Effect of pendant distribution on the dispersancy of maleated ethylene propylene
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This study describes how changes made to the modification of a polyolefin affect the solution properties of these modified polyolefins in apolar solvents. The modified polyolefins of interest are maleated ethylene-propylene random copolymers (EP-MAH) reacted with N-phenyl-p-phenylenediamine (NP3D) to yield NP3D-EP-MAH. NP3D-EP-MAH is used as a dispersant by the oil-additive industry and solution properties such as self-aggregation, rheological behaviour, and its efficiency at stabilizing carbon black particles (CBPs) were investigated. The maleation of the polyolefin was characterized in terms of succinic anhydride (SAH) content and level of SAH clustering along the polymer backbone by FT-IR and UV-Vis absorption and steady-state and time-resolved fluorescence. The self-aggregation of the modified polyolefins was characterized in hexane by replacing NP3D with 1-pyrenemethylamine and using fluorescence to probe excimer formation between an excited and a ground-state pyrene. The rheological behaviour exhibited by the solutions of modified polyolefins was characterized from the viscosity profiles of the solutions obtained as a function of polymer concentration. Finally, the adsorption of the modified polyolefins onto CBPs was characterized by analysis of Langmuir isotherms, which yields both the equilibrium constant and the maximum coverage for the binding of the modified polyolefins onto CBPs. The conclusions reached in this thesis are that clustering of the SAH pendants along the EP backbone enhances the ability of the modified polyolefin to self-aggregate in apolar solution. In turn, self-aggregation led to enhanced thickening of the NP3D-EP-MAH solutions and stronger adsorption onto CBPs. This thesis establishes how the level of SAH clustering affects self-association and establishes its consequence on the rheological properties and adsorption isotherms of NP3D-EP-MAH samples in apolar solvents.