A study of the origins of colour in alkali degraded polyacrylonitrile and polymethacrylonitrile, 3. Computer predicted structures for the degradation products

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 λmax 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 → π* transitions. We believe that the permanent colour of degraded PAN arises from π→π* transitions via a free radical activition mechanism and use of molecular oxygen.