Methylolcellulose triacetate macromolecules with degree of substitution by methylol groups of 4·5 and molecular weight M ranging from 1·8 × 104 to 9·4 × 105 were investigated by flow birefringence in dimethylformamide. Using the molecular weight dependence of the shear coefficient Δn/Δτ and the theory of flow birefringence of wormlike chains, the Kuhn segment length was found to be A = (400 ± 50) × 10-8 cm and the monomer optical anisotropy Δa = (3·3 ± 0·3) × 10-25 cm3. The magnitude of flow birefringence and viscometric characteristics of polymer solutions were measured between 7 and 50°C. The observed lowering of Δn/Δτ has been attributed to a decrease in equilibrium stiffness of polymer chains, due to a rupture of hydrogen bonds at elevated temperatures. © 1990.