An Alternate Approach of Cross-Linking XNBR via Ferric–Carboxylate Interaction Assisted by Dimethylaminopyridine
Suraj W. Wajge, Chayan Das
Abstract
Metal–ligand coordinated cross-linked polymer composites, which can alter the network topology via a dynamic bond exchange mechanism, have been recognized as promising candidates to overcome the shortcomings of conventional cross-linked composites such as poor recyclability and self-healing ability. In this letter, we present how the carboxylic functional group of carboxylated nitrile rubber (XNBR) is utilized to coordinate with ferric ions to produce a cross-linked rubber composite via a simple but efficient approach. This has been achieved by cross-linking of commercially available XNBR by direct physical mixing of it with ferric salt and thus eliminating the use of any solvent. The development of metal–ligand-interactive cross-links in the XNBR matrix is established by rheological and swelling studies. The use of a small amount of a heterocyclic base, dimethylaminopyridine (DMAP) is found to play a crucial role by influencing the extent of cross-linking between ferric and carboxylate groups. The proposed cross-linking mechanism is validated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential scanning calorimetry studies. Strong and favorable ferric–carboxylate coordination interaction and cluster formation are believed to provide reinforcement to the rubber composite to maintain adequate mechanical properties. In addition, the optimum composition of the composite is found to impart features like recyclability and weldability.