Elvira Vidović

Thermal Stability of Lubricating Oil Additives Based on Styrene and n-Alkyl Methacrylate Terpolymers

In this work the thermal stability of polymeric additives for the improvement of rheological behavior of mineral lubricating oils was investigated. The systems studied comprised methyl methacrylate (MMA)/dodecyl methacrylate (DDMA)/octadecyl methacrylate (ODMA) and styrene (Sty)/DDMA/ODMA terpolymers. The composition of the terpolymers was determined by the 1H nuclear magnetic resonance spectroscopy and molar mass distribution by the size exclusion chromatography. The thermal degradation of terpolymers was studied by the thermogravimetric analysis. Sty/DDMA/ODMA terpolymers exhibited an improved thermal stability in comparison with MMA/DDMA/ODMA terpolymers of the corresponding compositions. Thus, the temperatures of 50% weight loss were found to be 313°C and 363°C for MMA terpolymer and Sty terpolymer, respectively, where x (MMA) = x (Sty) = 30 mol%.

A Chromatographic Study of Shear Stability of Poly(styrene-co-alkyl methacrylate) Viscosity Modifier for Lubricating Oils

Shear stability of styrene, dodecyl methacrylate, and octadecyl methacrylate terpolymer of various molecular weights, as the rheology modifier of improved solubility, thermal and oxidation stability in mineral base oil, was investigated. Viscosity loss of the 5 wt% solutions caused by scission of macromolecules subjected to the high shear forces ranges between 15% and 27% for weight average molecular weights from 156000 to 252000. After the shear tests the number average molecular weights of polymer increases while weight and Z-average molecular weights decrease. As macromolecules of molecular weights above 700000 fully break the molar-mass dispersity decreases significantly, from starting at 2.34–2.79 down to below 1.8. A linear dependence between viscosity loss of terpolymer solutions and molecular weights was observed. The advantage of using the size exclusion chromatography to determine the stability of the polymer against mechanical shear directly and the viscosity loss indirectly was established.

Crystallization and Pour Point of Solutions of the Dispersant Poly(Styrene-Co-Methacrylate) Viscosity Modifiers in Lubricating Base Oil

ABSTRACT Dispersant viscosity index improvers were synthesized by free radical copolymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA), dodecyl methacrylate, octadecyl methacrylate, and styrene in solution of mineral base oil. Studies included the dependence of the pour point and low-temperature crystallization behavior (characteristic temperatures and enthalpies) of the solutions of these polymer viscosity modifiers (VMs) on the amount of dispersant comonomer, DMAEMA, in the copolymer, weight average molecular weight of the copolymer, and concentration of the polymer in oil. Incorporation of dispersant comonomer in poly(styrene-alkyl methacrylate) structure additionally decreases the pour point of its solutions even for a very small concentration: the pour point of the base oil reduces from −9 to −25°C and −33°C for the 0.1 and 0.5 wt% concentrations of polymer, respectively. For concentrated 50 wt% solutions the enthalpy of crystallization decreases linearly with a decrease in the long-chain alkyl methacrylate share in copolymer. There is no unambiguous correlation between the pour point and crystallization parameters of semidiluted and diluted polymer solutions obtained by differential scanning calorimetry.