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The most widely used pour point depressants are methacrylate polymers. Even though they have been employed commercially for many years to depress pour points and improve flow, the exact mechanism by which they do it remains obscure. It is generally believed that they function by disrupting or preventing the formation of three-dimensional wax networks, leaving the amount of crystalline wax unaffected. This paper deals with differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis to study blends of methacrylate polymers with both model paraffinic compounds and a paraffin/microcrystalline wax to gain a better understanding of their interactions. Some important structural requirements for polymer-paraffin interaction with a bearing on pour point depression have been identified. It is also shown that the polymethacrylate can have an effect on the amount of paraffin or wax that can crystallize.

Two common internal combustion engine lubricant additives, overbased calcium sulfonate detergents and dispersant olefin copolymer (DOCP) viscosity index improvers, are shown to interact strongly, resulting in large (ca. 50%) increases in relative viscosity in hydrocarbon solutions. This viscosity increase is believed to result from bridging interactions from either physi- or chemisorption of DOCP functional groups onto the inorganic core of the sulfonate detergent colloid, with a resulting increase in effective polymer molecular weight. Viscometric properties of the detergent/DOCP interaction products, shear stability and the effect of competitive interactions with polyisobutenyl succinimide dispersant additives are described.