Viscosity, molecular weight and concentration relationships at 298 K of low molecular weight cis-polyisoprene in a good solvent

A series of six well characterised homopolymers of cis-polyisoprene (PIP) ranging from 1180 to 115,000 molecular weight were utilised to explore viscosity and the scaling relationship between viscosity and concentration in dodecane (good solvent). For each polymer molecular weight, the relative viscosity of PIP in dodecane at 298 K was measured at several polymer concentrations using capillary viscometry. The linear extrapolation of experimental data based on Huggins, Kramer, Martin and Schulz-Blaschke equations was used to find the intrinsic viscosity at infinite dilution for each polymer molecular weight. The single-point method of evaluation of the intrinsic viscosity was also used for comparison. The Mark-Houwink fit of the data gave power index of 0.72 indicating that dodecane is good solvent for PIP and the latter exists in solution as open flexible coil. Both the radius of gyration and critical chain overlap concentration, c*, were derived from measured intrinsic viscosities. Plot of the relative viscosities versus the scaled concentration c/c*, resulted in single curve with slope value 4.44 × 10−2 and correlation coefficient r2 = 0.996, indicating good linear fit.