Immobilization of EPDM chains on the surface of carbon black and network structure in the rubber matrix of filled EPDM rubbers were studied by low-field proton NMR experiments. Advanced NMR experiments unambiguously show strong immobilization of EPDM chain fragments on the surface of carbon black. The thickness of the immobilized EPDM–carbon black interfacial layer is estimated to be ≥0.6 nm. The average number of monomer units per adsorption site is approximately nine, which suggests preferential chain adsorption at the crystal boundaries of carbon-black particles. The adsorbed chain fragments form physical (adsorption) junctions restricting chain mobility in the rubbery matrix outside of the interface. The cross-link density in filled EPDM is determined as a function of the filler type and its amount. The contribution of adsorption junctions to the total cross-link density is moderate as compared to the density of chemical cross-links and entanglement density. The mechanically effective network density in carbon-black-filled vulcanizates is determined by analysis of the stress–strain curves on the basis of the dynamic flocculation model. Comparison of the network density as measured by NMR and mechanical experiments shows significant differences which helps in better understanding of the reinforcement mechanism of filled rubbers. The study demonstrates that a relatively small amount of strongly adsorbed chains impacts the stress–strain properties of filled elastomers significantly.

The microphase structure of ionomers based on an amorphous, maleated ethylene-propylene copolymer was investigated by using small-angle X-ray scattering (SAXS) and solid-state NMR experiments. It was shown that in this kind of ionomers grafted maleic anhydride, its salts with Zn 2+ and a fraction of EPM chain fragments form immobilized, ion-rich aggregates. Three types of EPM chain units with different mobility were detected in the ionomers and in the ionomer precursor, which can be attributed to chain units with low mobility forming aggregates surrounded by an interfacial layer, EPM network chains interconnecting these aggregates, and network imperfections such as dangling ends and chain loops. When the the degree of neutralization is increased, the average dimension of the immobilized aggregate remains almost constant, while the thickness of the interfacial layer with restricted mobility slightly increases. The size of the aggregates in MAn-g-EPM ionomers is significantly larger compared to other ionomers, and as a consequence, the number of acid groups within an aggregate is also larger. At 50% neutralization, the number of aggregates suddenly decreases. The changes in some macroscopic properties, such as compression set and tensile properties, are related to the morphology of the ionomers as determined by SAXS and NMR. When the degree of neutralization is increased, the properties of the materials change due to strengthening of the ionic aggregates.

Detailed information about the chemical role of the third monomer 5-ethylidene-2-norbonene (ENB) in EPDM during peroxide cross-linking has been obtained by use of MAS 13C NMR spectroscopy and 1H NMR T 2 relaxometry. Advanced 13C NMR techniques like INADEQUATE and TOCSY applied to a special EPDM grade with 13C-labeled ENB reveal a large number of new aliphatic and olefinic signals as well as indications for oxidation. The ENB unit is involved in cross-linking reactions not only (i) via addition of macroradicals to the pendent ENB unsaturation yielding aliphatic cross-link structures but also (ii) via combination of ENB-derived allyl radicals resulting in cross-link structures with intact unsaturation. The latter represents a novel pathway in the mechanism for peroxide curing of EPDM.

The objective of this study is the thermoreversible crosslinking of maleated ethylene/propylene copolymer (MAn‐g‐EPM) using the equilibrium reaction with diols. Covalent hemi‐ester crosslinks are formed via the reaction of anhydrides with alcohols, while an equilibrium shift at elevated temperatures may result in their removal. High conversions to hemi‐ester are obtained at low temperatures in the presence of p‐toluenesulfonic acid, whereas conversions are low at high temperatures. The presence of microphase‐separated aggregates acting as physical crosslinks was demonstrated for MAn‐g‐EPM and all crosslinked materials. The covalent crosslinks were only formed within the aggregates, resulting in stronger aggregates that persisted to higher temperatures. The tensile strength and elasticity were significantly improved upon increasing level of crosslinking, whereas the type of diol has less influence. The covalently crosslinked MAn‐g‐EPM was reprocessable via compression molding at temperatures above 175 °C. Irreversible diester formation occurred for the longer diols, but did not prevent reprocessing, while short diols evaporated. Both effects lowered the level of crosslinking, resulting in significantly changed mechanical properties. The reprocessability does not originate from an equilibrium shift, but from a dynamic exchange between crosslinked and non‐crosslinked functional groups, which allows crosslinks to disconnect and the corresponding chain segments to diffuse between aggregates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1810–1825, 2008