Pyrolysis of polyacrylonitrile and related polymers—VIII. Copolymers of acrylonitrile with vinyl acetate,vinyl formate,acrolein and methyl vinyl ketone

Vinyl acetate exerts some blocking effect on the nitrile group oligomerization which dominates the initial pyrolytic processes in polyacrylonitrile, but the other comonommes studied allow more extensive nitrile reaction and do not effectively block the reaction. Decomposition of the vinyl esters, taking place concurrently with the nitrile reaction, tends to obscure any interaction with the nitrile reaction. Acrolein and methyl vinyl ketone do participate in the cyclization reactions and the former exhibits a small accelerating influence. The bulkiness of the comonomer appears to be an important factor in determining the thermogravimetric behaviour of the polymers. Thus vinyl acetate and methyl vinyl ketone copolymers are more liable to chain scission and fragmentation during the initial stages of pyrolysis than the vinyl formate and acrolein copolymers. These different behaviours are discussed in terms of the effect of the stereochemistry of the comonomer unit on the chemistry of the interaction between the comonomer structure and the propagating nitrile reaction.