Abstract On the example of oxidative polymerization of styrene, explored was the feasibility of regulating the length of polymer chain upon variation in the amount of oxygen dissolved in the liquid phase. Due to the use of rapidly decomposing 2,2′-azo-bis-(isobutyronitrile) (AIBN) as an initiator, the polymerization reaction (at 95 °С) proceeded in two stages. At the first one, a source of radicals was AIBN; while at the second stage, the peroxide groups formed in a course of reaction. Based on literature data for rate constants of elementary reactions, suggested was a mathematical model for calculating the running concentration of dissolved oxygen in reaction solution. At [AIBN] = 0.01 M and a rate of oxygen bubbling (VO2) of 62.4 × 10−3 M/min, the polymer exhibited a relatively low chain length (Мn = 700, Mw = 1600) but contained a large number of peroxide groups. Meanwhile, at [AIBN] = 0.05 M and VO2 = 6.0 × 10−3 M/min, the polymer chains were longer (Мn = 1700, Mw = 5800) while the amount of peroxide groups, low.