Terpolymerization was investigated by dilatometry for zincacrylate (ZnA2), acrylonitrile (AN), and styrene (St), radically initiated by a As2S3-styrene complex (1) in dimethyl sulphoxide (DMSO), at 90 +/- 0.1-degrees-C for 1 h under inert atmosphere. The system follows non-ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is R(p)alpha(I)0.27(St)031(AN)0.22[ZnA2]0.12. The value for the activation energy and k(p)2/k(t) are 55 kJ mol-1 and 1.87 X 10(-7) 1 mol-1 s-1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.