2-Vinyl-4,6-diamino-1,3,5-triazine (VDAT) polymers have demonstrated functionality of adsorbing water-soluble molecules via stable hydrogen bonding in aqueous environment. However, traditional methods for the polymer particle synthesis face challenges due to the poor solubility of VDAT. In this study, a semi-continuous precipitation polymerization was developed to synthesize VDAT polymer nanoparticles in aqueous phase. By continuously feeding VDAT to hot water in the presence of a cationic free radical initiator, the dissolved VDAT underwent precipitation polymerization and its concentration was kept below the saturation limit while the fragments of ionic initiator provided electrostatic repulsion for particle stabilization. VDAT feeding rate and the monomer to initiator ratio throughout the polymerization were the key factors to achieve good particle morphology and narrow size distribution. The synthesized nanoparticles quickly adsorbed bovine hemoglobin in water. The adsorption isotherm study and theoretical estimation suggested a monolayer adsorption. The adsorption efficiency varied significantly with both pH and ionic strength which were controlled to manipulate physiochemical characteristics of both the nanoparticles and the protein macromolecules. The adsorption results suggested an important role of hydrogen bonding and its interactions with electrostatic attraction/repulsion and hydrophobic affinity.