Dendritic Macrosurfactant Assembly for Physical Functionalization of HIPE-Templated Polymers

Abstract

High-internal-phase emulsion-templated macroporous polymers (polyHIPEs) have attracted much interest, but their surface functionalization remains a primary concern. Thus, competitive surface functionalization via physical self-assembly of macrosurfactants was reviewed. Dendritic and diblock-copolymer macrosurfactants were tested, and the former appeared to be more topologically competitive in terms of solubility, viscosity, and versatility. In particular, hyperbranched polyethyleneimine (PEI) was transformed into dendritic PEI macrosurfactants through click-like N-alkylation with epoxy compounds. Free-standing PEI macrosurfactants were used as molecular nanocapsules for charge-selective guest encapsulation and robustly dictated the surface of a macroporous polymer through the HIPE technique, in which the macroporous polymer could act as a well-recoverable adsorbent. Metal nanoparticle-loaded PEI macrosurfactants could similarly lead to polyHIPE, whose surface was dictated by its catalytic component. Unlike conventional Pickering stabilizer, PEI macrosurfactant-based metal nanocomposite resulted in open-cellular polyHIPE, rendering the catalytic sites well accessible. The active amino groups on the polyHIPE could also be transformed into functional groups of aminopolycarboxylic acids, which could efficiently eliminate trace and heavy metal species in water.

Keywords: adsorption; dendritic macrosurfactant; functional surface; polyethyleneimine; porous organic polymer.

Figure 1

Chemical structures of polyethyleneimine (PEI) and typical oil-soluble PEI macrosurfactant. PEI contains thousands of repeat units, but only some are shown here for clarity.

Figure 2

Synthesis of PEI macrosurfactants with different shell densities and core structures [33].

Figure 3

(Left) When HPEI-DO (PEI alkylated by dodecyloxirane) in chloroform is shaken with anionic methyl orange (MO) and cationic methyl blue (MB) in water at pH 7, the anionic dye MO is transferred to the bottom chloroform layer, while the cationic MB remains intact in the upper aqueous layer. If the pH is increased to 12, then MO is released into the water layer. (Right) Charge-selective encapsulation is responsible for dye separation [32].

Figure 4

Schematic of dendritic macrosurfactants (PEI@PS)-mediated polyHIPE (A), adsorption of Congo Red by the polyHIPE (B), and (C) SEM micrograph of the polyHIPE [3]. Reproduced with permission from Ye et al., J. Mater. Chem. A; published by the Royal Society of Chemistry, 2015 [3].

Figure 5

Schematic of small surfactant (A), block copolymer (B), and (C) PEI macrosurfactant-mediated unit of an emulsion.

Figure 6

(A) Schematic of two routes for PEI macrosurfactant-mediated synthesis of gold nanoparticle-dictated polyHIPE: (a) chloroauric-containing water is dispersed in PEI-macrosurfactant-containing monomer and (b) water is dispersed in Au@PEI-macrosurfactant (gold nanocomposite)-containing monomer; (B) TEM micrograph of Au@PEI-macrosurfactant stabilized emulsion; and (C) SEM micrograph of polyHIPE with the surface dictated by gold nanoparticles [5]. The scale bar is 4000 nm (1000 nm inset) for (B) and 20 μm for (C). Reproduced with permission from Ye et al. J. Mater. Chem. A; published by the Royal Society of Chemistry, 2015 [5].

Figure 7

Schematic of PEI-macrosurfactant-mediated synthesis of aminopolycarboxylic acid-dictated polyHIPE. Reproduced with permission from Weng et al. Mater. Chem. Frontiers; published by the Royal Society of Chemistry, 2020 [57].