To explore the relationship between thermal properties of a polymer and the biological performance of the resulting nanoparticle, all other parameters, including the hydrophobicity, should be kept constant. For this purpose, a gradient and a block copolyester were tailor-made via the triazabicyclodecene catalyzed ring-opening copolymerization of delta-valerolactone (delta VL) and delta-decalactone (delta DL) to match the hydrophobicity of poly(epsilon-caprolactone) (P epsilon CL). The degree of crystallinity of the semicrystalline materials was significantly reduced due to the incorporation of amorphous P delta DL segments, as confirmed by dynamic scanning calorimetry. Atomic force microscopy revealed short and randomly oriented crystals in the gradient copolymer but longer and parallel aligned crystals for the block copolymer and P epsilon CL. The stiffness of nanoparticles (D-h approximate to 170 nm) prepared from the polyesters correlated to the bulk crystallinity. The set of nanoparticles with constant hydrophobicity and size will facilitate direct access to the influence of the nanoparticle crystallinity on biological processes such as enzymatic degradation, drug release, and cellular uptake.