engleski

Lubricating mineral oil additives based on styrene and alkyl methacrylate terpolymers

The applied rheological properties of the prepared polymeric additives on the base of styrene, dodecyl methacrylate and octadecyl methacrylate in the composition range up to 25 % of styrene, in the base mineral oil solutions were examined. In addition, terpolymerization reaction was thoroughly investigated. The low conversion terpolymers showed good agreement between experimental and theoretical copolymer composition data, calculated from the Alfrey-Goldfinger equation. The conversional heterogeneity and lines of the unique and binary azeotropic compositions were established. The terpolymerization process conditions were optimized by means of a series of experiments. The overall conversions of the monomers were estimated by 1H NMR spectroscopy while molecular weights by size exclusion chromatography. The high conversion polymerizations as 50 wt. % solutions of the monomer mixture in base mineral oil, were carried out in the isothermal reaction conditions at 100 oC, with peroxide initiation. Increasing the styrene content in monomer mixture, both, the initial reaction rate and molecular weight of obtained terpolymers are decreased. The properties of the prepared polymer additive solutions in base mineral oil were evaluated by kinematic viscosity, viscosity index, shear stability and pour point determinations, and compared with commercially methacrylate based additives (PAMA). It has been found that the kinematic viscosity does not change significantly by terpolymer composition and shows the ordinary linear dependence on molecular weight. The increase of styrene content in the additive resulted in a slightly decrease of viscosity index from 180 to 150, whereas the shear stability index also linearly decreased, reflecting the higher thermal stability of styrene based copolymers. However, the pour point temperature increases at first slightly from -33 oC to -27 oC (wST = 15 %) and then sharply to -9 oC (wST = 25 %). Based on the ratio of specific viscosities at 40 and 100 oC (Q factor), the value of 0.95 was obtained which is very close to that of PAMA (Q = 1.04) showing the same thickening effect at different temperatures. The obtained results demonstrated that efficiency of additives based on styrene / methacrylate terpolymers is fully comparable with pure methacrylate additives and give the prospects for their properties optimization by composition and structure changing.

lubrication; mineral oil; additives; styrene; alkyl methacrylate; terpolymerization

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