Link rupture

Kersey FR, Loveless DM, Craig SL. A hybrid polymer gel with controlled rates of cross-link rupture and self-repair. J R Soc Interface 2007 4 373-380. 

Once inside the metal/polymer structure the atomic hydrogen can either recombine to produce molecular hydrogen or reduce the chemical portion of the metal/polymer bondlo>l6. It should be borne in mind that the chemical portion of adhesion is not achieved until after the heat-treatment step. This step is performed subsequent to electroless deposition of the initial metal layer. Thus, as the hydrogen gas pressure increased, the weakest link ruptured and delamination of the metal from the polymer substrate occurred. 

Peroxide-induced cross-links are stable to oxidation, whereas sulfur cross-links may oxidize, leading to cross-link rupture. Peroxide-cured vulcanizates exhibit higher compression set resistance than their counterpart sulfur-cured vulcanizates. Peroxide vulcanizates generally have better low-temperature flexibility than do sulfur vulcanizates. 

However, too great a separation, and overdesign may oeeur. The overload eondition is represented by a unique stress, whieh is very mueh greater than the working stress, applied suddenly whieh eauses only the weak link to failure due to stress rupture. 

In the lightly cross-linked polymers (e.g. the vulcanised rubbers) the main purpose of cross-linking is to prevent the material deforming indefinitely under load. The chains can no longer slide past each other, and flow, in the usual sense of the word, is not possible without rupture of covalent bonds. Between the crosslinks, however, the molecular segments remain flexible. Thus under appropriate conditions of temperature the polymer mass may be rubbery or it may be rigid. It may also be capable of ciystallisation in both the unstressed and the stressed state. 

Several drugs in current medical use are mechanism-based enzyme inactivators. Eor example, the antibiotic penicillin exerts its effects by covalently reacting with an essential serine residue in the active site of glycoprotein peptidase, an enzyme that acts to cross-link the peptidoglycan chains during synthesis of bacterial cell walls (Eigure 14.17). Once cell wall synthesis is blocked, the bacterial cells are very susceptible to rupture by osmotic lysis, and bacterial growth is halted. 

F, the EF corner, and the FG corner to follow. These shifts are transmitted to the subunit interfaces, where they trigger conformational readjustments that lead to the rupture of interchain salt links. 

Among elastomers, artificial rubbers have replaced natural rabber for many uses because of their high resistance to chemical attack by ozone, an atmospheric pollutant. When ozone reacts with polymer chains, it breaks CUCn bonds and introduces additional cross-linking. Breaking 7r bonds causes the rabber to sofien, and cross-linking makes it more brittle. Both changes eventually lead to rupture of the polymer structure. 

Opening of the aromatic ring and further oxidation of the intermediates can happen in any of the aromatic intermediates formed. We assume that rupture of the C-C bond between the two carbons atoms linked to an OH group is easier because they are in a higher oxidation state. 

There are usually several reactors linked to a single catch tank. To ensure that rupture of a disk on one reactor does not affect the others, each reactor is fitted with a double-rupture disk assembly. The use of double-rupture disks in this application requires installation of a leak detection device in the space between the two disks. 

These partially contradictory observations give rise to the question whether the normal catabolism of Hp is related to the normal destruction of red cells or not. The Hp consumption secondary to erythrocyte destruction in a given person must reasonably depend upon the mechanism by which the red cells are destroyed. Neither in health nor in disease is the bulk of the red cell destruction due to intravascular rupture. A minor part of the cells may, however, rupture intravascularly, damaged cells may link Hp, and part of the Hb of the dying cells may be returned to plasma from die organs destroying red cells. 

The above reaction is rather remarkable in view of the un-leactivity of the fluorine atom in fluorobromoethane towards many reagents. In order to establish the identity of sesqui-fluoro-H , it was synthesized by an alternative unambiguous method (p. 130). Sesqui-fluoro-H is a mobile liquid, devoid of vesicant properties and non-toxic. The lack of toxicity is understandable since the animal body is probably unable to rupture this C—S link, and hence the compound cannot easily give rise to fluoroacetic acid. 

The ester group is then hydrolysed, and the hydrolysis normally stops at the MePO(OH)2 stage. More vigorous conditions are required to rupture the Me—P bond. Thus the normal hydrolysis product of D.F.P. and of tabun, namely, phosphoric acid, will give a positive test with ammonium molybdate, whereas the product from sarin, namely, methylphosphonic acid, will not respond to this test. Vigorous reagents such as hot nitric acid and ammonium persulphate will break the C—P link and then a positive test for phosphate is obtained with ammonium molybdate. Sarin can be prepared in a variety of ways. Three... 

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