Crystallization of Polymer Brushes with Poly(ethylene oxide) Side Chains

Surface-initiated atom transfer radical polymerization (ATRP) of methoxypoly(ethylene glycol) methacrylate (MPEGMA) macromonomers from immobilized initiators leads to thin films of comblike polymer brushes. The aqueous ATRP procedure results in essentially constant film growth rates and yields coatings with thicknesses as high as 400 nm. Polymers with side chains consisting of 22−23 ethylene oxide repeating units align to form crystalline materials analogous to their nonbrush analogues. However, polarized optical microscopy shows that the polymer films crystallize as two-dimensional spherulites. Both AFM images and reflectance FT-IR spectra of the films are consistent with crystalline lamellae preferentially oriented normal to the surface for brushes with thicknesses above 100 nm. As the film thickness decreases, the favored orientation shifts to crystalline lamellae parallel to the surface, with the PEO side chains oriented perpendicular to the surface. The lamellae orientations are related to polymer−surface interactions as well as to the “comblike” polymeric structure.