Distributed midpoint chain scission in ultrasonic degradation of polymers

The ultrasonic degradation of poly(bisphenol A carbonate), poly(epsilon-caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observedfor all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. (C) 2004 American Institute of Chemical Engineers.