Polymer films comprising crosslinked random copolymers and methods for making the films are provided. Also provided are polymer films comprising random copolymers that are covalently linked to an underlying substrate. The polymer films can be incorporated into structures in which the films are employed as surface-modifying layers for domain-forming block copolymers and the structures can be used for pattern transfer applications via block copolymer lithography. The crosslinks between the random copolymer chains in the polymer films or the links between the random copolymer chains and the substrate surface are characterized in that they can be cleaved under relatively mild conditions.