We first synthesized a series of polymers (denoted as PPCx, where x represents the number-average degree of polymerization of PCL on each side) by grafting biodegradable polycaprolactone (PCL) from a hydroxyl-bearing PPcy initiator (P0) via ring-opening polymerization (Scheme S1). The resulting polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy (Figure ), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) (Figure & S4). As the number-average degree of polymerization (x) increased from 5 to 20, the melting temperature (Tm) of PPC polymers gradually rose from 30.5 to 44.3 o C. Tm remained nearly constant at 54.8 o C in the PPC25-179, which was close to that of blank PCL37 (51.8 o C) without PPcy units (Figure ). Colloidal nanoparticles (NPs) composed of these PPCx (1 mg/mL) were prepared in aqueous media by the typical nanoprecipitation method using PCL37-b-POEGMA60 as a surfactant. The average diameter of these NPs is approximately 45~65 nm, as measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM) (Figure ).