Work

Cyclic Macromolecular Chains Visualized by Cryo-EM and AFM Reveal a Ring Expansion Polymerization Mechanism in a Classical Synthetic Pathway to Polyphosphazenes

Year: 2025

Type: article

Abstract: We observed individual macromolecular chains with distinct ring topology when studying cryogenic electron microscopy (Cryo-EM) images of a high molar mass polyorganophosphazene in its vitrified aqueous solution. The presence of monocyclic chains was confirmed by visualizing samples of the same macromolecule in its absorbed form by using atomic force microscopy (AFM). The polymer, poly[di(carboxylatophenoxy)phosphazene], PCPP, is synthesized via a two-stage process, which includes a ring-opening polymerization (ROP) and a subsequent macromolecular substitution transformation. The visualization of macrocycles, which are 20-60 nm in diameter, provides direct proof of a ring extension polymerization (REP) mechanism occurring in the chain-growth process commonly employed for the synthesis of high molar mass polyphosphazenes. Asymmetric flow field flow fractionation (AF4) analysis shows the presence of a faster moving fraction, which can be potentially attributed to macrocycles.

Source: ACS Macro Letters

DOI: 10.1021/acsmacrolett.5c00529

Authors: Raman Hlushko, Vivek M. Prabhu, Alexander K. Andrianov

Institutions: Institute for Bioscience and Biotechnology Research, University of Maryland, College Park, National Institute of Standards and Technology, Material Measurement Laboratory

Language: English

Topic: Advanced Polymer Synthesis and Characterization

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,500

Funders: National Institute of Standards and Technology, National Institute of Allergy and Infectious Diseases