An attempt was made to evaluate molecular parameters of poly(hexamethyleneadipamide) (nylon 6,6) in mixture of calcium chloride and methanol with various calcium chloride concentrations (weight fraction W-ca against weight of the solvent mixture) using light scattering method. Dissolved state of the polymer was discussed in connection with the chain conformation based on data of viscosity, adiabatic compressibility, infrared (IR) spectra and H-1 and C-13 NMR spectra. The second virial coefficient A(2), obtained by the light scattering method, remarkably decreases with a decrease of W-ca below 0.15 and is expected to become zero at W-ca of ca. 0.115 (i.e., Flory's Theta solvent). From values of conformation parameter and characteristic ratio of the polymer, evaluated from radius of gyration at the Theta state, the nylon 6,6 molecule is judged to be very flexible in the unperturbed state. The viscosity of the polymer solution showed specific W-ca dependence, around W-ca = 0.15. The results of the viscosity, adiabatic compressibility, IR and NMR measurements on the solvent mixtures revealed that the above W-ca = ca. 0.05, mole ratio of the undissociated CaCl2 monotonically increases with W-ca and methanol molecules strongly interact with calcium chloride probably forming organometallic complex. The results of H-1 and C-13 NMR and IR measurements on the polymer solutions suggested that dissolution of nylon 6,6 in calcium chloride-methanol mixture with W-ca greater than or equal to 0.1 is realized at least by interaction of methanol and chlorine parts in the complex with amide carbonyl and amine: In the range of 0.1 less than or equal to W-ca < 0. 15, selective absorption of weakly bound methanol molecules with the complex to nylon 6,6 plays an important role to determine the very compact chain conformation of the nylon 6,6 chain. Above W-ca = 0.15 dissolution of nylon 6,6 takes place by direct interaction of the very bulky and metastable associate form of solvent to polymer, which brings about large expansion of the nylon 6,6 chain in the solution.
