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.