Rheological studies of non-aqueous poly methyl methacrylate dispersions stabilised using graft copolymer steric stabilisers

Steric stabilisers were synthesised via the copolymerisation of styrene with acrylic macromonomers. The macromonomers were prepared by end capping reactions of poly 2-ethyl hexyl acrylate (PEHA) prepolymer with vinyl containing species. Preliminary reaction routes proceeded via the use of oxalyl chloride to create an acyl chloride intermediate followed by end capping with hydroxy ethyl methacrylate. This process was found to be inefficient due to the moisture sensitivity of the acyl chloride. The second route involved the direct end capping of the PEHA pre-polymer with glycidyl methacrylate (GMA). Macromonomer conversion levels were improved for the GMA route via the use of high temperatures and tertiary amine catalysts. An optimum set of conditions was achieved using 1.4 diazabicyclo [2.2.2.] octane as the catalyst and a reaction temperature of 160 QC. Non aqueous dispersion polymerisations of methyl methacrylate were performed. The factors affecting particle size in both single stage and twin stage polymerisation schemes were studied. Increases in the particle sizes of these dispersions were observed with increases in the total monomer concentration and also with decreases in the total stabiliser concentration. Increases in the particle size could also be achieved by increasing the proportion of the total monomer in the seed stage of the twin stage reaction and also by decreasing the proportion of the total stabiliser in the seed stage. The importance of the role of the seed upon the final particle size was firmly established. The rheology of these non aqueous dispersions was studied over a range of concentrations and under increasing shear stresses. At Iow and intennediate volume fractions the dispersions were observed to be predominantly Newtonian. Non-Newtonian behaviour was only observed at the extremes of the shear stress ranges studied. At high volume fractions of the dispersions non-Newtonian behaviour was observed over the range of shear stresses studied. Maximum volume fractions (~m) were calculated for these dispersions using the Kreiger-Dougherty equation. When these dispersions were blended in size ratios of 2: 1 it was observed that 4>m could be increased due to improved particle packing efficiency.