Monitoring the degradation of a thermally aged EPDM terpolymer by 1H NMR relaxation measurements of solvent swelled samples

Abstract

1H nuclear magnetic resonance (NMR) relaxation times were investigated as a method for monitoring the degradation of polymeric materials. The properties of an ethylene–propylene–diene (EPDM) terpolymer, oven aged at 140°C, were first characterized by traditional mechanical and solution measurements including ultimate tensile elongation, tensile strength, tensile modulus, gel fraction, solvent uptake and density. The elongation and density results provided a characteristic lifetime for this material at 140°C. The other measurements demonstrated that the EPDM terpolymer undergoes predominately chain scission during the early stages of the degradation process and predominately cross-linking during the latter stages. 1H NMR spin–spin relaxation times, T2, of the solid polymer were insensitive to the degree of aging until the polymer was very heavily cross-linked after long exposure times. The 1H NMR T2s of the polymer swelled in deutero-chloroform were as sensitive to aging as any of the classical measurements cited above. The NMR measurements have the advantage of being rapid, requiring minimal amounts of sample and being applicable for unconventional sample forms such as films, foams and powders.