Ionic block copolymers (BCPs) comprised an ionizable hydrophilic segment and a non-ionizable hydrophobic segment can self-assemble into core-shell type structures with varying geometries (e.g., spheres, cylinders, bicontinuous structures, lamellas, etc.) in selective solvents. The micellar structures can be influenced by many factors including electrostatic repulsion and counter-ion condensation. Polypeptoids are structural mimics of polypeptides with N-substituted glycine backbone and have been attracted lots of interests due to the broad applications (e.g., drug delivery carrier, theragnostic agent, tissue engineering matrices, etc.). We have previously synthesized a series of amphoteric polypeptoid BCPs with a fixed ionizable monomer at the hydrophobic segment and another ionizable monomer positioned either at the hydrophilic segment terminus or at the hydrophilic-and-hydrophobic segment junction and can form a core-shell ellipsoidal structure in aqueous solutions and also exhibited that the electrostatic interaction encoded in the polymer block sequence have a dominant effect on solution micellar structures. Due to the variable ionization state at hydrophobic segment, it is challenging to unambiguously determine the contribution of positionally varied charged monomer on the solution micellar structure. By end-capping the hydrophobic segment, we would be able to investigate the charge pattern effect on single-charged series to avoid any ambiguity and further study the end-capping effect on the micellar structures. Combination of small-angle scattering (SANS&SAXS) and transmission electron microscopic analyses revealed that the micelles formed a ellipsoidal structure below pK_a and formed board-like structure above pK_a. Move the ionizable monomer from the hydrophilic segment terminus to the hydrophilic-and-hydrophobic segment junction, the micelles have a tendency to form ellipsoid structure. The aggregate structure (radius of gyration and aggregation number) could be obtained by the modified Guinier analysis from SANS. The ionizable monomer position and end-group structure exhibited a significant effect on the solution micellar structure.

Donghui Zhang

Appearances