  Exact bounds are obtained for the quenched free energy of a polymer with
random hydrophobicities in the presence of an interface separating a polar from
a non polar solvent. The polymer may be ideal or have steric self-interactions.
The bounds allow to prove that a ``neutral'' random polymer is localized near
the interface at any temperature, whereas a ``non-neutral'' chain is shown to
undergo a delocalization transition at a finite temperature. These results are
valid for a quite general a priori probability distribution for both
independent and correlated hydrophobic charges. As a particular case we
consider random AB-copolymers and confirm recent numerical studies.
