Structural Characterization of Ethylene-Propylene-Diene Rubbers by High-Resolution Pyrolysis Gas Chromatography

Ethylene-propylene-diene rubbers (EPDMs) are now used for various purposes because of their excellent resistance to ozone, weather, and heat. Therefore, many kinds of EPDMs are provided as commercial polymers. Consequently, reliable methods for the structural characterization of EPDM have been needed in the fields of material development, process control, and quality assurance of the cured products. The iodine value method is generally used to determine the diene content in EPDMs. However, it is too time consuming to be a routine method. Until now, spectroscopic methods such as IR and NMR are generally used for the study of the composition and the sequence length distributions in EPDMs. Levine and Haines determined the content of ethylidenenorbornene (ENB) in ethylene-propylene-ethylidenenorbornene rubbers (ENB-EPDMs) by IR. Florence and Loustalot investigated ethylene-propylene-1.4-hexadiene rubbers by NMR. However, these spectroscopic methods often encountered the difficulties in the analysis of vulcanized rubbers since they were insoluble and usually contained many kinds of additives such as curing agents, plasticizers, stabilizers, and fillers. On the other hand, owing to the recent development of excellent pyrolyzers and highly efficient fused-silica capillary columns, pyrolysis-gas chromatography (PyGC) has become a powerful tool to give unique information about structures of high polymers. Furthermore, PyGC is advantageous to the practical analysis of insoluble polymeric materials such as vulcanized rubbers.