Nonrandom scission

Mechanism. Although there is still some debate about the precise origin of scission, it has been shown that ultrasound-induced polymer breakage is a direct consequence of cavitation, because under conditions that suppress cavitation, no degradation is observed. In this nonrandom scission process the poisoner is fractured at the centre of the chain (54-56). This is clearly shown in Figure 11,... 

According to Fukutomi et al. [54], the process of polymer degradation in solution by capillary flow is influenced by concentration. The tendency toward nonrandom scission increases as the polymer concentration decreases. In this perspective, it is not surprising that there is uncertainty and disagreement concerning the location of bond ruptures. 

Whereas the cleavage of /S-poly(L-malate) at neutral pH is at random [2], alkaline hydrolysis reveals characteristic patterns of the cleavage products, which is due to nonrandom chain scission (Fig. 3). The phenomenon is explained by an autocatalytic ester hydrolysis. Assuming that one (or both) of the polymer ends bends... 

In terms of product properties, the molecular weight distribution is an important characteristic of polymers. In the polymer industry often a post-processing step is applied to alter the molecular weight of the polymers eg, the peroxide-induced degradation of polypropylene (53). In this process, fracture of the polymer chain occurs at a random site. An alternative method is ultrasound-induced polymer scission, which involves a much better controlled, nonrandom process (7). This enables a relatively straightforward production of the desired molecular weight as well as the formation of block copolymers, as described in the previous section. 

APP oxidizes more rapidly than IPP while APP undergoes a random scission, the oxidation of IPP is nonrandom [115b]. The induction period for IPP oxidation is longer and the maximum hydroperoxide concentration is lower than that of APP. 

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