ATRP mediated encapsulation of Gibbsite: fixation of the morphology by using a cross-linker

Abstract

Using ethylene glycol dimethacrylate (EGDMA) as a cross-linker Gibbsite platelets were successfully encapsulated fully using an ATRP-mediated emulsion polymerisation technique. Previously we reported a "muffin-like" morphology, which was obtained using the same approach without a cross-linker. This morphology was attributed to the mobility of the growing polymeric chains, allowing them to move one side of the platelet during the reaction. The addition of EGDMA reduces this mobility and it is shown that this approach indeed leads to encapsulated Gibbsite. A comprehensive study of the reaction conditions, in particular the cross-linker addition profile and concentration, was carried out in combination with cryo-TEM characterization of the final particle morphology.Scheme 1 Schematic illustration of ATRP-based synthesis of polymer-Gibbsite nanocomposites using an anionic co-oligomer as a stabiliser and macroinitiator. † Electronic supplementary information (ESI) available: Experimental and characterisation details. See

Polymer Encapsulation of Single Clay Platelets by Emulsion Polymerization Approaches, Thermodynamic, and Kinetic Factors

“…The peanut morphology is where two deformed latex particles seem to be connected by a single clay platelet (Figure c). Also clay particles with only one side covered can be seen in some samples, we coin this morphology the muffin morphology (Figure d).…”

“…This mechanism is supported by the kinetic studies of Bourgeat‐Lami and co‐workers . Other mechanisms with which one can direct the polymerization to the surface are modification with polymerizable groups, adsorption of RAFT, or ATRP oligomers followed by chain extension hemimicelle formation on hydrophobically modified clay or through adsorption of bilayers.…”

“…Both conventional and RAFT radical polymerization have been applied in emulsion polymerization. Like in miniemulsion polymerization, the use of ATRP is scarce although also some work is ongoing in that direction …”

“…An interesting example is given by Chakrabary and Singha where the use of neutral functional monomer, in combination with a fluorinated acrylate in miniemulsion polymerization, led to encapsulated Cloisite hybrid latex particles (multiple clay platelets per particle) whereas the use of a positively charged functional monomer led to armored morphology. In emulsion polymerization, one would like to create an affinity of the monomer for the clay particle surface, this is typically done by creating a hemimicelle around the clay, using surfactant absorption on a more or less hydrophobized clay surface . Unfortunately, complete hydrophobization will lead to stacking of the clay platelets again because of the loss of favorable interactions between the clay surface and water that have led to the spontaneous exfoliation in the first place.…”

Design and Preparation of Highly Filled Water‐Borne Polymer–Gibbsite Nanocomposites

“…The discovery of a reversible addition‐fragmentation chain transfer (RAFT)‐mediated encapsulation method for filler materials, however, caused a significant shift in encapsulation strategy and many examples now exist in which this method was applied successfully . We recently extended this method to an atom transfer radical polymerization (ATRP)‐based method, which only in the presence of a cross‐linker led to encapsulated particles; without cross‐linker so‐called “muffin‐structures” were obtained . Realizing that the charged, reactive, oligomers used in both the RAFT and ATRP approaches in first instance act as stabilizers for the initial clay dispersion and subsequently for the polymer particles, we then used the charged oligomers as unreactive surfactants in a conventional starved‐feed emulsion polymerization .…”