Chain breakage

The presented results and the additional information taken from various references indicate the direct relevance of the size of the network strands for the crack opening displacement and consequently for the toughness of the polymer. In polymers under load, the molecular chains at the tip of the crack break after the deformation zone ahead of the crack has grown to a critical width 5C, that is the crack opening displacement. This value 5C is proportional to the length of the molecular strands of the network and is linked in this way to the molecular structure of the polymer. However, the molecular mechanism for chain breakage in the deformation zone is not known at present. 

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. 

Backbone chain scission degradation can be divided as occurring via depolymerization, random chain breakage, weak-link or preferential site degradation, or some combination of these general routes. In depolymerization, monomer is split off from an activated end group. This is the opposite of the addition polymerization and is often referred to as unzipping. ... 

The relationship between chain length and chain breakage was found to be directly related to the typical length of chain necessary to produce physical cross-links, i.e., chain... 

There are exceptions to this. One exception is UHMWPE, which has few chain entanglements so it is easier to pull long chains from a PE matrix without chain breakage. The equivalent energy necessary to pull a UHMWPE chain from a PE matrix occurs at about a chain length of 100,000 (or a DP of about 3,300), much larger than that for PS. 

Sklenar, H., Wiistner, D., Rohs, R. Using internal and collective variables in Monte Carlo simulations of nucleic acid structures chain breakage/closure algorithm and associated Jacobians. J. Comput. Chem. 2006, 27, 309-15. 

Thus in the instance of 1% solution exposed for an interval of 4 hr to the action of light the decrease in viscosity is 0.3-0.7%. With 10-20% solutions, on the other hand, the reduction in viscosity during the same period is 25.0-34.2%. Mine s experiments showed that in solutions of low viscosity the reduction of viscosity could remain unobserved. Claesson and Wettermark [92a] investigated the irradiation of solutions of cellulose nitrate with light of wave-length 253 rafi. The depolymerization was followed viscosimetrically and the chain breakage was found to obey the course predicted theoretically for a random process with a quantum yield of 0.01-0.02. 

Ulanski P, Merenyi G, Lind J, Wagner R, von Sonntag C (1999) The reaction of methyl radicals with hydrogen peroxide. J Chem Soc Perkin Trans 2 673-676 Ulanski P, Bothe E, Hildenbrand K, von Sonntag C (2000) Free-radical-induced chain breakage and depolymerization of polyfmethacrylic acid). Equilibrium polymerization in aqueous solution at room temperature. Chem Eur J 6 3922-3934... 

Thermal degradation is generally accompanied by an exothermic reaction which may result from oxidation. Such a reaction can easily be detected in a DSC output. By further warming of the test sample, cross-linking may take place and, finally, chain breakage, as shown in Fig. 2.22. 

In real systems the formation of thermodynamically stable carbon structures having the minimum surface energy is inevitably accompanied by the separation of the elements that are excessive for some reasons due to chain breakage, energetic or steric misfit, etc. Besides, semiproducts that are readily soluble in benzene enter... 

In summary, the elimination of superoxide from hyaluronic-acid peroxy radicals is clearly important and may lead to chain breakage. Some possible... 

Force for chain breakage Surface density of entangled chains... 

Lindahl T, Andersson A. Rate of chain breakage of apurinic sites in double-stranded DNA. Biochemistry 1972 11 3618-3623. 

---