Partly charged copolymers of diallyldimethylammonium chloride (DADMAC) and acrylamide couple easily to charged DPPA monolayers. For all pressures investigated, X-ray diffraction measurements at : grazing incidence show an oblique structure with much higher tilt angles than that of DPPA on pure water. Short positional correlation lengths are due to the entropic interactions within the flexible adsorption layer. There is no preferred direction of the coupling. The coupling of the charged polyelectrolyte PDADMAC to a partly charged monolayer consisting of a 1:1 mixture of DPPA and DPPE prevents the hexagonal packing with upright chains up to a lateral pressure of 40 mN/m. The oblique-rectangular transition is shifted to higher pressure compared to that for the system on water. The stiff polymer couples preferentially perpendicular to the direction of the chain tilt.