This paper describes the synthesis of anisotropic polymer–Gibbsite nanocomposites with “muffin-like” morphology via a starved-feed ATRP emulsion polymerisation.

A simple procedure for the encapsulation of unmodified Gibbsite was developed using conventional emulsion polymerization and charged oligomers as stabilisers.

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

The discovery of a reversible additionfragmentation chain transfer (RAFT)-mediated encapsulation method for filler materials, [12] however, caused a significant shift in encapsulation strategy and many examples now exist in which this method was applied successfully. [13][14][15][16][17][18][19][20] We recently extended this method to an atom transfer radical polymerization (ATRP)-based method, [21] which only in the presence of a cross-linker led to encapsulated particles; [22] without cross-linker so-called "muffin-structures" were obtained. [21] 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. [21] This procedure for the encapsulation of unmodified Gibbsite platelets involves the adsorption of (an excess of) anionic cooligomers of butyl acrylate and acrylic acid unto the cationic Gibbsite surface, followed by a conventional starved feed emulsion polymerization and is schematically shown in Scheme 1. [23] A clear effect of cooligomer concentration on the colloidal stability was observed and, as expected, only a limiting amount of polymer per Gibbsite platelet could be stabilized before colloidal instability occurred. [23] The obtained solids content (φ S ) in these studies was therefore rather low (i.e., φ S = 17 wt%) and had a very low filler content (φ f ) of 0.4 wt%, [23] see Appendix B for the definitions of φ S and φ f . Higher solids and filler contents, however, would be desirable for practical applications.Polymer-clay nanocomposites with a solids content as high as 50 wt% have been reported in the literature, but most of them were obtained with a relatively low filler content (≤3 wt%); [3,6] only a limited number of publications were dedicated to the preparation of highly filled polymer-clay particles. [3,24,25] These studies indicated that the compounds used for hydrophobization of clay [3,24] and the size of the clay platelets [25] can affect the maximum filler content and that the use of larger amounts of clay platelets may result in less colloidal stability because of an increase in ionic strength of the water phase. [26] It has also been observed that the morphology of the resulting nanocomposites was affected by the filler amount. [24] Overall, it can safely be concluded that the synthesis of highly filled polymer-clay nanocomposites with a controlled morphology still remains a challenge. NanocompositesHighly filled, high solids content, water-borne polymer-Gibbsite nanocomposites are prepared with Gibbsite contents as high as 35 wt%. The polymerGibbsite nanocomposites are synthesised via conventional starved feed emulsion polymerization using negatively charged butyl acrylate-co-acrylic acid oligomers, which functioned as electrosteric stabilizers for the initial platelets and the subsequently formed latex particles. A simple ma...

Summary: Water-borne anisotropic polymer-Gibbsite latex particles were prepared by a conventional and an atom transfer radical polymerisation (ATRP) based starvedfeed emulsion polymerisation without any chemical modification of the platelet surface. Anionic co-oligomers, synthesised via ATRP, were used in both approaches. In the conventional-based route charged co-oligomer acted as stabiliser for the initial platelets and the latex particles formed. In case of an ATRP-based approach the co-oligomer not only served as stabiliser, but also as a macroinitiator for Activator ReGenerated by Electron Transfer (ARGET) ATRP-based starved-feed emulsion polymerisation. Cryo-TEM characterization of the resulting nanocomposites showed successfully encapsulated platelets in the conventional-based approach and a "muffin-like" morphology in the ATRP-based one.