( Author: Thomas Wam...)Polymer Degradation Mechanisms Encountered in Pyrolysis-GC/MS

Author:
Thomas Wampler

CDS Analytical, Inc.
465 Limestone Road
Oxford, PA 19363-0277

Introduction

The use of analytical pyrolysis¹ with gas chromatography/ mass spectrometry (GC/MS) to study the structure of polymeric material must be based on an understanding of how these large molecules behave at elevated temperatures. The utility of the technique is based on the application of thermal energy to produce volatile fragments and products from a macromolecule compounds capable of being analyzed using GC/MS. The production of these analytes must, of course, be reproducible and follow chemical principles which permit the interpretation of results applied to unknown polymers.

Whether the sample represents evidence in a forensic lab, quality-control materials in the paint, adhesives, rubber or polymer industries or an unknown material for product comparison, the original polymeric structure is revealed in the compounds present in the chromatogram. The presence or absence of specific peaks in the pyrogram not only differentiates one sample from another, but may be crucial in identifying defects related to product performance. Understanding how these peaks are produced from the polymer is important in weighing the significance of the data and essential in identifying unknown materials, whether it is contamination in industrial processes, competitors products or evidence from a crime scene.

In general, the degradation mechanisms experienced by polymers are free-radical processes initiated by bond dissociation at the pyrolysis temperature. The specific pathway followed by a particular polymer is related to the relative strength of the polymer bonds and the structure of the polymer chain. These mechanisms are generally grouped into three categories: random scission, unzipping and side-group elimination.
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