Contribution to the Study of the Vulcanization Reaction

1936 ◽  
Vol 9 (2) ◽  
pp. 201-205 ◽  
Author(s):  
Kurt H. Meyer ◽  
W. Hohenemser
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
Chemical Reaction ◽  
Low Molecular Weight ◽  
Sulfur Chloride ◽  
Chemical Combination

Abstract In spite of the great technical importance of vulcanization, the chemical reaction involved is not yet entirely understood, although at the present time it is assumed that chemical phenomena take part in this operation. To C. O. Weber in particular is due much of the research in the field of rubber. It was he who proved the chemical combination with sulfur. He assumed that during hot vulcanization, sulfur combines with two polyprene chains and that they unite chemically, but he was not able to go into this subject in more detail or to prove anything further. The process of cold vulcanization is better understood. There are good reasons for assuming that sulfur chloride reacts with the double bond of polyprene chains in the same way that it does with olefins of low molecular weight, for example with ethylene. It is known that sulfur chloride unites with this latter according to the following scheme:

scholarly journals Synthesis of a Chiral Meso-Like Ansa-Zirconocene Complex and its Use for the Catalytic Formation of Low Molecular Weight Polypropylene

1995 ◽  
Vol 50 (6) ◽  
pp. 982-989 ◽  
Author(s):  
Sven Thiele ◽  
Gerhard Erker ◽  
Cornelia Fritze ◽  
Christian Psiorz ◽  
Roland Fröhlich
Keyword(s):  
Crystal Structure ◽  
Molecular Weight ◽  
Double Bond ◽  
Ambient Temperature ◽  
Organic Synthesis ◽  
Crystal Structure Analysis ◽  
Low Molecular Weight ◽  
X Ray ◽  
Catalyst Systems ◽  
Double Bond Shift

Reaction of lithium(neomenthylcyclopentadienid) 3 with dimethyldichlorosilane gives dimethylbis[3-(neomenthyl)cyclopentadienyl]silane 4 regioselectively as a mixture of double bond shift isomers (57% isolated). Deprotonation with 2 equiv. of butyllithium followed by treatment with zirconiumtetrachloride furnished a mixture of the three {dimethylsilylenbis[η5-3-(neomenthyl)cyclopentadienyl][zirconium dichloride diastereomers from which the pure meso-like isomer 6e [p -R (1′S ,3 ′R ,4 ′R),p -S (1′S ,3 ′R ,4 ′R)] was isolated by fractional crystallization. Complex 6 c was characterized by an X-ray crystal structure analysis. Its D 1 - Zr - D 2 angle of 126.8° is very similar as observed in bis(η-cyclopentadienyl) zirconium dichloride (D 1 and D 2 denote the centroids of the cyclopentadienyl rings). The homogeneous 6c/methylalumoxane Ziegler-type catalyst produces polypropylene of low molecular weight (Mη ≈ 670 at ambient temperature). Related catalyst systems may find interesting applications in organic synthesis.

scholarly journals Ozonolysis of the double bond of the unsaturated uronate residue in low-molecular-weight heparin and K5 heparosan

2011 ◽  
Vol 346 (13) ◽  
pp. 1962-1966 ◽  
Author(s):  
Sayaka Masuko ◽  
Kyohei Higashi ◽  
Zhenyu Wang ◽  
Ujjwal Bhaskar ◽  
Anne Marie Hickey ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
Low Molecular Weight Heparin ◽  
Low Molecular Weight ◽  
Unsaturated Uronate

Sulfur Vulcanization of Simple Model Olefins, Part I: Characterization of Vulcanization Products of 2,3-Dimethyl-2-Butene

1992 ◽  
Vol 65 (2) ◽  
pp. 343-349 ◽  
Author(s):  
P. Versloot ◽  
J. G. Haasnoot ◽  
J. Reedijk ◽  
M. van Duin ◽  
E. F. J. Duynstee ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
Simple Model ◽  
1H Nmr ◽  
Low Molecular Weight ◽  
Rp Hplc ◽  
Sulfur Vulcanization ◽  
Weight Model

Abstract To study the mechanism of the sulfur vulcanization of rubber, 2,3-dimethyl-2-butene (C6H12) was used as a simple, low-molecular-weight model alkene. Only equivalent allylic positions are present in this alkene. Treating C6H12 with a mixture of ZnO, S8, and the accelerator tetramethylthiuramdisulfide at 140°C yields a mixture of addition products (C6H11—Sn—C6H11). RP-HPLC in combination with MS and 1H-NMR shows that the products differ only in the length of the sulfur bridge. Small quantities of isomerized products have been found, in which a 1,3-shift of the double bond has occurred.

scholarly journals Syntheses, Structures and Properties of Polycarbosilanes Formed Directly by Polymerization of Alkenylsilanes

1992 ◽  
Vol 271 ◽  
Author(s):  
John Masnovi ◽  
Xin Y. Bu ◽  
Kassahun Beyene ◽  
Paula Heimann ◽  
Terrence Kacik ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Structures And Properties ◽  
Weight Distributions

ABSTRACTVinylsilane polymerizes to form predominantly a carbosilane polymer using dimethyltitanocene catalyst. This is in contrast to alkylsilanes, which afford polysilanes under the same conditions. The mechanism of polymerization of alkenylsilanes has been shown to be fundamentally different from that for the polymerization of alkylsilanes. The silyl substituent apparently activates a double bond to participate in a number of polymerization processes in this system, particularly hydrosilation. Isotopie labeling indicates the involvement of silametallocyclic intermediates, accompanied by extensive nuclear rearrangement. Polymers and copolymers derived from alkenylsilanes have relatively high char yields even for conditions which afford low molecular weight distributions. Formation of crystalline β-SiC is optimum for a copolymer of an alkylsilane and an alkenylsilane having a silane/carbosilane backbone ratio of 85/15 and a C/Si ratio of 1.3/1.

The Formation of High Polymers by Condensation between Metallic Polysulfides and Dihalogenated Hydrocarbons and Ethers

1936 ◽  
Vol 9 (3) ◽  
pp. 373-382 ◽  
Author(s):  
J. C. Patrick
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
General Theory ◽  
Molecular Mass ◽  
High Molecular Weight ◽  
General Type ◽  
Low Molecular Weight ◽  
Linear Polymers ◽  
Bifunctional Compounds ◽  
Made In

Abstract The general theory of formation of high molecular weight linear polymers by condensation between bifunctional compounds of low molecular weight to form products of large molecular mass has been so thoroughly reported in the literature that no extensive citation is believed to be advisable here. A very thorough study of this type of reaction has been made by Carothers and his co-workers on the formation of polyesters, the reaction being of the general type: One can, without taxing the imagination, conceive of the polymerization of isoprene or butadiene as belonging to the same general type of phenomenon, differing only in the fact that the reacting molecules are alike instead of different and that the “condensate” is one double bond per molecule. Therefore, no attempt will be made in this paper to distinguish between condensation and polymerization. When organic dihalides having CH2X terminals, in which “X” denotes a halogen, are caused to react with metallic polysulfides, MSxM, there usually results a linear polymer of high molecular weight.

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
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