Thermoreversible covalent crosslinking of maleated ethylene/propylene copolymers with diols

Maleated ethylene/propylene copolymer (MAn-g-EPM) was thermoreversibly cross-linked using different routes, i.e. ionic interactions (ionomers), hydrogen bonding and a combination thereof. Microphase separation into polar MAn-rich aggregates occurs for MAn-g-EPM and all cross-linked materials, which act as physical cross-links. The cross-link density does not change upon modification, but the strength of the aggregates is significantly increased, resulting in improved mechanical properties. All materials except the potassium ionomer with high degree of neutralization (DN) could be remolded into homogeneous and smooth films without chemical changes, indicating that the cross-links are truly thermoreversible. A comparison of the mechanical properties, i.e. tensile properties and compression set at room temperature, for the different cross-linking routes showed that the poorest properties are obtained for hydrogen-bonded materials. The potassium ionomer with high DN has the best properties by far, but is difficult to process. Comparable mechanical properties are obtained for zinc ionomers, potassium ionomers with low DN and amide-salts, which combine ionic interactions and hydrogen bonding. The amide-salts have a distinct advantage in processing over the ionomers, since they can be compression molded at much lower temperatures, although high temperatures should be avoided because of irreversible imide formation.