Mechanical shear degradation of polyisobutylene, polystyrene, poly(viny1 chloride), poly-(methyl methacrylate), poly(decy1 methacrylate), poly(methy1 acrylate), and 1,4-polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants ki for the corresponding molecular weight distribution fractions Mi. GPC calibration via the concept of universal calibration, Mark-Houwink relations for polyisobutylene, poly(methy1 methacrylate), poly(methy1 acrylate), I ,4-polybutadiene, and poly(dimethylsi1oxane) in T H F as solvent had to be established for this purpose. Substantial differences in the rate constants ki were observed as a function of Mi, whereas a master curve resulted for all polymers except I ,4-polybutadiene when ki was plotted against the number of main chain carbon atoms ii for each molecular weight Mi. From this the shear degradation of C-C single bond polymers can be represented by ki = C . if, C being independent of the chemical nature of the C-C single bond polymer, and a varying from I ,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers. a) Teil 2: cf. 2 5 ) . b, Jetzige Adresse: Bayer AG Leverkusen, Abt. FE-DPP-PA, 5090 Leverkusen. 0025-1 I6X/8