Lubricant Additives

154 Lubricant Additives: Chemistry and Applications

low free-amine content and better engine test performance than dispersants made from conven-
tional polyamines.
Imide and ester dispersants are made by reacting polyamines and polyhydric alcohols with
alkenylsuccinic anhydrides. The reaction typically requires a reaction temperature between 130
and 200°C to remove the resulting water and complete the reaction [44]. As mentioned earlier,
imide dispersants are made by the use of polyalkylene polyamines, such as diethylenetriamine
and triethylenetetramine. Many polyhydric alcohols can be used to make ester dispersants.
These include trimethylolpropane, tris(hydroxymethyl)aminoethane, and pentaerythritol. When
one uses tris(hydroxymethyl)aminoethane as the alcohol, one can obtain an ester dispersant
with basicity. The reactions to make succinimide and succinate dispersants are depicted in
Figure 5.11.
The alkylphenol-derived dispersants are made by reacting an alkylphenol, such as polyisobutyl-
phenol, with formaldehyde and a polyamine [58,69]. The result is the formation of 2-aminomethyl-
4-polyisobutylphenol. The reaction of ammonia or an amine, formaldehyde, and a compound with
active hydrogen(s), such as a phenol, is called the Mannich reaction [70,71]. Hence, such disper-
sants are called Mannich dispersants. For making phosphonate dispersants, the common method
is to react the free acid with an olefi n epoxide, such as propylene oxide or butylene oxide, or an
amine [2,72,73]. These reactions are shown in Figure 5.12. Salts derived from the direct reaction
of amine and metal bases with olefi n-phosphorus pentasulfi de adduct are also known [74,75]. It
is important to note that structures in fi gures are idealized structures. The actual structures will
depend on the substrate (alkylphenol and alkenylsuccinic anhydride)-to-reactant (formaldehyde
and polyamines) ratio.
Because of the polyfunctionality of the succinic anhydride group and of the amines and
polyhydric alcohols, various dispersants can be made by altering the anhydride-to-amine or
anhydride-to-alcohol ratios. These dispersants differ not only in their molecular weight but
also in their properties. Polyfunctionality of the two reactants leads to dispersants, which have
molecular weights that are three to seven times higher than expected if the two reactants were
monofunctional.

OH OH

R

+ Polyisobutylene

Polyisobutylene + P 2 S 5

Phenol

Polyisobutylphenol

Polyisobutenyl

Polyisobutenylthiophosphonic and polyisobutenylphosphonic acids

or polyisobutenyl

Acid

Adduct

Phosphorus

pentasulfide H

2 O

S

P OH

OH

O

P OH

OH

FIGURE 5.7 Synthesis of alkylphenols and alkenylphosphonic acids.