The Synthesis of Novel Block Copolymers via Atom Transfer Radical Polymerisation for Use as Stabilisers in Non-Aqueous Dispersion Polymerisations

Colloidal polymeric particle dispersions have found many industrial applications, one of which is as the ‘ink’ particles within electrophoretic displays. Traditionally these displays have shown high resolution, increased battery life and excellent readability in sunlight, when compared with more commonly used displays, such as liquid crystal displays (LCDs). However, commercially available examples have only demonstrated black and white displays, or screens with coloured filters over the black and white particles, resulting in ‘washed out’ colours. The development of a full colour electrophoretic display holds great industrial potential to advance the field of electrophoretics, as well as available technology.

A stabiliser is required during the synthesis of said particle dispersions, in order to control the parameters of the particles, as well as to ensure they remain stable and do not aggregate or settle out. Numerous different stabilisers have been successfully employed, although each has disadvantages and difficulties associated with it. This work describes the development of a block copolymer stabiliser of poly(methyl methacrylate) and poly(octadecyl acrylate). The stabiliser itself was synthesised using controlled radical polymerisation techniques, namely atom transfer radical polymerisation (ATRP). ATRP allowed for the molecular weight, composition and distribution of chain lengths to be tailored to meet certain requirements. The stabilisers were then employed in non-aqueous dispersion (NAD) polymerisations, to synthesise dispersions of monodisperse, cross-linked and dyed particles, with good size control and spherical packing. Initial dispersions showed desirable characteristics for electrophoretic fluids, but exhibited a thermoresponsive gelation once allowed to stand for a period of time. The nature of this gelation process was investigated, before modifications were made to the structure of the stabiliser. This new stabiliser was then used in NAD polymerisations, which resulted in particles which still possessed all the desirable properties previously observed, without the gelation. These particles were then tested successfully for their application in electrophoretic displays.