Oxygen-ascorbic acid-ferric ion initiating system. Kinetics of polymerization of methyl methacrylate

Abstract

The kinetics of polymerization of methyl methacrylate (MMA) in dilute nitric acid medium at 40°C initiated by the three component initiating system, oxygen-ascorbic acid (AA)-ferric ions was investigated. The rate of polymerization, R_p, was found to be proportional to [MMA]^1.5 under different experimental conditions. R_p, was independent of [Fe³⁺] in the concentration range 2 to 5-10⁻⁵ M, but decreased slightly at higher values. R_p was also independent of [AA] and a dependence on [O₂]^0.6 was noticed with [O₂] <6.5×10⁻⁴M. After an initial increase, R_p became independent above [HNO₃] ≈ 0.3M. Ionic strength, μ, of the medium had no effect on R_p. A rate increase up to 42°C followed by constancy and decrease with further increase in temperature (>46°C) was noticed. The chain lengths of the polymers were determined to be in the range 10²-10³ by viscometry. A plausible reaction mechanism with initiation by the primary radical and termination by mutual interaction was proposed.