Antiwear performance of polysiloxane-containing copolymers at oil/metal interface under extreme pressure

Copolymers separately containing polysiloxane, thiophosphate-polysiloxane, thiophosphate-amino, and polysiloxane-amino groups were synthesized by free radical copolymerization. The antiwear behaviors of the synthesized copolymers as an oil additive in base oil were assessed with a wear tester by measuring the oil temperature, frictional coefficient, and electrical contact resistance between the two metal surfaces. Thiophosphate-containing copolymers were noted to limit the increase in the oil temperature and reduce the frictional coefficient by adsorbing the thiophosphate group onto the metal surfaces and then reacting on those surfaces. The oil temperature and the frictional coefficient of thiophosphate-polysiloxane-containing copolymer were lower than that of other synthesized copolymers before chemical adsorption by the thiophosphate group, which was resulted from the protection by the polysiloxane structure. The amino-polysiloxane-containing copolymer that settled on the metal surfaces by adsorbing the amino group reduced the frictional coefficient and limited the increase in the oil temperature caused by the presence of the polysiloxane group. Nevertheless, the amino-polysiloxane-containing copolymer physically adsorbed onto the metal surfaces at a low temperature and desorbed from the metal surfaces with increasing oil temperature.