Ring-opening metathesis polymerization of norbornene derivatives is a powerful strategy to prepare materials for applications ranging from drug delivery to high-performance applications. A fundamental limitation of this approach, however, is the lack of backbone degradability of the resulting compounds. We describe a general strategy to prepare backbone-degradable copolymers derived from known and commercially available norbornene derivatives. With this approach, we can generate complex polymer architectures with rates of backbone degradation tunable over multiple orders of magnitude while maintaining the properties of the parent polynorbornene polymer. This approach is an enabling strategy to generally improve or modulate the property of known polynorbornenes in a straightforward fashion, opening the door to new classes of responsive materials.