It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A2 = 0) Recently

in studies of the temperature dependence ofthe chain conformation in solution

we found that the change of the chain conformation clearly underwentthree different stages which could be viewed as the "gas". "liquid" and "solid" states in terms of the freedomof the "blobs" on the chain. The transition temperature between the first and second stages corresponds nicely to the Θ-temperature determined by the conventional method.It reveals

for the first time

that the Θ-temperature can be deduced from the conformation change of a single polymer chain in solution

which is important not only in conception

but also in practice.