pH-Dependent Solution Micellar Structure of Amphoteric Polypeptoid Block Copolymers with Positionally Controlled Ionizable Sites

Published

August 14, 2023

Author(s)

Meng Zhang, Yun Liu, Xiaobing Zuo, Shuo Qian, Sai Pingali, Richard E. Gillilan, Qingqiu Huang, Donghui Zhang

Abstract

Solution self‐assembly of ionic block copolymers (BCP) with randomly distributed ionization sites along the hydrophilic segments have been extensively studied. By contrast, the roles of positionally controlled ionization sites along the BCP chains in their micellization and resulting micellar structure is still not understood. Herein, three amphoteric polypeptoid block copolymers with one fixed ionizable site and the other varied along the chain length, have been synthesized by sequential ring‐opening polymerization method. The micellization of the amphoteric polypeptoid BCP in dilute aqueous solution and the micellar structure at different solution pHs have been investigated by a combination of scattering and microscopic methods. Transmission-electron microscopy (TEM) and small-angle neutron scattering (SANS) and small‐angle X‐ray scattering (SAXS) analyses revealed that the amphoteric polypeptoid BCPs formed core-shell ellipsoidal micelles with varying levels of molecular ordering in the micellar core. The micellar structures (e.g., aggregation number, radius of gyration, and the chain packing order in the micellar core) were found to be dependent on the solution pH and the position of the ionizable site on the chain. In particular, the position of the ionizable sites modulates the solvation level and the chain conformation of individual polymers in the micelles, and consequently dictates the pH dependent behavior of the micellar structure. This study has demonstrated that controlling the ionization sites along the BCP polymer chain is an effective strategy to tailor the pH‐induced structural re‐organization of the BCP polymer chains in aqueous solution.

Citation

Biomacromolecules

Volume

24

Issue

8

Pub Type

Journals

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DOI Link

Keywords

block copolymer, polypeptoid, small angle neutron scattering, micelle, ionizable site

Citation

Zhang, M. , Liu, Y. , Zuo, X. , Qian, S. , Pingali, S. , Gillilan, R. , Huang, Q. and Zhang, D. (2023), pH-Dependent Solution Micellar Structure of Amphoteric Polypeptoid Block Copolymers with Positionally Controlled Ionizable Sites, Biomacromolecules, [online], https://dx.doi.org/10.1021/acs.biomac.3c00407 (Accessed April 27, 2024)