Tuning the Properties of Poly(ethylene glycol) Films and Membranes by the Molecular Weight of the Precursors

We show that ultrathin poly(ethylene glycol) (PEG) films and freestanding membranes can be readily prepared by thermally activated cross-linking of amine/epoxy-decorated STAR-PEG compounds with the molecular weight (MW) varying from 2000 to 20,000 g/mol. The thickness of these objects, recorded in the 10–330 nm range, could be precisely controlled. They all exhibit characteristic hydrogel, biorepulsive, and elastic properties, with the exact parameters depending on the MW. This factor (MW) affects, in particular, the swelling behavior and biomolecule permeability of the PEG films as well as the elastic properties of the PEG membranes, which show an extreme elasticity with Young's moduli of 2.1–5.2 MPa at 100 nm thickness. Contrary to intuitive expectations, the Young's modulus does not decrease but increases with the increasing MW, which is explained by the progressive alignment of the PEG chains within the cross-linking network. The high stability, parameter tunability, and exceptional characteristics of the STAR-PEG-originated films and membranes make them promising candidates for application in biochemistry, medicine, and soft matter nanotechnology.