In this paper, a new and simple pathway to fabricate polymer brush layers with lateral control over the chemical composition is described. The process combines two subsequent free radical grafting from steps: in the first step, a micropatterned polymer brush is grown by photochemical initiation of the polymer growth from the surface through a mask in direct contact. The uncoated areas are then backfilled with a second polymer brush by using the unreacted surface-bound initiator molecules to thermally trigger a second polymerization. As an example for the overall process, the co-assembly of a micropatterned, soft, water-swellable layer consisting of the two-brush system poly(methacrylic acid) (PMAA)-poly(hydroxyethyl methacrylate) (PHEMA) is demonstrated.