Chain rupture

Figure 2-11. A modification chain—rupture discs below relief valves.

Chain scission is the ultimate fate of a stressed bond. At some value below the critical stress for chain rupture, bond angle deformation may result in an increase in reactivity. As stated in Sect. 3.1, mechanically activated hydrolysis of polymers containing ester groups can lead to the scission of the bond this concurrent reaction should be differentiated from homolytic chain scission, for example by looking at any pH-dependence as was found to be the case during shear degradation of DNA [84]. 

By analogy to simple olefins, we propose that 0(3P) initially adds to the 1,4 or 1,2 double bonds in polybutadienes at ambient temperature. Since the rate constants for 0(3P) addition to cis-2-butene and 1-butene (as models for 1,4 and 1,2 double bonds, respectively) are in the ratio 4.2 1 at 298 K ( 6), preferential addition to the 1,4 double bonds is assumed to persist to very high vinyl contents (-8011). The biradical adducts then rearrange to epoxides and carbonyl compounds or give rise to chain rupture and/or crosslinking as a consequence of PIF, according to the scheme ... 

This opened the possibility of ascertaining quantitative characteristics in the numerous individual reactions comprising the complex mechanism of oxidative chain reactions. Thus, rate constants have been determined for reactions with respect to their initiation and the branching, extension, and chain rupture, establishing specific details concerning the influence of solvents, reaction vessel surfaces, and other factors on the mechanism of individual reactions. Results of these investigations have... 

As oxidation processes were clarified, it was observed in other chain extension reactions that R02 radicals reacted with oxidation products hydroperoxides, alcohols, and ketones. The high reactivity of hydroperoxides and alcohols strongly influences the mechanism of oxidation processes. Chain rupture results from recombination of R02 radicals. 

Mastication of natural rubber with elastomers which do not give gel allows the synthesis of soluble graft or block copolymers, depending on the tendency for chain rupture and transfer reactions. 

At the same time, the above mentioned chain-like structure leads to the fact that different parts of polymer molecules fluctuating in space cannot go through each other without chain rupture. For the system of non-phantom closed chains, this fact means that only those space conformations that can be transformed continuously into one another are available (see Fig. 1). The adequate mathematical language for description of those physical effects is elaborated in the mathematical discipline called topology. That is why we also call the effects connected with chain uncrossability the topological constraints. 

PE Random chain rupture Waxes, paraffin oils, a-olefins Gases and light oils... 

The oxidation chemistry of small, partially-oxygenated fuels is of great interest in combustion chemistry as these are important intermediates in the combustion of virtually all commercial hydrocarbon fuels. Fuels with long carbon backbones react in their early stages mainly through a sequence of reactions that cause chain rupture, yielding smaller hydrocarbon fragments such as radicals. These then typically react with O2 to produce precursors of aldehydes, ketones etc. Not all of the features of acetaldehyde chemistry are completely representative of hydrocarbon oxidation, but this point is developed in the next chapter. 

Alkali metal naphthalene complexes have also been used to initiate epoxide polymerizations. Solov yanov and Kazanski [25] studied the polymerization of EO in tetrahydrofuran using sodium, potassium or cesium naphthalene as initiator. A living polymer was produced there is no chain rupture or transfer. The rate of polymerization depends on the concentration of active centres in a complex manner. The kinetic order varies from 0.23 for Na" (or 0.33 for K and Cs" ) up to full first order as initiator concentration decreases. The polymerization is first order in monomer, but deviations are observed at high concentrations. 

Reference to Tables 1 and 2 shows that the primary radicals invariably arise from main chain rupture, when radicals are produced by mechanical degradation. When irradiation is employed, primary radicals can also arise from the removal of side groups attached to the main chain. It is evident, therefore, that primary radical formation in mechanical degradation is always attributable to the polymer network being stretched sufficiently to rupture the chains, rather than molecules sliding over each other to strip off side groups. 

This synthesis cannot be used for making aluminum derivatives with any desired chain length because dehydroalumination reactions cause chain rupture ... 

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