Polyether-Based Block Co(ter)polymers as Multifunctional Lubricant Additives

A series of polyether-based diblock copolymers were synthesized by sequential organocatalytic ring-opening polymerization (ROP) of either hexene oxide (HO) or octene oxide (OO) as the first monomer with propylene oxide (PO) as the second monomer. In addition, one triblock terpolymer of OO, PO, and styrene oxide (SO) was synthesized following the same method. The ROP was catalyzed by triethyl borane (TEB)/(phosphazene base t-BuP2) with eicosanol as the initiator. The resulting co(ter)polymers have a low polydispersity index and good solubility in hydrocarbon-based oils and are metal-free. By blending polyoctene oxide (POO) and polyhexene oxide (PHO) homopolymers with a Group II base oil (AramcoPrima 230) (2.5 to 5.0 wt %), the viscosity index (VI) increased from 100 to 160, and the thermal stability enhanced up to 50 °C. By using diblock copolymers, POO-block-poly(propylene oxide) (POO-b-PPO) and PHO-block-PPO (PHO-b-PPO), instead of the homopolymers, the VI and the thermal stability are almost the same, but the oil exhibits superior lubrication performance, with friction and wear decreasing up to 46 and 86%, respectively. The addition of the PSO block to the POO-b-PPO chain (POO-b-PPO-b-PSO) further improves the thermal stability but worsens the rheological and tribological properties (i.e., VI, friction, and wear) of lubricating oils.