PHOTODEGRADATION OF POLY[ETHYLENE-CO-PROPENE-CO-(5-ETHYLIDENE-2-NORBORNENE)] RUBBERS .1. REAPPRAISAL OF THE PHOTOOXIDATION MECHANISM UNDER ACCELERATED CONDITIONS

In this work the reexamination of the photo-oxidation mechanism of three poly(ethylene-co-propene-co-5-ethylidene-2-norbornene) (EPDM) terpolymers containing different amounts of 5-ethylidene-2-norbornene (ENB)a) (2-8 wt.-%) is discussed. The photo-oxidation depends on the initial content of ENB units in the chains. The formation of a band at 923 cm-1 is attributed to the CH out-of-plane deformation of a new double bond in terminal position in the ethylidene moieties. The presence of double bond migration suggests the. formation of stable tertiary hydroperoxides which show a new band at 870 cm-1. The kinetic behaviour of a band with similar spectral pattern in the UV at 235 nm has been correlated with double bond migration. The identification of photoproducts both by 2,4-dinitrophenylhydrazin and SO2 confirms the proposed spectroscopic assignments. The gel measurements of the studied terpolymers, and some comparisons with a poly(ethylene-co-propene) (EPR) copolymer having a similar ethylene to propene ratio, suggest that the presence of ENB can strongly influence both the photo-oxidation and the crosslinking yields of these rubbers.