The degradation of polystyrene in various Lewis acids [aluminum chloride, ferric chloride, boron triflouride etherate, and tin(IV) chloride] at different temperatures (75-125°C) has been studied in this work. The evolution of the molecular weight distribution (MWD) has been modeled using continuous distribution kinetics with a stoichiometric kernel for random chain scission. The degradation rate was the highest in the presence of aluminum chloride. The reactions were also carried out at different aluminum chloride concentrations, and the degradation rate was proportional to the fourth power of the Lewis acid concentration. The activation energy of polystyrene degradation in the presence of aluminum chloride, determined from the temperature dependence of the degradation rate coefficient, was 7.7 kcal/mol.
The degradation kinetics of polystyrene (PS) in supercritical benzene was studied at various
temperatures (300−330 °C) at 5.0 MPa. The time evolution of the molecular weight distributions
was obtained by analyzing the samples with gel permeation chromatography. The evolution
was modeled with continuous distribution kinetics by assuming that the degradation rate
coefficient varied linearly with molecular weight. The activation energy of the rate coefficient
was determined to be 13.8 kcal/mol. The degradation rate coefficients obtained in supercritical
benzene were substantially higher than the rate coefficients observed for degradation of PS in
subcritical solvents at high pressures and in solvents at normal pressures. This significant
enhancement in the degradation rate may be due to enhanced diffusivity in supercritical fluids.
Ultrasonic degradation of poly(methyl methacrylate) (PMMA) was carried out in several solvents and some mixtures of solvents. The time evolution of molecular weight distribution (MWD), determined by gel permeation chromatography, is analysed by continuous distribution kinetics. The rate coef®cients for polymer degradation are determined for each solvent. The variation of rate coef®cients is correlated with the vapour pressure of the solvent, kinematic viscosity of the solution and solvent±polymer interaction parameters. The vapour pressure and the kinematic viscosity of the solution are found to be more critical than other parameters (such as the Huggins and Flory±Huggins constants) in determining the degradation rates.
The degradation rate of a polymer mixture depends on the particular polymer mixture, and the presence of a second polymer can increase, decrease, or not affect the degradation rate of the first polymer. The degradation rates of poly(vinyl acetate) in both the presence and absence of polystyrene at various temperatures (220-250 °C) were experimentally determined. The molecular weight distributions of the polymers were obtained by analyzing the samples by gel permeation chromatography. Continuous distribution kinetics were employed for determining the degradation rates of binary polymer mixtures. The results indicated that, because of the interaction of mixed radicals with polymer by hydrogen abstraction, the degradation rates of poly(vinyl acetate) are considerably enhanced in the presence of polystyrene, while the degradation rate of polystyrene decreases.
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