Thermal field-flow fractionation of initially dilute polymer solutions as a shear degradation model. Scaling model of macromolecule degradation at concentrations exceeding the critical entanglement value

Experimental data are presented on thermal field-flow fractionation (TFFF) of anionic polystyrene (PS) samples in the range M = (4-12).10(6). They sho w extensive degradation of macromolecular chains at relatively low rate gra dients (G < 30 s(-1)). The possibility of the influence of relaxation effec ts on the shape of fractograms and the elution volumes of the samples was t aken into account. Mean concentrations in accumulative zones were evaluated . It was shown that, in all cases when degradation was observed, the accumu lative zones are the layers of entangled macromolecules. The use of the sca ling approach made it possible to simulate layer extension toward the chann el center under the influence of the rate gradient. It was shown that, duri ng stretching, the layer is destroyed into blobs, the size of which is dete rmined by experimental conditions. An expression for the critical gradient leading to layer degradation was derived. Quantitative evaluations of fragm ent sizes and critical gradients obtained from the model are in good agreem ent with experimental data. The model developed for specific experimental c onditions confirms the proposed general mechanism of the so-called shear de gradation of macromolecules. The physical picture of degradation in the TFF F channel was considered.