Synthesis of controlled-structure sulfate-based copolymers via atom transfer radical polymerisation and their use as crystal habit modifiers for BaSO4

Atom Transfer Radical Polymerisation (ATRP) has been used to polymerise ammonium 2-sulfatoethyl methacrylate (SEM) in aqueous media using various poly( ethylene glycol) (PEG) macro-initiators to give a range of controlled-structure, sulfate-based block copolymers. Such PEG-SEM diblock copolymers are effective crystal habit modifiers for the in situ precipitation of BaSO4 in dilute aqueous solution. In the presence of the PEG-SEM copolymer, near-monodisperse, lozenge-shaped BaSO4 particles were obtained, depending on the relative block lengths. X-Ray diffraction and thermogravimetric analysis of these particles demonstrated that they are polycrystalline in nature and contain around 8% copolymer by mass. This compares with the characteristic polydisperse rectangular platelets of single crystal BaSO4 obtained in the absence of the copolymer. Control experiments suggest that, while only the SEM block interacts directly with the particle surface, the PEG block also plays an important role in controlling the crystal growth. Independent variation of the PEG and SEM block lengths therefore provides a subtle mechanism for controlling the morphology, size distribution and crystalline structure of the inorganic phase.