Conformational behavior of nylon 6 in mixed solvents

The intrinsic viscosity [eta], Huggins constant (K-H), laser light scattering, UV and IR measurements of Nylon 6 are made in m-cresol and its mixture with 1,4-dioxane at 20-60 degreesC. The intrinsic viscosity, R-g, A(2), (<S>(2))(1/2) (calculated from viscosity data), R-H, and UV absorbance initially increase and then decrease with the rise in 1,4-dioxane contents. The K-H and the transmittance of -OH group in IR spectra show an opposite trend to that of [eta]. The dielectric constant calculated from the refractive index of the solvent (m-cresol with 1,4-dioxane) and polymer solution shows a continuous decrease with the amount of 1,4-dioxane. Activation energy shows a minimum while linear expansion coefficient (alpha (3)) maximum with the addition of 1,4-dioxane. Change in [eta], K-H, and other characteristics of the polymer solutions with alterations in solvent composition and temperature are the result of variation in the thermodynamic quality of the solvent, its selective adsorption, hydrogen bonding, and conformational transitions. It has been concluded that the addition of 1,4-dioxane first enhances the quality of the solvent, encourages hydrogen bonding, and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. (C) 2005 Wiley Periodicals, Inc.