Extremely straight and laterally aligned cylindrical microdomains of block copolymer (BCP) films have been prepared by simply covering the BCP films with a top coat and dewetting the latter via thermal annealing to generate shear flow in the BCP underlayer. The polystyrene-block-polydimethylsiloxane microdomains are perfectly aligned with sunburst direction along the polyvinyl alcohol top-coat dewetting front from the nucleation point to the end of the dewetting front. This alignment is at least 150 mu m long and the aspect ratio is higher than 15 000: 1. Studying the morphologies obtained as a function of top-coat and BCP film thickness at various annealing temperatures, highly ordered BCP patterns are obtained for a wide range of shear rates, while higher (but not the highest) temperatures and thicker BCP films lead to more ordered microdomain patterns, because of increased polymer mobility and a reduced surface/interface effect. An imprinting process is also introduced to pattern top coats, which then provide selective control of the dewetting direction so that unidirectionally aligned BCP patterns can be created in specific areas.