Polymethacrylate Viscosity Modifi ers and Pour Point Depressants 317
11.1.4 DEVELOPMENT OF OTHER APPLICATIONS
Another important application area for PMA chemistry is in the fi eld of pour point depressants (PPDs).
When a methacrylate polymer includes at least some longer alkyl side chains, relatively similar to the
chain length of waxes normally present in mineral oil, it can interact with growing wax crystals at suf-
fi ciently low temperatures. Wax-like side chains can be incorporated into a growing wax crystal and
disrupt its growth. The net effect is to prevent congealing of wax in the oil at the temperature where
it would have occurred in the absence of a PPD. Early PMA PPDs were used fi rst by the military and
later by civilian industry when Rohm and Haas offered such products to the industrial and automotive
markets in 1946. Although PMAs were not the fi rst materials used as PPDs (alkylated naphthalenes
were), PMAs are probably the predominant products in this particular application now.
Another use of wax-interactive PMAs is as refi nery dewaxing aids. The process of dewaxing
is carried out primarily to remove wax from paraffi nic raffi nates to lower the pour point of the
resulting lube oil base stocks. PMA dewaxing aids are extremely interactive with waxes found in
raffi nates and thus function as nucleation agents to seed wax crystallization and promote the growth
of relatively large crystals. The larger crystals are more easily fi ltered from the remaining liquid
so that lube oil throughputs and yields are improved, whereas pour points are lowered by virtue of
lower wax concentrations.
Incorporating monomers more polar than alkyl methacrylates into a PMA provides products
useful as ashless dispersants or dispersant VIIs. The polar monomer typically contains nitrogen
and oxygen (other than the oxygen present in the ester group), and its inclusion in suffi cient con-
centration creates hydrophilic zones along the otherwise oleophilic polymer chain. The resulting
dispersant PMAs (d-PMAs) are useful in lubricants since they can suspend in solution what might
otherwise be harmful materials ranging from highly oxidized small molecules to soot particles.
PMAs have also been used in a number of other petroleum-based applications albeit in rela-
tively minor volumes. An abbreviated list would include asphalt modifi ers, grease thickeners,
demulsifi ers, emulsifi ers, antifoamants, and crude oil fl ow improvers. PMAs have been present in
lubricants for about 65 years now, and their longevity stems from the fl exibility of PMA chemistry
in terms of composition and process. Evolution of the original lauryl methacrylate composition
to include various alkyl methacrylates and nonmethacrylates has brought additional functionality
and an expanded list of applications. Process chemistry has also evolved such that it can produce
polymers of almost any desired molecular weights (shear stability) or allow the synthesis of complex
polymer architectures. The evolution of effi cient processes for controlled radical polymerization in
the 1990s has led to the development of taper and block copolymers and has permitted the develop-
ment of products with narrower molecular weight distribution.
- 2 CHE MISTRY
- 2 .1 GENERAL PRODUCT STRUCTURE
Typically, a methacrylate VII is a linear polymer constructed from three classes (three dis-
tinct lengths) of hydrocarbon side chains. These would be short, intermediate, and long-chain
lengths. A more extensive discussion is given in Section 11.3, but an abbreviated description
is given here to better understand the synthesis and chemistry of methacrylate monomers and
polymers.
The fi rst class is short-chain alkyl methacrylate of one to seven carbons in length. The inclusion
of such short-chain materials infl uences polymer coil size particularly at colder temperatures and
thus infl uences the viscosity index of the polymer in oil solutions. The intermediate class contains
8–13 carbons, and these serve to give the polymer its solubility in hydrocarbon solutions. The long-
chain class contains 14 or more carbons and is included to interact with wax during its crystalliza-
tion and thus provide pour point depressing properties.