Pour point depression II; Structure vs. activity

Abstract

With low molecular weight compounds, increasing the number of groups per molecule which interact with wax either by adsorption or cocrystallization was shown to be advantageous. A definite specificity of depressant for a given wax was noted and shown to be the result of equal solubilities. Although activity can be extended by virtue of mixed crystal formation, usefulness of low molecular weight materials is limited to blends containing highly crystalline waxes. Polymeric materials, on the other hand, are widely applicable. This is undoubtedly due to the fact that 1) polymers have no specific solubility; that is, they do not crystallize out of solution in their useful temperature range, especially when internally plasticized with a mixture of monomer types. As temperature decreases, different polymer segments become successively cocrystallizable and the range of activity is thereby extended. 2) Polymers have a multiplicity of cocrystallizable segments in each molecule, hence can direct crystal growth much more efficiently than can small molecules. The following features of polymer structure were investigated with regard to their effect upon depressant activity: 1) Molecular weight above a minimum of a few thousand has little effect. 2) The polymer backbone bulk or stiffness can change the (critical and important) effective average side chain length. 3) The spacing between polymer side chains has a mild effect upon depressant activity. 4) Non-solubilizing comonomers have a marked effect upon depressing ability, depending on their size, polarity, and the quantity present. 5) Polar or non-hydrocarbon material in a polymer has no positive value in protecting wax crystals or reducing oil adsorption since effective poly-alpha-olefin polymers have been synthesized.