While the Flory–Fox equation describes many polymers very well, it is more reliable for large values of M  and samples of narrow weight distribution.  As a result, other equations have been proposed to provide better accuracy for certain polymers.  For example:
This minor modification of the Flory–Fox equation, proposed by Ogawa, replaces the inverse dependence on M  with the square of the product of the number-average molecular weight, M , and weight-average molecular weight, M .  Additionally, the equation:
was proposed by Fox and Loshaek, and has been applied to polystyrene, polymethylmethacrylate, and polyisobutylene, among others.
However, it is important to note that despite the dependence of T  on molecular weight that the Flory-Fox and related equations describe, molecular weight is not necessarily a practical design parameter for controlling T  because the range over which it can be changed without altering the physical properties of the polymer due to molecular weight change is small.