The Effect of Controlled Polymer Architecture on VI and Other Rheological Properties

Controlled architecture polymers, including block copolymers, have been an area of interest for a number of years. Block copolymers have been shown to be useful as viscosity index improvers, for example; block copolymers of poly (dienes or hydrogenated dienes) and poly(styrene). However, anionic polymerization, the method used to produce commercial styrenic block copolymers, has limitations on the types of monomers that can be used. Controlled Radical Polymerization (CRP) uses a free radical initiating system and a polymerization controller. This technology results in block copolymers containing a wider range of monomer compositions and leads to predictable structures, molecular weights and polydispersities. Furthermore, these block copolymers can be produced using standard free-radical polymerization techniques by virtue of a new nitroxide capable of controlling a wide range of monomers including acrylic and methacrylic monomers. We have found that acrylic block copolymers formed via CRP, produce excellent viscosity index (VI) improvement in lubricating oils. These acrylic block polymers, in some cases, can exhibit greater than 50% viscosity index improvement as compared to random copolymers or other block compositions. Reported are the results of an experimental design study investigating the composition of the acrylic blocks, molecular weight, and block architecture (diblock, triblock, and gradient) on the resultant VI.