Microphase Separation of Poly(2-(Dimethylamino)Ethyl Methacrylate)-b-Poly(Tetrahydropyranyl Methacrylate) Diblock Copolymer Thin Films.

Abstract

The microphase separation in diblock copolymer films comprising two chemically similar methacrylate blocks, poly(2-(dimethylamino)ethyl methacrylate) and poly(tetrahydropyranyl methacrylate), is investigated. Four symmetric diblock copolymers, with M_n's ranging from 4300 to 109 700 g mol^-1 and narrow molecular weight distributions, are synthesized by group-transfer polymerization, are spin-coated from ethyl lactate solutions and are subsequently solvent vapor annealed. The two lower M_n copolymers dewet the silicon substrates after annealing, whereas the two higher M_n copolymers reveal the formation of holes and islands by optical microscopy, suggesting their microphase separation into lamellae structures orientated parallel to the substrate. The ordering of these weakly segregated diblock copolymers is verified by X-ray reflectivity (XRR) and grazing-incidence small-angle X-ray scattering (GISAXS). XRR provided the film thickness and lamellae spacing by probing along the direction perpendicular to the sample surface, whereas GISAXS probes the nanoscale morphology along the sample plane and the lateral and vertical correlation lengths of the films by analyzing the diffuse scattering. The lamellae thicknesses determined by XRR and GISAXS are in good agreement with those measured by atomic force microscopy. The results hold great promise for the development of highly functional ordered nanostructures in thin film geometries for applications in energy, catalysis, and others.