The Synthesis of Copolymers for Self-Assembly in Non-Polar Solvents and Tribological Testing

Abstract

The synthesis and properties of block copolymers have long been an important field of research. Recently, the self-assembly of block copolymers in a solvent selective for one block and the resultant formation of nano-objects with a variety of morphologies has attracted a lot of attention. Throughout this work, block copolymers comprising a block prepared using non-polar dienes such as 1,3-isoprene and 1,3-butadiene have been prepared such that a second block, comprising highly polar functionalities can be dispersed in non-polar solvents. Taking a very ‘academic’ approach, block copolymers of isoprene and various methacrylates have been prepared by a change of mechanism polymerisation (CHOMP) where living anionic polymerisation (LAP) was used to prepare end-capped polyisoprene which was then used as a macroinitiator for the atom-transfer radical polymerisation (ATRP) of methyl methacrylate (MMA) or N,N-(dimethylamino)ethyl methacrylate (DMAEMA). The block copolymers were then dispersed into non-polar solvents by solvent-switching resulting in self-assembly into micelles with different morphologies which were characterised by TEM and DLS. The same block copolymers of isoprene and the aforementioned methacrylates were investigated as potential friction modifiers in lubricant formulations by dispersion into non-polar base oils. PI-b-PDMAEMA was found to be an effective friction modifier both in neat base oil and full lubricant formulations where many other competing, surface-active additives are present. These results were used to guide the development of a more commercially feasible synthetic route towards structurally similar polymeric additives. Thus a series of microstructural block copolymers of homopolybutadiene, comprising ‘blocks’ rich in the 1,4- and 1,2-microstructures respectively, was prepared by LAP. A selective ene reaction was then carried out with maleic anhydride, resulting in blocky, amphiphilic copolymers which were then reacted by imidisation to impart a tertiary amine functionality pendant to the polymer chain. These maleinised and imidised polybutadienes were also found to be effective friction modifiers, offering a potential route to a new, commercially-viable class of polymeric friction modifier.