  The evolution of the symmetry energy coefficient of the binding energy of hot
fragments with increasing excitation is explored in multifragmentation
processes following heavy-ion collisions below the Fermi energy. In this work,
high-resolution mass spectrometric data on isotopic distributions of
projectile-like fragments from collisions of 25 MeV/nucleon 86Kr and 64Ni beams
on heavy neutron-rich targets are systematically compared to calculations
involving the Statistical Multifragmentation Model. The study reveals a gradual
decrease of the symmetry energy coefficient from 25 MeV at the compound nucleus
regime (E*/A < 2 MeV) towards 15 MeV in the bulk multifragmentation regime
(E*/A > 4 MeV). The ensuing isotopic distributions of the hot fragments are
found to be very wide and extend towards the neutron drip-line. These findings
may have important implications to the composition and evolution of hot
astrophysical environments, such as core-collapse supernova.
