We report a simple method for shape-controlled synthesis of iron oxide spinels such as magnetite (Fe3O4) and maghemite (gamma-Fe2O3) nanostructures using a thermoresponsive polymer poly(vinyl methyl ether) (PVME) by the alkaline hydrolysis of iron salt at low temperature (20 degrees C). Microscopic analysis confirmed the formation of needle- and flower-shaped iron oxide nanostructures depending on reaction conditions. High-resolution transmission electron microscopic analysis of the needle- and flower-shaped nanostructures as well as their corresponding selected area electron diffraction patterns revealed that the formed nanostructures are crystalline in nature. X-ray diffraction study reveals the formation of well-crystalline pure Fe3O4 and gamma-Fe2O3 nanostructures under different reaction conditions. Fourier transform Infra-red spectroscopic analysis confirms the adsorption of PVME on the surface of iron oxide nanostructures. Finally, the magnetic properties of gamma-Fe2O3 and Fe3O4 nanostructures is studied that shows the superparamagnetic behavior of the formed iron oxide nanostructures. (C) 2014 Elsevier B.V. All rights reserved.