Chain scission determination

It may be noted that chain scission determination is actually of an extremely high sensitivity not reached by many of the new instrumental methods. One rupture in every ten original chains can be determined by very simple means. Such scission represents an extremely small chemical reaction. 

In transient elongational flow degradation, it was determined in the authors laboratory, by a detailed mass balance, that main chain scission accounted for >95% of the degradation in dilute solution. Any other type of depolymerization, if present, should then be of minor importance. 

On replication, insertion or deletion of bases may occur. Chain scission and chromosome breaks are also possible. Quinacrine is useful in human cytogenetics, since it intercalates significantly into the heterochromatin of the Y chromosome, making it fluoresce and rendering it identifiable cytologically. Detection of the Y chromosome is important in prenatal sex determination. Other dyes present in our environment are potentially mutagenic. For example, some hair dyes were shown to be mutagenic for E. coli. 

The molecular weights of the polymers before and after irradiation were followed by GPC to determine changes in the molecular weights of the polyamides. It was found that photolysis of the polymer resulted in polymer chain scission, leading to the appearance of oligomers containing thymine bases at the end of the molecules. 

Methyl end groups resulting from main-chain scission in ethylene-propylene copolymers have observed by their characteristic 13C NMR resonance and determined quantitatively to give values of G(scission). 

Experimental determination of the quantum efficiency of photosensitive polymers of the sort that are used in one-component positive resist systems is a more complex experimental undertaking. Here the quantum efficiency is defined as the number of main chain scissions that occurs per photon absorbed. Guillet and coworkers at the University of Toronto have... 

So far we have only considered polymers that undergo main-chain scission upon exposure to radiation. PMMA is an example of such a material. If, on the other hand, one considers polymeric systems in which both scissioning and crosslinking events occur simultaneously upon exposure, the analysis depicted above will allow determination only of the net scission-... 

Scission yields are determined by stress relaxation measurements during irradiation of specimens. Permanent and temporary chain scissions are measured by this technique in contrast to gel measurements, which provide data only on permanent scissions. 

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