Analysis of Steric Hindrance Effect on the Core Formation of Brush-Arm Star Polymer Nanogels During Ring Opening Metathesis Polymerization

Document Type

Article

Publication Date

6-12-2025

Abstract

We present a method that makes structural changes to the core of Brush-Arm Star Polymer (BASP) nanoparticles to possess more hydrogel-like characteristics by analyzing the effect of steric hindrance on core formation, producing “BASP nanogels”. Size exclusion chromatography (SEC), Dynamic light scattering (DLS), and Electron paramagnetic resonance spectroscopy (EPR) analyses reveal that cross-linking and core formation are affected by the steric hindrance of polyethylene glycol macromonomers (PEG-MMs) during ring opening metathesis polymerization (ROMP) of nitroxide-conjugated BASPs. The size and molecular weight of BASP nanogels depend on the ratio of acetal cross-linker (N) to macromonomer (X): N:X. Generally, the hydrodynamic diameter and molecular weight significantly increase with a larger N:X ratio due to the increased accessibility of cross-linking sites. EPR studies show that the BASP nanogel with N:X of 30:5 ratio strikes the right balance between effective cross-linking and increasing the size of the bottlebrush polymers. Other N:X ratios present a challenge for homogeneous core formation, and future studies will help increase understanding about the role of steric hindrance in core formation.

Comments

Originally published in Macromolecular Chemistry and Physics

Publication Title

Macromolecular Chemistry and Physics

DOI

https://doi.org/10.1002/macp.202500194

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