The living free radical polymerization of styrene was studied with benzoyl peroxide as the initiator in the presence of TEMPO (2

2

6

6-tetramethylpiperidinyl-1-oxy)．It was found that styrene polymerization was distinctly accelerated by means of using malononitrile (MN) as additive．The purpose of this paper is to explore the effect of MN／bpy On the control of molecular weight．These mixture additives were able to control the polymerization of styrene to high conversion (85％) in 4 hours

and samples of molecular weight from 1×104 to 9×104 and with polydispersities of 1.15 to 1.4 were readily obtained．In comparison with the polymerization without any additives

these systems represented a dramatic improvement in the ability to control the molecular weight．The molecular weight of the polymer gradually increased with time

while the narrow molecular weight distribution remained unchanged．The molecular weight evolved in a nearly linear fashion with increasing conversion．Using a 1:1.2 molar mixture of BPO and TEMPO with [Bpy]／[TEMPO]=2／1

[MN]／[TEMPO]=2.5

the conversion of the polymerization at 135℃ reached 85％ in 4 hours

and the polydispersity was below 1.5

and the difference between the theoretical molecular weight and the experimental molecular weight was controlled below 20％．