Footwear, carpet, soft furnishings, automotive interiors, and multi-layer packaging are examples of products manufactured from several types of polymers whose inextricability poses significant challenges for recycling at end-of-life. Here, we show that chemical circularity in mixed-polymer recycling becomes possible by controlling the rates of depolymerization of polydiketoenamines (PDKs) over several orders of magnitude through molecular engineering. Stepwise deconstruction of mixed-PDK composites, laminates, and assemblies is chemospecific, allowing a prescribed subset of monomers, fillers, and additives to be recovered in pristine condition at each stage of the recycling process. We provide a theoretical framework to understand PDK depolymerization via acid-catalyzed hydrolysis and experimentally validate trends predicted for the rate-limiting step. The control achieved by PDKs in managing thermal and materials entropy points to new opportunities for pairing circular design with sustainable manufacturing.