Surface-independent vertical orientation of cylindrical microdomains in block copolymer thin films directed by comb-coil architecture

Vertically oriented cylindrical microdomains of block copolymer thin films consisting of polystyrene and poly(methyl methacrylate) were fabricated regardless of the substrate by introduction of a grafted architecture into the diblock copolymer chains. A series of comb-coil block copolymers, poly(methyl methacrylate)-b-poly(2-(2-bromopropionyloxy)-ethyl acrylate)-g-polystyrene (PMMA-b-PBPEA-g-PS) with various lengths of PS were synthesized by combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP). When the volume fraction of PS was 75%, microphase separation produced cylindrical microdomains of PMMA surrounded by PS matrix in a thin film state after thermal annealing. Analysis of the thin films after subsequent etching of PMMA domains by atomic force microscopy, cross-sectional scanning electron microscope images and grazing incidence X-ray scattering measurements showed that the microdomains were oriented perpendicular to various substrates including metals, silicon, polymers, and even patterned surfaces. Steric repulsion between the grafted chains during the phase separation was attributed to the driving force for perpendicular orientation of the cylindrical microdomains without the aid of external fields.