Initiation of CN Oligomerization in PAN and Copolymers

Grassie and Hay first postulated a self-initiation mechanism which assumed the tertiary hydrogen in PAN to be sufficiently acid to initiate a nucleophilic attack on a CN group of the second-to-next monomer unit  

However, Grassie and McGuchan shifted emphasis in favor of a free radical process. 

The idea of self-initiation has by now been abandoned, in particular in view of the fact that the degradation reaction (disappearance of CN groups) exhibits no isotope effect, if poly-(a-deuteroacrylonitrile) is used instead of PAN (Petcavich et al. Grasselli et al. ). 

In the absence of ionic species (e.g. acidic comonomers such as itaconic acid or acrylic acid, or anionic additives such as alcoholates), the main initiation of the CN oligomerization in PAN and its copolymers is then, most probably, a radical 

From a theoretical point of view, a homolytic main chain scission is expected to be the first consequence of heat treatment. The main chain carbon-carbon bond in 

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