Thermoreversible cross-linking of maleated ethylene/propylene copolymers with diamines and amino-alcohols

Maleated ethylene/propylene copolymers (MAn-g-EPM) were thermoreversibly cross-linked using diamines and amino-alcohols. Covalent cross-links are formed via the equilibrium reaction of the grafted anhydride groups with di-functional cross-linkers containing combinations of primary (1°) and secondary (2°) amines and alcohols, while a shift of the equilibrium at elevated temperatures may result in their (partial) removal. Materials cross-linked with cross-linkers containing two 2° amine groups (2°–2°) and 2° amine and alcohol groups (2°–OH) are repeatedly processable via compression molding without chemical changes, which is an improvement in reversibility compared to the previously-studied cross-linking reactions with diols, for which irreversible side reactions limited the reversibility to some extent. The use of 1° amine groups results in materials that are not reprocessable via compression molding, due to irreversible imide formation. The 2°–2° and 2°–OH materials have higher levels of cross-linking after remolding than the diol-cross-linked MAn-g-EPM, which results in significant differences in rubber properties. Fourier transform infrared (FTIR) spectroscopy suggested that the reprocessability of these materials is caused by a continuous, dynamic exchange between cross-linked and free groups. Finally, the use of cross-linkers containing 3° amine groups results in the formation of ionic interactions. These materials are easily reprocessable at temperatures as low as 125 °C and have significantly different properties than the covalently cross-linked materials, due to the occurrence of ion hopping.