© 2015, Pleiades Publishing, Ltd. Molecular brushes having a polyimide (PI) backbone with degree of polycondensation n = 33 and polymethylmethacrylate (PMMA) side chains with two different degrees of polymerization (m = 63 and m = 114) were synthesized by the method of controlled atom transfer radical polymerization. Hydrophobic magnetite nanoparticles of a size of 18 ± 2 nm were prepared. Langmuir monolayers on the basis of the polyimide brushes and composite monolayers, containing magnetite nanoparticles with a hydrophobic surface, were formed at the water/air interface. It is found that, in the condensed state of the monolayer at the surface pressure values from 25 to 40 mN/m, the limiting surface area A0 per side chain of a brush grows with an increase in the length of PMMA side chains of polymer brushes almost by a factor of 2: from A0 = 744 ± 64 Å2 for PI-graft-PMMA-63 to A0 = 1644 ± 50 Å2 for PI-graft-PMMA-114. Increasing the magnetite solution ali
