Concentrated solutions of cellulose and amylose were prepared with an ionic liquid 1‐butyl‐3‐methylimidazolium chloride (BmimCl), which was chosen as a good solvent for these polysaccharides. Dynamic viscoelasticity of the concentrated solutions was examined to obtain the molecular weight between entanglements, Me. The value of Me in the molten state (Me,melt), a material constant that reflecting the entanglement properties, was determined for cellulose and amylose by extrapolating Me to the “melt.” A marked difference in Me,melt was found: 3.2 × 103 for cellulose and 2.5 × 104 for amylose. The value of Me,melt for cellulose, which is composed of β‐(1,4) bonding of D‐glucose units, is very close to those for polysaccharides with a random‐coil conformation such as agarose and gellan in BmimCl. The much larger Me,melt for amylose can be attributed to the helical nature of the amylose chain, α‐(1,4)‐linked D‐glucose units. The effect of concentration on the zero‐shear viscosity for the solutions of cellulose and amylose was also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

The rheological properties of agarose solutions were examined under the effect of entanglement coupling between agarose chains. Agarose solutions were prepared by using an ionic liquid 1-butyl-3-methylimidazolium chloride as a solvent. The concentration of agarose was varied from 1.1 Â 10 1 -2.1 Â 10 2 kg m À3 . The master curves of the angular frequency (x) dependence of the storage modulus (G 0 ) and the loss modulus (G 00 ) showed a rubbery region in the middle x region and a flow region at low x region, respectively. The molecular weight between entanglements (M e ) for agarose was calculated from the plateau modulus. Moreover, M e for agarose melt was determined to be 2.3 Â 10 3 from the concentration dependence curve of M e . By using well-known empirical relations in polymer rheology, information on molecular characteristics of sample agarose was derived.

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The rheological behavior of galactomannans in concentrated solutions was examined by using dynamic viscoelasticity measurements. Concentrated solutions of three galactomannans, guar gum, tara gum, and locust bean gum were prepared with an ionic liquid 1-butyl-3-methylimidazolium chloride as the solvent. Each galactomannan solution showed angular frequency dependence curves of the storage modulus and the loss modulus which were characteristic of a solution of entangled polymer chains. The molecular weight between entanglements (Me) was obtained from the plateau modulus and the concentration dependence of Me showed Me in the molten state (Me,melt) to be 4.6×10(3), 3.2×10(3), and 2.7×10(3) for guar gum, tara gum, and locust bean gum, respectively. It was found that the material constant Me,melt depends on the mannose/galactose ratio of the galactomannans. The number of monosaccharide units between entanglements in the molten state for the galactomannans varied within the range found for other polysaccharides such as cellulose and agarose in ionic liquids, suggesting that all the galactomannans take a random-coil conformation in ionic liquid solutions.

INTRODUCTIONThe molecular structure of polysaccharides has led to the belief that these polymers are stiff. The characteristic ratio (C N ) for polysaccharides is rather high, although reported C N values are limited to typical polysaccharides such as cellulose 1 and gellan. 2 If we can prepare concentrated solutions of polysaccharides, we can determine the molecular weights between entanglements in the molten state (M e,melt ) for these polysaccharides, 3-5 which reflects the chain properties, that is, the flexibility of the chain. Since the first report that cellulose has good solubility in ionic liquids, 6 many studies have been conducted to determine the solution properties of polysaccharides at high concentrations. We prepared concentrated solutions of several kinds of polysaccharides in an ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) and carried out rheological measurements for the solutions to determine M e,melt for the polysaccharides. 7-9 The experiments yielded rather small values of M e,melt for the polysaccharides; for example, 8 M e,melt was 2.3Â10 3 for agarose, which is composed of (1,3)-b-D-galactopyranose and (1,4)-3,6-anhydro-a-L-galactopyranose. 10 This value appears to be much smaller than expected for a stiff polymer and is actually comparable to the M e,melt for the simplest flexible polymer polyethylene (M e,melt ¼1.3Â10 3 ), 3 although no reported value of C N for agarose is available. Why the M e,melt for polysaccharides is so small is not clear at present. The M e,melt for amylose was also determined and was much larger than that for cellulose. 7 To explain the M e,melt values, it is necessary to examine whether the use of an ionic liquid as a solvent affects the estimation of M e,melt . It has been proposed that ionic liquids form three-dimensional structures even in the liquid state because of cation-anion hydrogen bonding and cation-cation ring stacking. [11][12][13] The threedimensional structure may contribute to the modulus of the solutions; if the elasticity due to the network of solvent molecules contributes to the plateau modulus (G N 0 ), then M e,melt is reduced. The aim of this study is to clarify whether or not the network formed by the ionic liquid molecules contributes to G N 0 . Concentrated solutions of agarose were prepared by using formamide (FA), N-methylformamide (MFA) and BmimCl as solvents. Angular frequency (o) dependence curves of the storage and loss moduli (G¢ and G 00 , respectively) were compared among these solutions.