engleski

Influence of molar mass and styrene on thermal stability and phase transitions of methacrylate based polymer additives for lubricating oils

Polymers based on alkyl methacrylates are widely used as additives for modifying the rheology of lubricating oils, where they serve as viscosity thickeners, viscosity index improvers and pour point depressants. It was established that methacrylates with medium size lateral alky groups (C10-C14) enhance viscosity index and those with the long chain groups (C16-C18) mostly contribute to the lowering of the pour point of solutions, whereas the methyl group contributes to the stiffness of the polymer chain. Also, polymers for lubricating purpose should have high shear stress stability over broad temperature range as the conditions found in lubricating environment require. Thus, to have multiple functionalities, additives should have high thermal and oxidative stability which can be achieved by addition of styrene comonomer units. [1, 2] Free radical polymerizations of monomers were carried out at 95 °C in mineral base oil using tert-butyl- peroxy-2-etilhexanoate as initiator and n- dodecyl mercaptane as chain transfer agent. There are two groups of polymers containing same comonomers: N, N-dimethylaminoethyl methacrylate (DMAEMA), dodecyl methacrylate (DDMA) and octadecyl methacrylate (ODMA) differentiating in one comonomer: styrene (ST) and methyl methacrylate (MMA). Synthesized polymers of different molar mass and composition were analysed using differential scanning calorimetry to determine phase transitions (glass transition temperature, melting point and crystallization temperature). Also, thermogravimetric analysis was carried out to investigate thermal and oxidative stability.

lubricating oils ; polymer additives, thermal properties, DSC, TGA

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