THE RELAXATION OF CONCENTRATED POLYMER-SOLUTIONS

The focus of this paper is on the viscoelastic properties of concentra ted polymer solutions and polymer melts. Dynamic mechanical measuremen ts were performed on various polystyrene/ethylbenzene solutions with p olymer concentrations ranging from 40% up to 100% and temperatures fro m T-g + 30 degrees C up to 70 degrees C (230 degrees C for polymer mel ts). The basis polymers are two commerical grade polystyrenes (BASF) w ith M(w) = 247 kg/mol and 374 kg/mol, respectively. To avoid solvent l oss due to evaporating during the measurements, a special sealing tech nique was used. A phenomenological model which describes quantitativel y the relaxation spectrum of concentrated polymer solutions from the f low regime up to the glass transition regime is developed. The relaxat ion data of the respective polymer melt and the glass transition tempe rature of the solution are the only input parameters needed. The tempe rature dependence is described by a universal, concentration invariant WLF-equation. The relaxation spectra are divided into two parts accou nting for the entanglement and the segmental relaxation modes, respect ively. The relaxation strength related to the flow and entanglement re gime scale with c(2.3), whereas the segmental relaxation strength does not alter with concentration. All relaxation times change with concen tration proportional to c(3.5). Flow curves can be calculated from the se relaxation spectra and thus, our results are useful for engineering applications.