Breakage monomer

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. ... 

Unlike the carbonyl linkage, the carbon-carbon double bond undergoes polymerization by both radical and ionic initiators. The difference arises because the re-bond of a vinyl monomer can respond appropriately to the initiator species by either homolytic or heterolytic bond breakage ... 

Sonication, the application of high-intensity ultrasound at frequencies beyond the range of human hearing (16 kHz), of a monomer results in radical polymerization. Initiation results from the effects of cavitation—the formation and collapse of cavities in the liquid. The collapse (implosion) of the cavities generates very high local temperatures and pressures. This results in the formation of excited states that leads to bond breakage and the formation of... 

Figure 23.1. Schematic illustration of direct reversal of a pyrimidine dimer by the enzyme DNA photolyase. The enzyme binds to the pyrimidine dimer present in DNA. The square and triangle represent the two noncovalently bound chromophores that are present in all photolyases. The chromophores harness the energy of photoreactivating blue wavelengths of light and use them to catalyze the breakage of the pyrimidine dimer back to adjacent monomers. [Adapted fromFriedberg, E. C., Walker, G. C., Siede, W., Wood, R. D., Schultz, R. A., and Ellenberger, T. (Eds.). DNA Repair and Mutagenesis, 2nd ed., ASM, Washington, D.C., 2006.]...

The breakage of the polymer chain is the most probable at the allyl position to double bonds, forming primary macroradicals in unsaturated hydrocarbon chain polymers. The deplacement of the primary radical site is carried on through the rearrangement of the C=C double bonds, producing monomer or cyclic dimer and reproducing the primary macroradicals (4 and 5) according to Scheme 12.4. 

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