Mechanochemical Degradation of Ethylene−Propylene Copolymers: Characterization of Olefin Chain Ends

We have examined chain ends in ethylene−propylene (EP) copolymers following high-temperature shearing in an extruder. New chemical structures, not present prior to shearing, corresponding to vinyl, vinylidene, and vinylene chain ends were observed via 1 H and 13 C NMR and FTIR spectroscopy. A compilation of the various types of olefin chain ends possible via main chain scission of EP was made and their 13 C chemical shifts were calculated and compared with experimental results. This comparison, in combination with the results of DEPT experiments, allowed the assignment of the olefin region of the 13 C spectrum. The mechanism of polymer shearing appears to be hydrogen abstraction followed by disproportionation via β-scission of the main chain radicals to form olefins. A strong preference was shown for abstraction of methine protons, presumably due to the stability of the tertiary radical intermediate, and main chain scission at the position β to a methyl group.