A new class of lipopolymers with polyoxazoline headgroups has been synthesized for the design of drug carriers, These amphiphatic molecules form stable monolayers at the air-water interface. Using X-ray and neutron reflectivity, the molecular conformations of the lipopolymer at the liquid surface were investigated as a function of surface pressure. The data are consistent with a fraction of the polyoxazoline moieties in brush-like conformations coexisting with a smaller fraction that is closely associated with the interface. Across the phase transition that is detected in the isotherm, the relative proportion between these two fractions is shifted. However, no qualitatively distinct molecular conformations are detected that would hint at a phase transition with respect to the polymer chains.