Cloud Point Curves of Aqueous Solutions of Poly(N-ethylmethacrylamide)
Aqueous solutions of poly( N -ethylmethacrylamide) have a lower critical solution temperature (LCST). Cloud point curves of five polydisperse samples ( M w . 10 -6 = 0.06 to 2.04) in aqueous solutions at concentrations from 0.002 to 0.1 g/ml were obtained. The threshold concentration was found to be almost independent of the molecular weight. The threshold temperature decreases moderately with increasing M and the limiting value for infinite M obtained by the Shultz-Flory method is Θ L PE = 340.5 K. This value is lower by 2.5 K than the temperature Θ L η at which the intrinsic viscosity is proportional to the square root of the molecular weight. The difference cannot be assigned to experimental errors. The entropy-of-dilution parameter is negative (ψ = -2) and much higher than the value obtained from dilute solution properties. The differences in Θ and ψ values are discussed in terms of theory of polymer solutions where a higher-order interaction parameter is included.