Polyisobutene Degradation in Laminar Flow: Composition and Shear Variables

The mechanical degradation of polyisobutene solutions in laminar flow under known shear stress conditions was performed in a thin-film, high-shear, rotational viscometer. Polyisobutenes with molecular weights from 40 000 to over a million were studied at several temperatures and concentrations in n-hexadecane. Reduced variables, of a form similar to those used in studies of temporary viscosity losses, can be used successfully to correlate permanent viscosity losses due to degradation. The variables which superimpose are stress, temperature, and concentration. The range in which reduced variables apply corresponds to concentrations and molecular weights where degradation is commonly observed and to the region where polymer entanglements exist.