Block Copolymers Composed of PEtOx and Polyesteramides Based on Glycolic Acid, <scp>l</scp>-Valine, and <scp>l</scp>-Isoleucine

Hydroxyl-functionalized poly(2-ethyl-2-oxazoline) (PEtOx) was utilized as a macroinitiator in a 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyzed ring-opening polymerization of morpholine-2,5-diones derived from l-valine and l-isoleucine. The degree of polymerization (DP) of the obtained polyesteramide (PEA) block copolymers was adjusted by the monomer to initiator ratio (DPPEtOx = 20; 15 ≤ DPPEA ≤ 85; 1.15 ≤ D̵ ≤ 1.37). In agreement with atomistic simulations, differential scanning calorimetry and wide-angle X-ray scattering indicated bulk miscibility of the individual block segments, in particular because of the loss of crystallinity. The solvatization of the hydrophilic PEtOx block in aqueous media induced phase segregation from the hydrophobic PEA blocks, as observed by cryo-transmission electron microscopy. This indicated a potential suitability for the delivery of hydrophobic pharmaceutical actives, while benefitting from a PEtOx shell exhibiting a stealth effect.