Simultaneous chain scission

According to these results, we proposed the following mechanism of degradation by hydrolysis which involves simultaneous chain scissions and ftulher depolymerization together with ester group hydrolysis (Figure 8). 

The in vitro hydrolysis study, by means of potentiometry, weight loss, SEC and NMR, shows that the degradation mechanism involves simultaneous chain scissions and ester group hydrolysis. Indeed, ester hydrolysis was evidenced by the release of an acidic group as glyoxylic acid hydrate by NMR, or by the drop of pH and the loss of ethanol (weight loss and NMR). The decrease in molecular weight observed by SEC and the presence of small molecules by NMR prove that chain scissions occurred at the same time. 

Moore [105] has shown that irradiation of polyamides at wavelengths below 300 nm results in simultaneous chain scission and crosslinking. Analysis of the products obtained after hydrolysis of irradiated polyamide suggests that chain scission proceeds according to reactions (8) and (9), similar to the Norrish type I and type II reactions of ketones, the former being preponderant ... 

Cross-linking induces an increase in the glass transition temperature. In the case of simultaneous chain scission and cross-linking, it can be written, in a first approach, that ... 

The gas-phase polymerization in the presence of radiation doses in the range of 10-60 Mrad have been studied. The tacticity of the polymer was found to be independent of the polymerization temperature [184]. Upon irradiation of PVC with an electron beam, the polydispersity of the resin increases due to simultaneous chain scission and cross-linking [185]. 

During simultaneous chain scission and crosslinking reactions two cases must be considered [524] ... 

Poly(vinyl acetate) (3.38) undergoes simultaneous chain scission and cross-linking when UV irradiated (254 nm). At the same time its absorption spectrum (Fig. 3.23) shows the formation of short sequences of conjugated double bonds, i.e. trienes. 

The effects of UV irradiation on these polymers differs significantly. Polyacrylates are simultaneously chain scissioned and crosslinked, whereas polymethacrylates have no tendency to form crosslinks when irradiated. 

Silane copolymers which contain dimethysilane units (4.96) are rapidly photodegraded under UV irradiation [173,2330], When the copolymers were irradiated in an argon atmosphere some crosslinking took place with simultaneous chain scission. Copolymers with aryl groups attached to silicon undergo more photocrosslinking in argon than those without aryl substituents ... 

The intensity of radiation absorbed required for gel formation (/g), in the absence of simultaneous chain scission, is given by ... 

Summary of governing equations for simultaneous chain scission and crystallisation... 

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