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Possible structures for the products obtained on alkali treatment of polyacrylonitrile are considered. The Pariser-Parr-Pople (PPP) self-consistent field method was applied to give A, , values for the proposed structures. The colouration of PAN by alkali was found to occur in two stages. There is a temporary colour which is destroyed by acids and a permanent colour which is not. The colour of alkali treated PMAN is entirely destroyed by acids. This temporary colouration may arise from n+x* transitions. We believe that the permanent colour of degraded PAN arises from x+n* transitions via a free radical activition mechanism and use of molecular oxygen.

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