The use of controlled radical techniques to form polymer architectures suitable for use as Gear Oil Viscosity Modifiers

Abstract

This project is concerned with the synthesis of Viscosity Modifiers (VMs) for use in gear box oils. The use of amines as precursors for initiators is also of interest due to their dispersant properties. Atom transfer radical polymerisation (ATRP) was used to prepare statistical copolymers of n-Butyl methacrylate and C12/15 methacrylate for use as VMs. These copolymers were first of a linear nature demonstrating that ATRP could be used to polymerise this monomer combination to give well defined polymers with a high degree of control. Thereafter, multi-functional initiators were used to synthesise core first stars with differing numbers of arms. Three, four, five and eight arm stars were successfully synthesised giving well defined polymers. These polymers were tested by Lubrizol for their viscometric properties. All were found to give significant improvements versus Lubrizol’s existing linear polymers in almost all respects. Although the core first stars gave a significant improvement in viscometric properties the costs of the core are relatively high for the application. Therefore the synthesis of arm first stars via ATRP was carried out. Design of experiment (DoE) was used to aid in the optimisation process and to interrelate any factors used in the design. The DoE process indicated two relationships between input factors, one of which was defined numerically. A range of polymers were synthesised on a larger scale for testing by Lubrizol for their viscometric properties. The polymers were found to have exceptional viscosity properties, compared to the baseline sample. The use of amines as precursors for initiators (forming amide initiators) was investigated. 4-Aminodiphenylamine (ADPA) was synthesised into an initiator suitable for ATRP and used in several polymerisations. It was found to have very low initiator efficiency. For this reason Single Electron Transfer Living Radical Polymerisation (SET-LRP) was employed to polymerise methyl acrylate from this initiator with near 100% initiator efficiency. A range of other amide initiators were also successfully used in polymerisations. A new solvent system for SET-LRP was also demonstrated. The addition of phenol to toluene promoted the disproportionation of Cu(I) allowing SETLRP to take place. Polymers were synthesised in this solvent mixture with high degrees of control over molecular weight with narrow Polydipersity indexs (PDI)