A high molar mass cotton linters cellulose was investigated by static and dynamic light scattering in semidilute solutions of the cadmium complexing Cd-tren (tren = tris(2-aminoethyl)amine). In this solvent cellulose has a Kuhn segment length of 15.3 nm and represents a semiflexible chain. Apparent molar masses M-app(c) and apparent radii of gyration R-g,R-app(c) were measured by light scattering. The influence of interchain interactions could be split off using either the theoretically well-known interaction among flexible chains or thin rigid rods, respectively. Estimations of the true molar mass M-w(c) and true radius of gyration R-g(c) at finite concentration c were obtained. Both molecular parameters increased with concentration when the overlap concentration was exceeded by a factor 4. Simultaneously, a slow mode of motion appeared in dynamic light scattering. The observations were interpreted as a result of association. The thermodynamic interaction could also be separated from the mutual diffusion coefficients and yielded the self-diffusion coefficients. A hydrodynamic radius R-h(c) was defined by applying the Stokes-Einstein relationship to the self-diffusion coefficient. This radius is interpreted as a correlation length for the influence of hydrodynamic friction. The zero shear viscosity showed behavior common to other linear chain molecules in solution. Shear thinning occurred in the semidilute regime. The curves could be fitted by the Cross approximation. A scaled master curve was obtained. The relaxation times for disengagement tau (d) increased with a power of 3.6 as the concentration was increased. This exponent is larger than 2.0 as predicted from the reptation model. The reversibly associating bonds cause a significant disengagement retardation of entangled chains.