The phase behaviour in thin films of an asymmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymer with a molecular weight of 39 kg mol− 1 was assessed at a wide range of temperatures and times. Cylindrical PMMA structures featuring a diameter close to 10 nm and perpendicularly oriented with respect to the substrate were obtained at 180 C in relatively short annealing times (t≤ 30 min) by means of a simple thermal treatment performed in a standard rapid thermal processing machine.