Organic and Organometallic Single Chain Polymer Nanoparticles as Viscosity Modifiers for Lubricating Oils

Lubricating oils are of paramount significance due to their role in the reduction of erosion-corrosion and energy losses, among others. Two basic requirements for lubricating oils: adequate viscosity and viscosity-temperature response, are achieved by adding polymers, known as viscosity modifiers, (VMs) to oil formulations. During service, the oil’s viscosity decreases, and the rate of viscosity drop with temperature increases, due to mechanochemically-induced scission of covalent bond/s in the polymer chains which results in fragmentation of the macromolecules. Since the rate of polymer degradation increases with the backbone length, the main tactic to minimize degradation is to increase the VM’s hydrodynamic size without increasing the main chain length. This goal is achieved nowadays by non-linear architectures, such as hyperbranch or star. However, even the state of the art VMs today, are still susceptible to mechanochemical degradation. Herein, we demonstrate a different approach for this problem: hindering the main chain`s cleavage by using covalent¹ or coordinative intramolecular cross-linkages, folding it to a single chain polymer nanoparticle (SCPN). Thus, when a certain bond cleaves in the folded chain, the result is not a “catastrophic failure” of the macromolecule. Moreover, the gradual scission of the bonds in the folded polymer gradually unfolds it, causing the SCPN to gain hydrodynamic size in response to shear forces. As a result, these SCPNs solutions display reduced viscosity loss, and, unprecedently, even viscosity gain, when subjected to strong shear forces. Whereas cleavage of C-C bonds is almost always irreversible, this is not the case for metal-ligand interactions. Thus, metallo-SCPN VMs could, ideally, show self-healing behavior, further extending the VM lifetime. We present preliminary results of such hairy particle VMs, with metallo-SCPN core.

_{1. A. Levy, F. Wang, A. Lang, O. Galant, C. E. Diesendruck, Angew. Chem. Int. Ed. 2017, 56, 6431.}