Effect of Polymer End Group on the Morphology of Polystyrene/Poly(methyl methacrylate) Composite Particles Prepared by the Solvent Evaporation Method

The effect of polymer end group on the morphology of polystyrene (PS)/poly(methyl methacrylate) (PM MA) composite particles was investigated on the basis of experimental observations and theoretical predictions. Both polymers with potassium persulfate (KPS)-derived hydrophilic end group(s) and 2,2'-azobis(isobutyronitrile) (AIBN)-derived hydrophobic end group(s) were synthesized by emulsifier-free emulsion polymerizations and solution polymerizations, respectively. Composite particles with the same end groups were prepared by release of toluene from PS/PMMA/toluene (1/1/24, w/w/w) droplets dispersed in an aqueous solution of sodium dodecyl sulfate (SDS). At a low SDS concentration, when the polymers with KPS-derived end group(s) were employed, acornlike particles were formed. On the other hand, when the polymers with AIBN-derived end group(s) were used, particles having a dimple were obtained. The interfacial tensions between toluene solutions of the polymers and SDS aqueous medium were lower for KPS-derived end group(s) than for AIBN-derived end group(s), and the difference was much larger for PS phase than PMMA phase. The predicted morphologies obtained from calculation of the minimum total interfacial free energy using the interfacial tensions agreed well with the experimentally observed morphologies in both cases. Moreover, the morphology of PS/PMMA composite particles with different end groups was also examined.