Polymeric nanoparticles were prepared through the chain collapse of linear polymers driven by the formation of dynamic covalent bonds. Linear chains of poly(vinylbenzaldehyde) were intramolecularly cross-linked through the formation of dynamic covalent acylhydrazone bonds with a bis-hydrazide cross-linker. The cross-linking density was shown to be controlled by the amount of crosslinker used. The resulting single polymer chain nanoparticles were then adorned through reaction of their remaining aldehyde units with a series of monoacyl hydrazides or alkoxyamines. Alternatively, the linear polymer chains could be fully adorned by reaction of their aldehyde units with the monoacyl hydrazides and then intramolecularly cross-linked through exchange reactions with the bis-hydrazide cross-linker. Both approaches proved effective routes to prepare single-chain polymer nanoparticles possessing high functional density.