Synthesis and Characterization of Olefin Copolymers as Viscosity Modifiers for Engine Oil

Microstructural properties of olefin copolymers (i.e., copolymer composition, sequence distribution, and molecular weight and its dispersity) are key factors, which affect the behaviour of olefin copolymers as viscosity modifiers in engine oil. In this article, the variation procedure and control methods of these specifications are described for the synthesis of olefin copolymers using soluble Ziegler-Natta catalyst in a semibatch reactor. Solution copolymerization of ethylene/propylene was performed using VOCl3-Al2Et3Cl3 systems. Finally, the synthesized viscosity modifier was characterized by IR, GPC, 13C NMR, DSC, and XRD techniques and elemental analysis method. Molecular weight was controlled by continuous feed of hydrogen during the reaction and its narrow dispersity was maintained by catalyst specifications and initial saturation of solvent by monomers. Although catalyst activity varies with time, 13C NMR and IR results demonstrated steady copolymer composition. This was achieved by using a catalyst system with mostly single active site in a semi-batch polymerization by feeding monomers continuously. Also, it was found that randomness in the microstructure of the copolymer was induced at a specific monomer ratio.