# Gamma Irradiation-Induced Changes in Microstructure of Cyclic Olefin Copolymer (COC) Revealed by NMR and SAXS Characterization

## TL;DR

This study examines how gamma radiation affects the microstructure of a type of polymer used in medical packaging, revealing changes in particle size and spacing.

## Contribution

The novel contribution is the detailed characterization of gamma irradiation effects on COC microstructure using NMR and SAXS.

## Key findings

- COC with 35 mol% norbornene showed a 9.2% decrease in internal particle size and increased particle spacing after irradiation.
- COC with 57 mol% norbornene exhibited a 17.9% increase in internal particle size and decreased particle spacing after irradiation.

## Abstract

Cyclic Olefin Copolymer (COC) is an amorphous thermoplastic polymer synthesized through the catalytic copolymerization of α-olefin and cyclic olefin. When used in pre-filled syringes and pharmaceutical packaging, COCs require radiation sterilization. The radiation sterilization alters the microstructure of COC, which ultimately affects its performance and biosafety. In this study, to investigate the effects of γ-radiation on COC microstructures, ethylene-norbornene copolymers with various compositions, representative of COC, are studied by nuclear magnetic resonance (NMR) and small angle X-ray scattering (SAXS) techniques. During irradiation, the COC containing 35 mol% norbornene produced free radicals that triggered migration and reaction processes, leading to the formation of entanglements within flexible chain segments. This, in turn, affected nearby ring structures with high steric hindrance, resulting in a 9.2% decrease in internal particle size and an increase in particle spacing. Conversely, when the norbornene content in COC was increased to 57 mol%, the internal particle size increased by 17.9%, while the particle spacing decreased.