Combining CROP and ATRP to synthesize pH-responsive poly(2-ethyl-2-oxazoline-b-4-vinylpyridine) block copolymers

Abstract

Herein, we present the synthesis and characterization of block copolymers based on poly(2-ethyl-2-oxazoline), a biocompatible and stealth polymer that has drawn considerable attention in biomedical-related applications, and poly(4-vinylpyridine), a polydentate ligand and pH-responsive polymer, with interesting characteristics for application as optical, magnetic, electronic, catalytic and conductive materials, as well as in the biomedical field. Poly(2-ethyl-2-oxazoline-b-4-vinylpyridine) block copolymers were synthesized by the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) followed by atom transfer radical polymerization (ATRP) of 4-vinylpyridine (4VP). P(EtOx-b-4VP) polymers with 4VP molar fractions ranging from 0.40 to 0.71 were obtained. These polymers presented a narrow molar mass dispersity (≈1.2) and molar mass in the range of 6.4–10.5 kDa. The thermal properties of P(EtOx-b-4VP) were evaluated by differential scanning calorimetry (DSC) and their implication in the self-assembly in solution is discussed. The critical micellar concentration in water was determined by fluorescence spectroscopy and the self-assembly of P(EtOx-b-4VP) in water/DMF and basic aqueous solutions was studied by turbidimetry and dynamic light scattering (DLS). The morphology of the resulting structures was assessed by cryogenic transmission electron microscopy (cryo-TEM). Depending on the composition of polymer and solution, different structures, namely micelles, vesicles and worm-like micelles, can be formed. Concerning the interesting properties of PEtOx (stealth behavior and biocompatibility), as well as P4VP (pH-responsive polydentate ligand), these materials show potential for application in drug delivery, diagnostic imaging and as templates for inorganic materials.