The Raman and IR spectra of lactic acid and sodium lactate in aqueous solution and methyl lactate as a pure liquid were recorded from 3600 to 100 cm-'. Vibrational assignments are proposed for the three compounds. The effects of hydrogen bonding on the 6 0 H vibrations of the hydroxyl alcohol group were studied and the results suggest both inter-and intra-molecular hydrogen-bonded association.

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The shear flow of cellulosic derivatives (methylcellulose and hydroxypropylmethylcellulose with different degrees of methoxyl and hydroxypropyl substituents) has been studied. The static light scattering and intrinsic viscosity measurements have allowed the determination of the weight-average molecular weight (M w), radius of gyration (R g), critical overlap concentration C*, intrinsic viscosity [η], and Huggins constant. These results indicate that the studied methylcellulose A4M and hydroxypropylmethylcellulose F4M have comparable molecular weight and an intrinsic viscosity of the same magnitude in pure water. However, hydroxypropylmethylcellulose K4M possesses a greater molecular weight and a corresponding high value of [η]. Even if hydroxypropylmethylcellulose F4M and K4M have different molecular weights and different [η], they show a rather similar C* value. Although the critical parameter is the same for A4M and F4M, the C r* concentration characterizing the end of the dilute regime is lower in the case of methylcellulose derivative, indicating that the absence of any hydroxypropyl substituent on the polymer chain is responsible for the A4M chains to develop associative interactions among themselves more favorably. This may be explained by their tendency to escape from the aqueous medium. Although the studied hydroxypropylmethylcellulose samples differ from their methoxyl degree of substitution and their hydroxypropyl molar substitution (F4M, DS = 1.76, MS = 0.14; K4M, DS = 1.39, MS = 0.21), their aqueous solutions display a rather similar rheological behavior in steady flow, suggesting that the distribution of the various substituents along the polymer chain does not induce a great difference on the interactions that lead to entangled structures of comparable density and cohesion.

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The rheological behavior of two hydrogels, poly(sodium acrylate) and polyacrylamide gels, synthesized in the presence of the same crosslinking agent molecule, N,N′‐methylene bis‐acrylamide, has been investigated. The variation of the norm of the complex shear modulus |G*| vs. the monomer concentration (sodium acrylate or acrylamide) exhibited a different power law, depending on the nature of the monomer molecule. This discrepancy was ascribed to the influence of the properties of the monomer molecules on the crosslinked structure of the gelified networks. The analysis of the experimental results have allowed the suggestion that the elasticity exponent value was dependent on the length and on the conformation of the polymer chains connecting the junctions points of the network. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2535–2541, 1997