Rheological Properties of 1,4-Polyisoprene over a Large Molecular Weight Range

The dynamic viscoelastic properties of anionically polymerized model 1,4-polyisoprene (PI) with 6−8% 3,4 microstructure and in the range of molecular weights between 1.5 × 103 and 3.2 × 106 g/mol were reanalyzed using linear rheology. Viscosities obtained in the zero shear-rate limit, η0, up to sufficiently high molecular weight PI samples indicated a clear transition to the pure reptation regime. All characteristic molecular weights, dividing the [η0,M]-interval in three different regimes could be obtained in high accuracy and a new “triangle” is proposed. The experimental data were analyzed in terms of the empirical Winter-relaxation BSW-model description for both dynamic moduli. The BSW parameters are determined and interpreted in terms of the packing model where possible. Limitations of the packing model are detected and discussed. Additionally, the parameters of the assumed distribution of relaxation times are compared to predictions of microscopic dynamic theories and useful correlations made. The publication deals, in part, with a misconception in the literature for estimates of the constraint release contribution. The monomeric friction coefficient ζ0, determined in this study for the first time rheologically for anionic PI itself agrees with the natural rubber analogue.