Methacrylate monomers were functionalized with a 4-hydroxythiazole chromophore and copolymerized with methyl methacrylate via RAFT. Nanoparticles of 120 and 500 nm in size were prepared without using stabilizers/surfactants. For comparative studies, preparative ultracentrifugation was applied for the separation into small and large particle fractions. All suspensions were characterized by DLS, AUC, and SEM and tested regarding their stability during centrifugation and re-suspension, autoclavation, and incubation in cell culture media. In vitro studies with mouse fibroblast cell line and differently sized NP showed a particle uptake into cells. Biocompatibility, non-toxicity, and hemocompatibility were demonstrated using a XTT assay, a live/dead staining, and an erythrocyte aggregation and hemolysis assay.