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The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [η] and Huggins constant (KH) of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10–60°C. The intrinsic viscosity, RH, Rg, A2, and (< S >2)1/2 (calculated from viscosity data) and "a" values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of [η]. The intrinsic viscosity, RH, Rg, A2, and (< S >2)1/2 have maximum values around 30–40°C in sulphuric acid/water system, whereas in m-cresol they fall at about 20°C. It has been concluded that the variation in size, interaction parameter (second virial coefficient), [η] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures. [ABSTRACT FROM AUTHOR]

The intrinsic viscosity [η], Huggins constant (KH), [η]0, α3 and flow activation energy values of nylon 6 have been measured in water/m-cresol (0/100–20/80) systems at different temperatures (20–60°C). It has been found that the intrinsic viscosity, [η]0 and α3 increase with the increase in water contents in m-cresol up to 15% and then decrease. They increase with the increase in temperature irrespective of solvent composition. It has been noted that the percent increase of α3 is the highest at 60°C and the lowest at 20°C for a particular solvent system. The intrinsic viscosity data obey Arrhenius equation over the considered conditions. The activation energy and the KH values decrease very sharply with the addition of water, giving a minimum value at 15% of water and then increase slowly. The variation of all the parameters has been explained in terms of variation in thermodynamic quality of solvent with the addition of water to m-cresol and change in temperature, resulting in the change of conformational and orientational properties of polymer molecules. This change of solvent quality also results in variation of selective sorption of solvent over the polymer, such as hydrogen bonding, etc. [ABSTRACT FROM AUTHOR]