Flow Behavior of Low Molecular Weight Polybutadiene, Carboxyl‐Polybutadiene, and Butadiene‐Acrylonitrile Copolymers

1966 ◽  
Vol 10 (2) ◽  
pp. 545-570 ◽  
Author(s):  
Richard J. Boyce ◽  
Walter H. Bauer ◽  
Edward A. Collins
Keyword(s):  
Molecular Weight ◽  
Flow Behavior ◽  
Low Molecular Weight ◽  
Acrylonitrile Copolymers

Influence of Chemical Nature on Flow Behavior of Polymers. I. Shear Rate and Temperature Dependence

1970 ◽  
Vol 43 (5) ◽  
pp. 1109-1115 ◽  
Author(s):  
E. A. Collins ◽  
T. Mass ◽  
W. H. Bauer
Keyword(s):  
Molecular Weight ◽  
Shear Rate ◽  
Chemical Nature ◽  
Flow Behavior ◽  
Capillary Viscometer ◽  
Low Molecular Weight ◽  
Flow Activation Energy ◽  
Flow Activation ◽  
Made In ◽  
Low Shear

Abstract The flow behavior of low molecular weight liquid polybutadiene polymers was studied as a function of shear rate, temperature, and molecular structure. Measurements were made in the temperature range 15 to 50° C and shear rate range 1 to 15,000 sec−1 with a cone and plate and a capillary viscometer. Limiting low shear viscosity, flow activation energy, and critical shear rate marking onset of shear rate thinning were found to be strongly dependent upon the presence of functional groups such as hydroxyl, carboxyl, and nitrile. The modifying groups showed a greater effect than the molecular weight upon the properties measured.

Filler Reinforcement of Liquid Elastomers

1973 ◽  
Vol 46 (1) ◽  
pp. 161-177 ◽  
Author(s):  
D. Rivin ◽  
R. G. True
Keyword(s):  
Molecular Weight ◽  
Flow Behavior ◽  
Liquid Hydrocarbon ◽  
General Purpose ◽  
Chain Extension ◽  
Low Molecular Weight ◽  
Precipitated Silica ◽  
Polar Polymers ◽  
Reinforcing Fillers ◽  
Filler Reinforcement

Abstract To realize the potential processing benefits of liquid rubbers, methods must be developed for producing acceptable reinforced compounds which retain the inherent rheological advantages of the uncured polymer. The most promising commercially available liquid rubbers are functionally terminated low molecular weight analogs of common general-purpose elastomers such as poly-(butadiene) or butadiene copolymers. In principle, these low molecular weight polymers can be vulcanized by a combination of chain extension and cross-linking to yield vulcanizates comparable to those from solid elastomers. Both cure reactions can be carried out simultaneously with a chemically specific polyfunctional coupling agent, or alternatively, chain extension with a difunctional reactant can be followed by use of accelerated sulfur or equivalent crosslinking agents. In contrast to certain polar polymers, liquid hydrocarbon rubbers yield relatively weak vulcanizates which are unsuitable for mechanical and tire applications. Physical properties are greatly improved by addition of up to 60 phr of reinforcing fillers such as carbon black or precipitated silica, but at the expense of flow behavior. Important filler-dependent properties of representative liquid rubbers will be described, with emphasis on the rheology of reinforced compounds.

A high-performance oil-free backing pump for electron microscopes

1978 ◽  
Vol 36 (1) ◽  
pp. 110-111
Author(s):  
G.K.W. Balkau ◽  
E. Bez ◽  
J.L. Farrant
Keyword(s):  
Molecular Weight ◽  
Electron Microscope ◽  
Hot Spots ◽  
High Performance ◽  
Carbonaceous Material ◽  
Contamination Rate ◽  
Low Molecular Weight ◽  
Principal Source ◽  
Rotary Pumps ◽  
Electron Microscopes

The earliest account of the contamination of electron microscope specimens by the deposition of carbonaceous material during electron irradiation was published in 1947 by Watson who was then working in Canada. It was soon established that this carbonaceous material is formed from organic vapours, and it is now recognized that the principal source is the oil-sealed rotary pumps which provide the backing vacuum. It has been shown that the organic vapours consist of low molecular weight fragments of oil molecules which have been degraded at hot spots produced by friction between the vanes and the surfaces on which they slide. As satisfactory oil-free pumps are unavailable, it is standard electron microscope practice to reduce the partial pressure of organic vapours in the microscope in the vicinity of the specimen by using liquid-nitrogen cooled anti-contamination devices. Traps of this type are sufficient to reduce the contamination rate to about 0.1 Å per min, which is tolerable for many investigations.

Low-molecular-weight heparin in the prevention and treatment of thromboembolic disorders

1998 ◽  
Vol 1 (5) ◽  
pp. 166-174 ◽  
Author(s):  
Evelyn R Hermes De Santis ◽  
Betsy S Laumeister ◽  
Vidhu Bansal ◽  
Vandana Kataria ◽  
Preeti Loomba ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Low Molecular Weight Heparin ◽  
Low Molecular Weight ◽  
Prevention And Treatment

Venous thromboembolism in a general hospital. An update with low molecular weight heparin prophylaxis

VASA ◽  
2007 ◽  
Vol 36 (1) ◽  
pp. 17-22
Author(s):  
Schulz ◽  
Kesselring ◽  
Seeberger ◽  
Andresen
Keyword(s):  
Molecular Weight ◽  
Pulmonary Embolism ◽  
Venous Thromboembolism ◽  
Low Molecular Weight ◽  
Trauma Patients ◽  
Vte Prophylaxis ◽  
Vein Thrombosis ◽  
Patients At Risk ◽  
Hospital Stays ◽  
Event Rates

Background: Patients admitted to hospital for surgery or acute medical illnesses have a high risk for venous thromboembolism (VTE). Today’s widespread use of low molecular weight heparins (LMWH) for VTE prophylaxis is supposed to have reduced VTE rates substantially. However, data concerning the overall effectiveness of LMWH prophylaxis is sparse. Patients and methods: We prospectively studied all patients with symptomatic and objectively confirmed VTE seen in our hospital over a three year period. Event rates in different wards were analysed and compared. VTE prophylaxis with Enoxaparin was given to all patients at risk during their hospital stay. Results: A total of 50 464 inpatients were treated during the study period. 461 examinations were carried out for symptoms suggestive of VTE and yielded 89 positive results in 85 patients. Seventy eight patients were found to have deep vein thrombosis, 7 had pulmonary embolism, and 4 had both deep venous thrombosis and pulmonary embolism. The overall in hospital VTE event rate was 0.17%. The rate decreased during the study period from 0.22 in year one to 0,16 in year two and 0.13 % in year three. It ranged highest in neurologic and trauma patients (0.32%) and lowest (0.08%) in gynecology-obstetrics. Conclusions: With a simple and strictly applied regimen of prophylaxis with LMWH the overall rate of symptomatic VTE was very low in our hospitalized patients. Beside LMWH prophylaxis, shortening hospital stays and substantial improvements in surgical and anasthesia techniques achieved during the last decades probably play an essential role in decreasing VTE rates.

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