Membranes based on functional hi compatible polymers can he regarded as a useful model system to study biological interactions. e.g. antibody antigen interactions or protein polymer interactions. These model systems may give a better insight into these processes and may help to find suitable polymeric structures offering, biocompatibility as well as reduced polymer protein interaction. In this respect, Langmuir-Blodgett (LB) layer formation at the air; water (A/W) interface is studied in respect to polymer architecture in this article. For this purpose, narrowly distributed N-(2-hydroxypropyl)-methacrylamide (HPMA) random and block copolymers have been prepared by the RAFT polymerization method. For random copolymers different molecular weights were prepared. As for the block copolymers also the ratio of hydrophilic and hydrophobic units was varied in order to study the influence of hydrophobic block length on collapse pressure and area. The molecular weights of all polymers were around 15k Da and 30 kat. In the case of block copolymers we found a direct correlation of the length of the hydrophobic block to the collapse area. Furthermore, hysteresis experiments clearly point out that block copolymers form stable LB layers. No remarkable changes in collapse pressure or area could be observed. In contrast the area occupied by random copolymers changes at each hysteresis cycle indicating a loss of polymer to the aqueous subphase. In addition the LB layers were transferred onto mica substrates. The block copolymers formed stable and defect free membranes over an area of 100 mu m(2) with a roughness (rms) 1.3-1,4 angstrom. On the contrary, membranes based on random copolymers turned out to have it higher surface roughness. Our findings clearly underline the influence of polymer structure on the LB layer formation at the A/W interface.