Encapsulation of unmodified Gibbsite via conventional emulsion polymerisation using charged co-oligomers

Abstract

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

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

“…The development of the molar mass distribution during the reaction was followed using size exclusion chromatography (Figure b). Bimodal molar mass distributions, in which the cooligomer peak remains constant and a high molar mass peak gradually increases, were observed, which is in accordance with our previous work . These observations are consistent with a conventional emulsion polymerization and a mechanism in which the cooligomer stabilizes the initial Gibbsite platelets and the formed polymer particles.…”

“…Representative images of all samples are shown in Figure 6 . It is clear from these images that in experiments with low filler contents up to 10 wt% (Figure a–c) every single Gibbsite platelet is completely covered with a polymer layer; the same morphology was reported in our previous work . When increasing the Gibbsite amount (φ f = 20 and 35 wt%), however, encapsulated particles with more than one platelet were observed.…”

“…In order to increase the φ S and φ f using our previously reported encapsulation strategy, it is important to realize what limits these parameters in the approach followed thus far. All polymerizations have been carried out using a starved monomer feed to an aqueous dispersion of Gibbsite (G) containing initiator and a fixed amount of anionic cooligomer (S), which was higher than that roughly corresponding to two times the isoelectric concentration (required for a stable Gibbsite dispersion) and lower than that corresponding to the critical micelle concentration (cmc), to avoid secondary nucleation .…”

“…Hence, knowledge of the two constants C and φ allows for the determination of the maximum amount of monomer per gram of Gibbsite for given total amounts of cooligomer and Gibbsite via Equation . Here, we estimated these constants from experiments using previously established reaction conditions, in which we varied n S,T (below the cmc) and monitored the added monomer amount versus time until the coagulation points, i.e., the moment at which coagulation starts ( Table 1 , Figure 1 ).…”

“…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 . 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 …”