Kinetics and Mechanism of Heterogeneous Graft Polymerization of Acrylonitrile onto Polyvinyl Alcohol Initiated with Ceric Ammonium Nitrate

A model for a heterogeneous graft polymerization of vinyl andlor acrylic monomers on polyvinyl alcohol (PVA) initiated by cent ions is developed. The model can be easily extended to other (poly)hydroxylic substrates. Graft copolymerization of acrylonitrile (AN) onto PVA was carried out using eerie ammonium nitrate (CAN) as an initiator in an aqueous nitric acid medium under N2 atmosphere. The optimum conditions for grafting were determined by studying the effects of concentrations of initiator, monomer, PVA and acid on the percentage of grafting. The graft copolymer was characterized by FTIR spectroscopoy. The graft yield increases with increasing monomer concentration up to 1.728 M, with further increases, the graft yield decreases. The graft yield increases with increasing initiator concentration up to 1.31x10-2 M and PVA up to 12 g/L and thereafter it decreases. The effects of the pH of polymerization medium, reaction time, temperature on graft yield have also been investigated. The kinetics of the graft polymerization of acrylonitrile onto PVA in aqueous solution was studied by bromornetry titration. The following rate expression: Rpak [AN] ' 06[CAN] 0.62[PVA] 0m was observed and a suitable mechanism is suggested. The overall activation energy of the copolymerization reaction is found to be 42.51 kJlmol within the temperature range 25—45 'C. Key Words: kinetics, graft copolymerization, polyvinyl alcohol, acrylonitrile, eerie ammonium nitrat