Determination of Peroxides in Synthetic Rubbers

1945 ◽  
Vol 18 (4) ◽  
pp. 874-876
Author(s):  
Richard F. Robey ◽  
Herbert K. Wiese
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Quantitative Determination ◽  
High Molecular Weight ◽  
Active Oxygen ◽  
Lower Molecular Weight ◽  
Synthetic Rubber ◽  
High Molecular Weight Polymers ◽  
Methanol Solutions

Abstract Peroxides are found in synthetic rubbers either as the result of attack by oxygen, usually from the air, or as a residue from polymerization operations employing peroxide catalysts. Because of possible detrimental effects of active oxygen on the properties of the rubber, a method of quantitative determination is needed. The concentration of peroxides in substances of lower molecular weight may be determined with ferrous thiocyanate reagent, either titrimetrically as recommended by Yule and Wilson or colorimetrically as by Young, Vogt, and Nieuwland. Unfortunately, many highly polymeric substances are not soluble in the acetone and methanol solutions employed in these procedures. This is also the case with hydrocarbon monomers, such as butadiene, containing appreciable concentrations of soluble high molecular weight polymers. Bolland, Sundralingam, Sutton and Tristram recommended benzene as a solvent for natural rubber samples and the reagent made up in methanol. However, most synthetic rubbers are not readily soluble even in this combination. The following procedure employs the ferrous thiocyanate reagent in combination with a solvent capable of maintaining considerable concentrations of synthetic rubber in solution. The solvent comprises essentially 20 per cent ethanol in chloroform.

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