Lipopolymers are lipids with a polymer chain covalently attached to the lipid. We studied the infrared reflection absorption behavior as a function of molecular area of Langmuir monolayers of an ether lipopolymer, DC(18)Gly-M-35 (35 monomer units). A plateau region was observed in the monolayer isotherm. Within this region the CH2 asymmetric and symmetric stretching mode absorptions shifted toward lower absorption frequencies (6 and 4 cm(-1), respectively). This indicates that the plateau is accompanied by strong local ordering in the lipopolymer, which contradicts previous suggestions that the plateau correlates with a mushroom-brush transition in the polymer.