Reduction of nitrile end groups in styrene polymers and their subsequent determination by dye partition technique

Abstract

Nitrile groups were incorporated in polystyrene through (i) initiation with azoisobutyronitrile (AIBN) and (ii) copolymerization with a trace of acrylonitrile. Their detection and estimation by dye partition technique were experimentally realized. The method consists in first converting nitrile end groups to primary amino end groups (~CH₂NH₂) of by reducing with lithium aluminium hydride in tetrahydrofuran medium followed by testing and quantitatively estimating the amino end groups in the resultant polymer by the usual dye partition technique. AIBN initiated polystyrene was found to contain on the average 2 nitrile end groups per polymer molecule supporting the fact that combination is the predominant mode of termination in styrene polymerization. The copolymer reactivity ratio (r₁) for styrene (M₁) - acrylonitrile (M₂) copolymers as determined by this technique agrees fairly well with the existing literature values. This verifies the quantitative applicability of the dye partition method for the study of macromolecular reactions.