Seven linear amylose tris(n-octadecylcarbamate) (ATODC) samples ranging in the weight-average molar mass Mw from 2.4 x 10(4) to 1.5 x 10(6) g mol(-1) and their seven cyclic analogues (cATODC) of which Mw are from 3.6 x 10(4) to 1.9 x 10(5) g mol(-1) were prepared to characterize their conformation in tetrahydrohuran (THF), in 2-octanone (MHK), and in tert-butyl methyl ether (MTBE). Light and small-angle X-ray scattering and viscosity measurements in dilute solution were employed to determine the particle scattering function P(q), the z-average mean-square radius of gyration < S-2 > z, and the intrinsic viscosity [eta]. The obtained data were analyzed in terms of the wormlike chain model to determine the helix pitch per residue h and the Kuhn segment length lambda(-1) which is a measure of the chain stiffness and equal to twice the persistence length. The parameters indicate that the linear ATODC has an appreciably extended local helical structure and high chain stiffness while the latter parameter lambda(-1) in THF is lower than those for amylose alkylcarbamates with shorter side chains. This is most likely due to the repulsion between relatively long side groups. This chain extension and less stiff main chain were more significantly observed for the cyclic chains. Lyotropic liquid crystallinity in concentrated solutions supports the high rigidity of ATODC and cATODC chains in solution. (c) 2017 Elsevier Ltd. All rights reserved.