We have investigated the linear viscoelastic behavior of guar gum solutions as a function
of frequency, temperature, polymer concentration, and molecular weight. This was done to sort out the
importance of different relaxation mechanisms like reptation or the breakup of physical bonds. In the
kilohertz regime, Rouse behavior is observed. At lower frequencies, two storage modulus plateau zones
were found, indicating two additional relaxations. One is operative between 1 and 100 Hz and gives rise
to a very broad relaxation spectrum, even for monodisperse guar. Describing the dependencies of the
relaxation time and low-shear viscosity on concentration and molecular weight with power laws resulted
in unusually high coefficients. The second relaxation becomes manifest below 0.01 Hz and has not been
earlier reported. Here the temperature dependence is very strong whereas all other dependencies are
weak. Analyzing the experiments with existing models for transient polymer networks revealed that at
best a partial decription of the experimental dependencies can be obtained. It was concluded that at
least two different relaxation mechanisms must play a role, classical reptation not being one of these.
Best overall predictions were obtained with a model assuming two types of associations. However, also
the picture of star polymer-like structures held together via bonds with a long lifetime could give
comparable predictions. For a further distinction between these mechanisms, more information about
the mesoscopic structure is needed.