Single-chain folding via intramolecular noncovalent interaction is regarded as a facile mimicry of biomacromolecules. Single-chain folding and intramolecular crosslinking is also an effective method to prepare polymer nanoparticles. In this study, poly(methyl methacrylate-co-2-ureido-5-deazapterines functionalized ethylene methacrylate) (P(MMA-co-EMA-DeAP)) is synthesized via free radical polymerization. The single-chain folding of P(MMA-co-EMA-DeAP) and the formation of the nanoparticles in diluted solution (concentration <0.005 mg/mL) are achieved via supramolecular interaction and intramolecular collapsing during the disruption-reformation process of the hydrogen bonding triggered by water. The size and the morphology of the nanoparticles are characterized by dynamic light scattering, transmission electron microscope, and atomic force microscope. The results show that the size of the nanoparticles depends on the molecular weight of the polymer and the loading of 2-ureido-5-deazapterines functionalized ethylene methacrylate (EMA-DeAP) on the polymer backbone. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1832-1840