AbstractMeasured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase withTfor solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] withTwas observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata‐Stockmayer‐Roig, Fixman, and Stockmayer (Padé). These yielded values of −3.4 × 10−3to −4.7 × 10−3deg−1and −0.9 × 10−3to −2.4 × 10−3deg−1for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ‐temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critic