A comprehensive kinetic model is developed for the suspension free-radical polymerization of vinyl chloride (VC) initiated by a mixture of monofunctional and bifunctional initiators. The model predicts the monomer concentrations in the gas, aqueous, and polymer phases; the overall monomer conversion; the polymerization rate; the polymer chain structural characteristics (e.g., number-and weight-average molecular weights, short chain branching, and number of terminal double bonds); the reactor temperature and pressure; and the coolant flow rate and temperature in the reactor's jacket over the whole batch polymerization cycle. The capabilities of the model are demonstrated by a direct comparison of model predictions with experimental data on monomer conversion, number-and weight-average molecular weights, and reactor pressure. It is shown that high molecular weights and high polymerization rates can be obtained in the presence of a mixture of monofunctional and bifunctional initiators. Moreover, the use of bifunctional initiators results in a significant reduction of the polymerization time without impairing the final molecular weight properties of the polymer. To our knowledge, this is the first comprehensive kinetic modeling study on the combined use of monofunctional and bifunctional initiators on the free-radical suspension polymerization of VC. Taking into consideration the excellent agreement of the model predictions with the experimental measurements, the proposed model should find wide application in the design, optimization, and control of industrial poly(vinyl chloride) batch reactors.

A comprehensive mathematical model is developed for the free-radical copolymerization of ethylene with various comonomers (e.g., vinyl acetate, methyl or ethyl acrylate, and acrylic or methacrylic acid) in high-pressure tubular reactors. Polar copolymers usually exhibit lower crystallinity and yield strength than low-density polyethylene grades and are used for applications requiring flexibility, toughness, stress-cracking resistance, and adhesion to coatings. In the present study, a detailed kinetic mechanism is proposed to describe the molecular and compositional developments in the free-radical copolymerization of ethylene with a comonomer. On the basis of the postulated kinetic mechanism, a system of differential mass balance equations are derived for the various molecular species, total mass, energy, and momentum in the polymerization system. The model equations are coupled with a set of algebraic equations for estimating the thermodynamic and transport properties of the reaction mixture. The number and weight molecular weight and copolymer composition averages, short-and long-chain branching frequencies, etc., are calculated in terms of the leading moments of the bivariate number chain-length distributions of "live" and "dead" copolymer chains. The predictive capabilities of the mathematical model are demonstrated by a direct comparison of the model predictions with industrial experimental data on the reactor temperature profile and pressure, the overall monomer conversion, and the final molecular and compositional properties of copolymers. Simulation and experimental results are presented for different copolymer grades including ethylene-ethyl acrylate, ethylene-methyl acrylate, and ethylene-vinyl acetate copolymers.