Guar gum (GG) has been partially methyl-etherified under heterogeneous reaction conditions. The resulting products, (methyl ether guar: MG) with different degrees of substitution, have been characterized by means of viscosity, H-1 NMR, and FFIR measurements. The introduction of methoxyl groups along the polysaccharidic chains reduces the hydrogen bonding sites on the guar backbone reducing primarely the extent of hydrogen bonding between guar macromolecules, hence their aggregation tendency. A comparative analysis of Mark-Houwink-Sakurada parameters and of the characteristic ratio (C-infinity) of GG and MG samples in aqueous solution has been carried out using the Burchard-StockmayerFixman method for flexible and serniflexible chains. The MG chains exhibit more flexibility than those of native guar gum which is traceable to a disruption of intrachain hydrogen bonds. (c) 2005 Elsevier Ltd. All rights reserved.