# Transient Spin Labeling of Plastics with Chlorine Dioxide

## TL;DR

This paper explores using chlorine dioxide radicals to label plastics for tracking and analysis, offering a new method to study plastic waste.

## Contribution

The novel use of chlorine dioxide radicals for spin labeling plastics and measuring their diffusion in polymers.

## Key findings

- Chlorine dioxide radicals can be used to label plastics for detection via electron spin resonance.
- The technique reveals how the radicals' mobility is restricted by the polymer matrix even at room temperature.
- Time-series measurements enabled the determination of the diffusion coefficient of the radicals in the polymer.

## Abstract

Plastic waste, one of the most critical problems for
humankind,
poses severe threats to ecosystems, wildlife, and human health. Tracing,
quantifying, and identifying types of plastic waste are crucial to
understanding its environmental pathways and developing targeted strategies
for reduction, recycling, and remediation. To contribute to addressing
this global issue, we investigated the spin-labeling capabilities
of chlorine dioxide (ClO2) radicals introduced into poly­(ethylene
terephthalate) and utilized electron spin resonance spectroscopy for
detection. The technique is capable of identifying plastic species,
as the unpaired electron of the radical molecule is strongly sensitive
to its local environment through its coupling parameters. Temperature-dependent
measurements revealed that the molecules are immobilized at low temperatures
and exhibit well-resolved anisotropic and hyperfine spectra that are
quantitatively described by a model spin Hamiltonian. Even above the
melting point of water, certain degrees of freedom remain restricted
as a result of the polymer matrix. Furthermore, employing a time-series
measurement at room temperature enabled us to determine the diffusion
coefficient of the molecule in the polymer.