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Stable poly(styrene-co-2-ethylhexyl acrylate) latex particles with diameter less than 600 nm were prepared by the miniemulsion polymerization of Pickering emulsions stabilized with hexyl-functionalized cellulose nanocrystals (CNC-hexyl-COOHs). Polymer nanocomposites were fabricated by casting of the CNC-stabilized latex particles, and the thermomechanical properties and microstructures of the films were studied and related to the type and amount of stabilizer as well as the processing conditions. Compared to the latex films stabilized with low-molecular-weight sodium dodecyl sulfate (SDS) surfactant, or using a combination of SDS and carboxylic acid CNC-COOHs, films stabilized solely with the alkyl-functionalized CNC-hexyl-COOHs showed much higher storage moduli in the rubbery regime and lower water uptake. Scanning electron microscopy (SEM) revealed a CNC network structure that is formed by excluded volume effects of the latex particles, which concentrates the CNC-hexyl-COOHs into the interstitial space during solvent evaporation. This effect results in the formation of a percolation network at a lower CNC concentration within the latex composite films. The network can be further reinforced by increasing the concentration of CNCs through an “ex situ” process where CNC-hexyl-COOH-stabilized latex particles were mixed with CNC-COOH aqueous dispersions before film casting. The ability to replace low-molecular-weight surfactants in water-based latexes with alkyl-functionalized CNCs that are not only biosourced but also act as reinforcing agents offers an opportunity to expand the property profile of a variety of commercial products such as paints, coatings, and adhesives.
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Ab Initio Emulsion Atom‐Transfer Radical Polymerization
Abstract Stable latexes of poly(meth)acrylates with predetermined molecular weights, narrow molecular‐weight distributions, and controlled architecture were prepared by true ab initio emulsion atom‐transfer radical polymerization. Water‐soluble (macro)initiators in combination with a hydrophilic catalyst, Cu/tris(2‐pyridylmethyl)amine, initiated the polymerization in the aqueous phase. The catalyst strongly interacted with the surfactant sodium dodecyl sulfate (SDS), thereby tuning the polymerization within nucleated hydrophobic polymer particles. Long‐term stable latexes were obtained, even with SDS loading below 3 wt % relative to monomer. Block and gradient copolymers were prepared in situ. The reaction volume and solid content were successfully increased to 100 mL and 40 vol %, respectively, thus suggesting facile scale‐up of this technique. The proposed setup could be integrated in existing industrial plants used for emulsion polymerization.
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- Award ID(s):
- 1707490
- PAR ID:
- 10061795
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 57
- Issue:
- 27
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 8270-8274
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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