Determination of Ethylidenenorbornene in EPDM Terpolymers

Ethylidenenorbornene (ENB) is a diene often employed as the third monomer in the commercial production of ethylene-propylene terpolymers (EPDM). A number of spectroscopic, chemical, and physical property procedures were examined as potential methods for determining ENB content. These included the use of iodine monochloride (ICI) and borane chemistry, nuclear magnetic resonance (NMR), and infrared (IR) analyses, as well as refractive index determinations. To evaluate the accuracy and reproducibility of the various methods, we prepared 24 EPDM terpolymers containing carbon-14 labeled ENB. The labeled diene was prepared via the Wittig synthesis. The ENB content of the EPDM's varied from 1.17 to 17.40 weight per cent. Catalyst systems for terpolymer preparation were employed that were representative of those used commercially in the production of EPDM. The refractive index method was found to combine adequate precision with speed of operation and proved to be the most reliable of the methods studied for determination of ENB content. An iodine number method was equally precise but suffered from the standpoint of speed. Two IR methods employing the 1685 cm−1 and 805 cm−1 absorption bands were not acceptable because of various structural interferences arising from compositional variations within the polymers. Proton NMR requires the use of time averaging and borane. chemistry proves to be a more cumbersome wet method than ICI, although presumably it involves reactions with olefins less complicated by side reactions than with ICI. Interrelationships of the various techniques are examined with regard to information concerning branching reactions. It is concluded that the data are consistent with the idea that commercial EPDM is a highly branched, partially gelled polymer. The basic contribution here is the refractive index technique which we referred to previously.