Molecular weight reduction, modes

On the basis of the data at hand, we are currently considering two possible modes of molecular weight reduction. The first involves the generation of thermally weak bonds by the initial addition of hydrogen. We suggest that the addition of hydrogen to the structures below may be a key to the cleavage of critical bonds in coal. 

Fig. 14. A schematic mode) of the dissociation of earthworm hemoglobin induced by the reduction by hydrated electron. The molecule consists of 10 subunits with the total molecular weight of 4000000 [84]...

Apparently, AMSd is also useful in the reduction of the molecular weight of waste polymer.491 Heating polystyrene foam pieces recycled from food packaging materials at 160 °C for 1 h in the presence of AMSd reduced the Mn from approximately 70 000 to 10 000. The mode of action is unknown, but it is presumed that AMS radicals are generated and abstract hydrogen atoms from the polystyrene backbone, resulting in chain cleavage. 

First, temperature can determine the polymer state, that is, whether it is predominantly glassy, crystalline, elastic, or fluid. The specific temperatures for each state depend on composition and molecular weight. The softening of a polymer system, on raising the temperature, results in a lower stress and lower rate of energy input at a given shear rate. In consequence, there is a reduction in rupture and an increase in Thus, results at different temperatures are more similar and better compared at the same shear stress or rate of energy application. In many experiments, however, it has been easier to make the comparison at constant shear rate because of the mode of instrument operation. 

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