Styrene was polymerized with azobiscyanovaleric acid (ACVA) to obtain carboxy-telechelic polystyrene. Our aim was to synthesize an oligostyrene with a molecular weight of about 2000 g/mol. Thus, styrene was polymerized at 90 degreesC, where t(1/2ACVA) is very short, and at very high initiator concentrations. In these conditions a new termination reaction appeared, known as the primary radical termination (PRT). At first, PRT was observed by a deviation from the simple kinetic law. Then, the constant of PRT was determined by several kinetic models to be more important than the constant of bimolecular termination. Finally, the PREDICI simulation program was used to confirm the predominance of PRT. This simulation program allowed the determination of the constant of primary radical deactivation k(rr) and the influence of this reaction on the conversion rate.