The Science Behind Lubrizol's Asteric™ Viscosity Modifiers

Lubrizol was the first to introduce Asteric PMA viscosity modifiers to the lubricant industry in 2008. These polymers utilize conventional polymethacrylate monomers but have radial or star architecture vs. a linear structure common to all other PMA polymers.


The Asteric polymer’s radial structure provides two major performance advantages that help enable the next generation of fuel and energy efficient lubricants.

  • Higher viscosity index
  • Lower viscosity at cold temperatures

High viscosity index (VI) lubricants have been shown in laboratory and vehicle tests to provide better efficiency and fuel economy compared to conventional lubricants having the same kinematic viscosity at 100ºC. Asteric VM’s better VI and cold temperature performance also reduce or eliminate the need for PAO in the formulation.

The performance of Lubrizol's Asteric polymers has been recognized by OEMs and lubricant formulators and are currently being used in a variety of passenger vehicle transmission and mobile equipment applications worldwide.

Figure 3

RAFT – the science behind Asteric polymers

RAFT (Reversible Addition Fragmentation chain-Transfer) is the enabling technology behind Asteric polymers. RAFT is a form of controlled free radical polymerization. Industry groups and universities have conducted research into RAFT and other controlled radical polymerization technologies for many years but their work has been confined to the laboratory – until now. Lubrizol is one of the first, if not the first, in the world to bring this technology out of the lab and into commercial production.

RAFT is often referred to as “living polymerization” because it can be stopped and restarted at any time during the manufacturing process. This allows new or different monomers to be added at any time during the reaction, changing the composition of the polymer chains. It also permits different polymer architectures to be made which cannot be done using conventional polymerization.

RAFT polymerization has commercial and technical advantages over other controlled radical methods being developed:

  • Near complete consumption of reactants
  • Utilizes no metals or halogens
  • Applicable to a broad range of monomers including acrylates and methacrylates
  • Can be manufactured in existing polymerization equipment

RAFT utilizes a special polymerization control agent, known as a RAFT Chain Transfer Agent or “CTA”. This agentacts much like a policeman to “direct traffic” during the polymerization process.

The specific CTA technology used in Asteric™ polymers is a sophisticated trithiocarbonate compound developed and patented by Lubrizol’s Advanced Materials division and adapted for use in lubricating oil systems. Lubrizol scientists developed the first commercially viable manufacturing process for this RAFT agent and have proven the process with full commercial scale production.

Lubrizol is now exploring potential interest in this RAFT CTA in the polymer industry outside of lubricants in areas such as oil and gas production, paints and coatings and medical hydro-gels.

For more information on Asteric Viscosity Modifiers or RAFT, please contact your Lubrizol representative or email us at