  The problem of estimating the size of the cooperatively rearranging regions
(CRRs) in supercooled polymeric melts from the analysis of the $\alpha$-process
in ordinary relaxation experiments is addressed. The system is treated with the
canonical formalism as an ensemble of CRRs, which are described by a stationary
distribution relative to the rearrangement energy threshold. The process
whereby a CRR changes its configuration is viewed as consisting of two distinct
steps: a reduced number of monomers reaches initially an activated state
allowing for some local rearrangement; then, the regression of the energy
fluctuation may take place through the configurational degrees of freedom, thus
allowing for further rearrangements on larger length-scales. The latter are
indeed those to which the well known Donth's scheme refers. Two main regimes
are envisaged, depending on wether the role played by the configurational
degrees of freedom in the regression of the energy fluctuation is significant
or not. It is argued that the latter case is related to the occurrence of an
arrhenian dependence of the central relaxation time. Data of the literature are
rediscussed within this new framework.
