Polymerization Parameters of Methacrylic Acid Esters as Viscosity Index Improvers in Lubricants

 A wide range of additives can be utilized to create desirable properties in lubricants. Polymers, as viscosity index improvers, are important additives in oils to improve their viscosity at different temperatures. Polymethacrylic esters due to their structural properties in comparison with other polymers are the best choice as special lubricants. The synthesis and solution polymerization of methacrylate esters have been conducted to end use as viscosity index improver in lubricants. Methacrylic acid esters were synthesized by reacting methacrylic acid with primary alcohols like hexanol, octanol, decanol and dodecanol in presence of sulfuric acid, heptane solvent and hydroquinone as a radical polymerization inhibitor. The structure of the synthesized esters was determined by spectroscopic methods. Further, the radical polymerization of these ester monomers was carried out in toluene. The effect of temperature, initiator amount and monomer percentages on molecular weight of polymers was investigated. The results show that by changing the initiator amount from 0.25 to 1.5%, the molecular weight of polyhexylmethacrylate at 6.8×104 was dropped to 2.9×104g/mol. Also, in polymerization reaction, it is shown that the molecular weight of poly(hexyl metacrylate) decreases with increasing temperature and the reduction in monomer content. TGA and DSC studies show that with increasing the length of the alkyl chain of the ester group, the thermal stability and glass transition temperature of the prepared polymers are decreased. By studying the rheological properties of polymethacrylate esters in two different base oils, the effect of polymer concentration and ester chain length was noted in relation to oil viscosity index.