  We present a study of the physical properties of the vibrational excitation
in $\alpha$--helicoidal macromolecular chains, caused by the interaction with
acoustical and optical phonon modes. The influence of the temperature and the
basic system parameters on the vibron dressing has been analyzed by employing
the simple mean--field approach based on the variational extension of the
Lang--Firsov unitary transformation. Applied approach predicts a region in
system parameter space where one takes place an abrupt transition from
partially dressed (light and mobile) to fully dressed (immobile) vibron states.
We found that the boundary of this region depends on system temperature and
type of bond among structural elements in the macromolecular chain.
