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

Abstract

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...

Gas Barrier Polymer Nanocomposite Films Prepared by Graphene Oxide Encapsulated Polystyrene Microparticles

“…[4][5][6][7][8] The preparation of randomly orientated montmorillonite nanocomposite films, prepared by emulsion polymerization, has been reported to enhance oxygen barrier properties by only 30.3% at 1 wt% concentration, thus highlighting the need to develop methods that allow for simultaneous control over orientation and exfoliation. 9 Control over the orientation of nanofiller has been achieved using emulsion polymerization by Heuts et al, who demonstrated the encapsulation of both natural (montmorillonite) [10][11] and synthetic (gibbsite) [12][13][14][15] clays. Using atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization they prepared co-oligomers, which function as both the nanoparticle stabilizer and as a macro-initiator or macro-chain transfer agent for polymer chain extension.…”

“…Control over the orientation of nanofiller has been achieved by using emulsion polymerization by Heuts et al, who demonstrated the encapsulation of both natural (montmorillonite) , and synthetic (gibbsite) − clays. Using atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain-transfer (RAFT) polymerization, they prepared co-oligomers, which function as both the nanoparticle stabilizer and as a macroinitiator or macro-chain-transfer agent for polymer chain extension. − Control over the particle morphology was reported via RAFT under starved fed conditions, where the clay sheets act as seeds for polymerization, forming anisotropic particles that align the nanoplatelets against the substrate in the cast film.…”

“…Control over the orientation of nanofiller has been achieved by using emulsion polymerization by Heuts et al, who demonstrated the encapsulation of both natural (montmorillonite) , and synthetic (gibbsite) − clays. Using atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain-transfer (RAFT) polymerization, they prepared co-oligomers, which function as both the nanoparticle stabilizer and as a macroinitiator or macro-chain-transfer agent for polymer chain extension. − Control over the particle morphology was reported via RAFT under starved fed conditions, where the clay sheets act as seeds for polymerization, forming anisotropic particles that align the nanoplatelets against the substrate in the cast film. Unfortunately, barrier analysis was not conducted of these highly oriented materials …”