expansion factor in polymers

The ratio of a dimensional characteristic of a macromolecule in a given solvent at a given temperature to the same dimensional characteristic in the $θ$ state at the same temperature. The most frequently used expansion factors are: expansion factor of the mean-square end-to-end distance, $α r = < r 2 > < r 2 > 0$ ; expansion factor of the radius of gyration $α s = < s 2 > < s 2 > 0$ ; viscosity expansion factor $α η = ( η η θ ) 1 3$ where $η$ and $η θ$ are the intrinsic viscosity in a given solvent and in the $θ$ state at the same temperature, respectively. Expansion factors defined by different dimensional characteristics are not exactly equal, nor need they have a constant ratio as a function of relative molecular mass.

Source:

Purple Book, p. 59