Poly(n-Alkyl Itaconate-Co-Vinyl Acetate) as Pour Point Depressants for Lube Oil in Relation to Rheological Flow Properties

In the present work, poly(n-alkyl itaconate-co-vinyl acetate) comb-like polymers were synthesized by radical copolymerization of n-alkyl itaconates of various alkyl chain length and vinyl acetate monomers for use as pour point depressants in lubricant oil. Initially four n-alkyl itaconate monomers were synthesized by esterification of itaconic acid with a series of n-alkyl alcohol, having different alkyl chain length C16/C18/NAFOL 20 + A (Cav = 20)/NAFOL 1822 B (Cav = 22). The copolymerization of these monomers with vinyl acetate was then performed using dibenzoyl peroxide in toluene at 120°C up to high conversion, with molar ratios of 0.25:0.75, 0.50:0.50, and 0.75:0.25 for alkyl itaconate: vinyl acetate. All products were characterized by FTIR, 1H NMR and gel permeation chromatography (GPC). These copolymers were tested in terms of their suitability as pour point depressants and flow improvers for lube oil. The obtained data revealed that the prepared compounds depress the pour point of the lube oil successfully and the additive efficiency on the pour point reduction of the lube oil increases by increasing the concentration of these additives and by decreasing the alkyl chain length of n-alkyl itaconate. The rheological properties of lube oil (with and without copolymer additive) were studied in term of shear rate, shear stress and viscosity. The results indicated that the performance of flow improver was dependent on the copolymer compositions and the size of alkyl chain length of n-alkyl itaconate monomers. Poly(hexadecyl itaconate-co-vinyl acetate) with high content of vinyl acetate showed the best flow improver properties of lube oil. Comparison of morphologies and structures of wax crystals or aggregates in untreated and treated lube oil was also done by micro photographic studies which showed the modification in wax crystal morphology due to additives.