Electrostatic interactions are well known to play a key role in the structure-function relationship of many naturally occurring biomacromolecules (polysaccharides, intrinsically disordered proteins, etc.); however, there is a significant lack in understanding on how to exploit this phenomenon in synthetic systems. In this study, a series of micelle-forming sequence-defined amphiphilic ionic block copolypeptoids were used, in tandem with solution pH, to garner control over the structural reorganization of well-defined aggregates in dilute aqueous solution. Charge patterning (i.e. number and position of ionic monomers along a chain) was achieved through implementation of the solid-phase submonomer method where one ionic monomer was precisely placed at different locations along the hydrophilic block of the copolymer. The weak acid functionality of the ionic group made the system sensitive to changes in its local environment (i.e. pH, ionic strength, etc.). Dynamic light scattering (DLS) and small angle neutron scattering (SANS) results revealed that as solution pH increased, micelles experienced a decrease in overall size (radius of gyration, Rg, and hydrodynamic radius, Rh) and aggregation number (Nagg), independent of ionic monomer position. Modulating ionic monomer position resulted in varying magnitudes of net decrease in micellar size as a function of increasing pH. Positioning the ionic monomer at the corona exterior resulted in a smaller net decrease in micellar size when compared to those micelles formed from chains where the ionic monomer was repositioned in the coronal interior. The stimulus response behavior was attributed to the delicate interplay between electrostatic interactions (when the ionic monomer was &lt;50% ionized) and the interfacial tension driving self-assembly (when the ionic monomer was &gt;50% ionized). This study highlights the potential for controlling nanoscale structures by wielding both polymer design and solution environment conditions.

Effects of charge patterning and solution pH on the micellar aggregation of amphiphilic ionic block copolypeptoids in dilute aqueous solutions

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ACS Fall 2022

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