2-(2-cyano-2-propyl)-1,3,5-triphenyl-1,2,5,6-tetrahydro-1,2,4,5-tetrazine dissociating into 1,3,5-triphenylverdazyl (TPV) and 2-cyano-2-propyl radical on heating was employed as the unimolecular initiator for the "living" free radical polymerization of styrene in the hope that TPV can be the mediator for the living polymerization. The polymerization followed first order kinetics with respect to styrene and the (M) over bar(n) of the resultant polymer increased with increasing conversion. However, the contents of end groups and (M) over bar(w)/(M) over bar(n), of the polymers indicated that the propagating radicals reversibly coupled with TPV and a rapid decrease in the TPV concentration arising from thermal decomposition allows concurrence of bimolecular termination leading to (M) over bar(w)/(M) over bar(n) > 1.5.