Hydrophilic porous polymers based on high internal phase emulsions solely stabilized by poly(urethane urea) nanoparticles

Stable oil-in-water (o/w) Pickering high internal phase emulsions (HIPEs) having an internal phase of up to 95 vol% were prepared with a low-energy emulsification method. A poly(urethane urea) (PUU) aqueous nanodispersion was used as aqueous phase. The PUU nanoparticles of the aqueous nanodispersion acted as a mechanical barrier, and prevented droplet coalescence in the Pickering HIPEs. In addition, open porous hydrophilic polymer foams were obtained by polymerization of the Pickering HIPEs, and the morphology of the foams were tailored by changing the oil:water ratio, PUU nanoparticle and NaCl concentrations. The method used herein provides a simple way to prepare morphology controlled hydrophilic polymer foams using o/w Pickering HIPEs as template.     

Stability of high internal phase emulsions with sole cationic surfactant and its tailoring morphology of porous polymers based on the emulsions

Stable w/o high internal phase emulsion (HIPE) using cetyltrimethylammonium bromide (CTAB) as the sole surfactant was prepared with long time further mixing of the emulsion after the addition of aqueous phase was completed, although it was generally considered the emulsion would be unstable according to Bancroft rule. The delta backscattering data of these emulsions showed that the further mixing enhanced the stability of the HIPE significantly, because a dram partial of monomers was initiated in the period of preparing the emulsion, which reduced the diffusion of CTAB from the oil phase to aqueous phase and increased the viscosity of the continuous phase. In addition, the morphology of polyHIPEs based on this type HIPEs was tailored. Increasing aqueous phase fraction resulted in the increase of pore volume which could be up to 24.0 ml/g. Increasing the polymerization temperature led to an increase in average void and interconnect diameter in the resulting porous materials. Additionally, the presence of additives, PEG and ethanol, in the aqueous phase was found to increase the average void diameter remarkably. The interconnect diameter of the materials could be controlled at constant pore volume by tuning PEG and ethanol concentration in the aqueous phase. It was suggested that coalescence was the dominant effect in determining the morphology of the polyHIPEs prepared in the presence of PEG, and Ostwald ripening was the major role in tailoring the morphology of the porous materials with ethanol.     

Macroporous materials from water-in-oil high internal phase emulsion stabilized solely by water-dispersible copolymer particles

Water-in-oil (W/O) high internal phase emulsions (HIPEs) were prepared by utilizing water-dispersible copolymer particle stabilizer, whose concentration in the internal phase could reach as high as 12.0 wt% (equivalent to 52 wt% relative to the continuous phase). Accordingly, the macroporous materials with high content of skeleton substance would be obtained by the dissolving of these copolymer particles into the continuous phase and without any chemical reaction. And the morphology, the density and the mechanical property of the macroporous materials could be easily tailored through varying the standing time after emulsification, particle concentration in the aqueous phase and the internal phase volume ratio.     

Photopolymerised methacrylate-based emulsion-templated porous polymers

Highly porous and interconnected methacrylate-based porous materials were prepared by photopolymerisation of the continuous phase of high internal phase emulsion (HIPE) templates. The rapid cure afforded by photopolymerisation effectively ‘locks’ the emulsion morphology prior to emulsion destabilisation, in comparison to thermally-initiated HIPEs of similar compositions. Contrary to expectation, it was observed that fully cured photopolymerised polyHIPEs could be prepared with a thickness of up to 35 mm, despite the severe opacity of the parent emulsions. This is attributed to a photofrontal polymerisation process, where radicals generated on the surface propagate rapidly through the bulk of the emulsion. Homogeneous, well-defined polyHIPE materials of up to 95% nominal porosity were obtained by photopolymerisation of HIPEs containing up to 30 vol.% glycidyl methacrylate (GMA) in the monomer phase (the remaining monomers and crosslinker are acrylates). Surprisingly, poly(ethylene glycol) methacrylate (PEG-MA), a nonionic monomer that is miscible with both emulsion phases, could be added to such HIPEs after preparation. On polymerisation, hydrophilic, water-wettable porous materials were obtained. Finally, it was also demonstrated that all-methacrylate HIPEs could be prepared and cured to yield GMA-containing polyHIPEs. These findings demonstrate the versatility of photopolymerisation for the preparation of emulsion templated porous polymers.     

Synthesis and in situ functionalization of microfiltration membranes via high internal phase emulsion templating

The continuous phase of high internal phase emulsions (HIPEs) can be polymerized to produce highly porous materials, known as polyHIPEs. The aim of this work was to synthesize polyHIPE microfiltration membranes having a hydrophobic bulk and a hydrophilic surface to enhance their performance. Therefore, in situ functionalization was performed through interfacial copolymerization of a hydrophobic monomer (butyl acrylate) in the continuous phase with a hydrophilic monomer (sodium acrylate) in the disperse phase. The functionalization of polyHIPEs was studied by using conductometric titration and Fourier transform IR spectroscopy. We show that the surface charge density of poly(butyl acrylate)‐based polyHIPEs can be controlled by varying the concentration of sodium acrylate in the disperse phase. PolyHIPE microfiltration membranes have higher intrinsic permeability (around 1.31 × 10^?8 m²) in comparison to conventional microfiltration membranes. The interfacial copolymerization of sodium acrylate increases the permeability of microfiltration membranes. In addition, the rejection of polyHIPE microfiltration membranes was studied for the separation of microalgae. © 2019 Society of Chemical Industry     

Reactive Surfactants for Achieving Open-Cell PolyHIPE Foams from Pickering Emulsions

PolyHIPEs, highly porous polymers synthesized within high internal phase emulsions (HIPEs), emulsions with over 74% internal phase, are of interest for applications such as absorbents, reaction supports, and tissue engineering scaffolds. Typically, the surfactant contents for HIPE stabilization are relatively high, ranging from 20 to 30 wt% of the external phase, with the monomers usually being the remainder. One drawback of using surfactants for these applications is the potential for leachables, necessitating intensive purification processes for their removal. Pickering HIPEs, HIPEs stabilized using amphiphilic solid nanoparticles that spontaneously migrate to the oil–water interface, can be used as an alternative HIPE stabilization strategy. Although nanoparticles can add surface functionality advantageous for the application, polyHIPEs from Pickering HIPEs often lack the interconnecting holes needed for the high permeability required for such applications. This work describes a successful approach for designing an HIPE stabilization system that is based on a combination of nanoparticles and reactive surfactants and that generates the desired surface functionality, an interconnected porous structure, and a low leachable content. Such an approach can extend the applicative utility of such polyHIPEs by circumventing the need for extensive purification.     

Porous polymers prepared via high internal phase emulsion polymerization for reversible CO2 capture

A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO₂ capture from air using the humidity swing. The effect of pore structure on the CO₂ adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO₂ compared to a commercial Excellion membrane with similar functional groups.     

Polymerized high internal phase emulsion monoliths for the chromatographic separation of engineered nanoparticles

PolyHIPEs of ethylene glycol dimethacrylate (EGDMA) and styrene/divinylbenzene were prepared by polymerization of water‐in‐oil high internal phase emulsions (HIPEs) within high pressure liquid chromatography (HPLC) columns. The columns were incorporated into a HPLC system affixed to an inductively‐coupled plasma mass spectrometer, and their potential for the separation of engineered nanoparticles was investigated. Triplicate injections of 5 and 10 nm gold particles injected onto a poly(styrene‐co‐divinylbenzene) polyHIPE column produced an average difference in retention time of 135 s. On a poly(EGDMA) column, triplicate injections of dysprosium containing polystyrene particles of 52 and 155 nm produced a difference in retention time of 8 s. In both cases the smaller particles eluted from the column first. Comparison, using scanning electron microscopy, of the polyHIPE columns after the separations, against freestanding monoliths produced from the same HIPEs, revealed no apparent change in the internal porous structure of the polyHIPEs. © 2015 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 132, 41229.     

Polystyrene/magnetite hybrid foams prepared via 60Co γ-ray radiation of high internal phase emulsions

In this study, polystyrene (PS) solid foam with cell size of about 1 um and low polydispersity is prepared via γ-ray radiation induced high internal phase emulsions (HIPEs) at room temperature. The density of the foams can be as low as 0.05 g/cm³. The kinetics and molecule weight of styrene (S) polymerizing in continuous phase of HIPEs is studied. It is found that the molecule weight is greatly lower than the PS obtained from the polymerization in dispersed phase of emulsion. In addition, the authors study the mechanical properties of solid foam. The compression resistance of solid foam obtained from radiation method is better than these obtained from conventional method. At the same time, magnetite is added into the dispersed phase when prepared the HIPEs to fabricate magnetite hybrid PS foam. The saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) of the hybrid foam are 25 emu/g, 15 emu/g, and 350 Oe, respectively. The results revealed that the hybrid foams have some superparamagnetic.     

两亲嵌段共聚物基高内相乳液模板的制备与应用研究进展

多孔聚合物材料具有孔隙率高、加工性能好、质量轻的特点,在化学工程、生物医学工程及环境工程等领域具有广阔的应用前景。高内相乳液模板法为多孔聚合物材料提供了一种简单高效的制备途径,且以此方法制备的多孔材料形状及结构可控,因而引起了人们的广泛关注。本文聚焦于两亲嵌段共聚物稳定的高内相乳液及其所制备多孔聚合物的最新研究进展。同时,介绍了该类型多孔聚合物材料在吸附分离、生物医学、能量存储及催化材料等领域的应用。最后,对该领域的未来发展进行了展望。     

Emulsion templated bicontinuous hydrophobic-hydrophilic polymers: Loading and release

Water absorption is often poor in hydrophobic polyHIPEs, porous polymers synthesized within high internal phase emulsions (HIPEs). This paper describes bicontinuous polyHIPEs, the simultaneous polymerization of hydrophobic monomers (external phase) and hydrophilic monomers (internal phase). Integrating hydrogels within polyHIPEs extended the release of water-soluble dye from 10 h to more than 10 days. PolyHIPE capillary action promoted the rapid distribution of water throughout the hydrogel. The diffusion pathway in this bicontinuous system was similar to diffusion through an assembly of polydisperse spheres. The copolymerization of the hydrophilic monomers with the monomers in the external phase enhanced the hydrophilicity of the scaffold, reduced the modulus of the hydrated polyHIPE, and reduced the tortuosity of the diffusion path. Pre-polymerization of the external phase reduced the extent of copolymerization, enhanced the modulus, sealed the interconnecting holes, reduced the capillary action, increased the tortuosity, and extended the release time to 3 weeks.     

Emulsion-templated porous polymers: A retrospective perspective

PolyHIPEs are porous emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). HIPEs are highly viscous, paste-like emulsions in which the major, “internal” phase, usually defined as constituting more than 74% of the volume, is dispersed as discrete droplets within the continuous, minor, “external” phase. The surge in polyHIPE research and development parallels that of porous polymers in general and reflects the increasing number of potential applications (reaction supports, separation membranes, tissue engineering scaffolds, controlled release matrices, responsive and smart materials, and templates for porous ceramics and porous carbons). This review focuses upon the research and development in polyHIPEs through the prism of the work in our laboratory. The review includes an overview of the developments in polymerization chemistry, in the types of monomers, in the types of stabilization, in the generation of more complex polyHIPE-based systems (e.g. interpenetrating polymer networks, hybrids, bicontinuous polymers), and in unusual materials systems such as water-retaining polyHIPEs and shape-memory polyHIPEs.     

Influence of Monomer Structure,Initiation, and Porosity on Mechanical and Morphological Characteristics of Thiol-ene PolyHIPEs

Combining high internal phase emulsion templating with thiol-ene click chemistry produces porous polymers with high yields and degradable ester linkages. This study compares the influence of the monomer functionalities (tri versus tetra), internal phase volume, and initiation type (photo versus thermal) on the morphological and mechanical properties of poly(high internal phase emulsions) (polyHIPEs). For the synthesis of the polyHIPEs pentaerythritol tetrakis(3-mercaptopropionate) (PETMP, tetrafunctional), trimethylolpropane tris(3-mercaptopropionate) (TMPTMP, trifunctional), pentaerythritol tetraacrylate (PETA, tetrafunctional), and trimethylolpropane triacrylate (TMPTA, trifunctional) are used. The main factors influencing the properties of the polyHIPEs are the monomer structures and the internal phase volume, while the initiation type influences the morphology of the trifunctional system (pore size and morphology type) resulting in an interconnected cellular morphology in all cases except in the case of the photopolymerization of the emulsion with 85 vol% of the internal phase. The average pore diameter of the trifunctional system ranges from 8.0 to 27.8 µm, while for the tetrafunctional system it ranges from 8.1 to 12.3 µm. The compression moduli of the trifunctional system range from 0.093 to 0.240 MPa and for the tetrafunctional system they range from 1.906 to 7.670 MPa. The compression moduli decrease with increasing internal phase volume (porosity).     

Synthesis of emulsion-templated porous polyacrylonitrile and its pyrolysis to porous carbon monoliths

PolyHIPEs are emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). The miscibility of acrylonitrile (AN) with water has made it difficult to synthesize PAN-based polyHIPEs. This paper describes the successful synthesis of PAN-based polyHIPEs by crosslinking through copolymerization with divinylbenzene (DVB), by stabilization with a polyglycerol polyricinoleate surfactant, and by initiation with both oil- and water-soluble initiators. The PAN-based polyHIPEs had porosities of over 86% and porous structures that were different from those of typical polyHIPEs. This paper also describes the production of porous carbon monoliths through the pyrolysis of these PAN-based polyHIPEs. Pyrolysis did not produce significant changes in the porous structures, which were quite similar to those of the original polyHIPEs. The porosities were around 95% and the carbon monoliths were largely macroporous and mesoporous, with some microporosity. These results indicate that PAN-based polyHIPE templates can be used for the a priori design of porous carbon monoliths.     

Ceramic foams and micro-beads from emulsions of a preceramic polymer

A commercially available solid silicone resin was dissolved in a solvent and emulsified via stirring in the presence of water and surfactant to form three different types of emulsions, namely water-in-oil (w/o), water-in-oil-in-water (w/o/w) and oil-in-water (o/w), by following different preparation procedures. After curing, thermosets possessing different morphologies, ranging from highly porous (monolithic) foams to porous micro-beads and solid micro-beads, formed. The samples kept their shape upon pyrolysis, and resulted in ceramic foams (via w/o) and porous micron sized (∼200 μm) spherical particles (via w/o/w) having more than 80 vol% of total porosity, while with o/w emulsification solid SiOC ceramic particles with an average diameter of ∼100 μm formed. Both surfactant and water altered the IR spectra for emulsion-derived thermoset samples, in comparison to the pure cured resin, but upon pyrolysis similar amorphous ceramics were obtained from all samples.     

PolyHIPEs: Recent advances in emulsion-templated porous polymers

Porous polymers with well-defined porosities and high specific surface areas in the form of monoliths, films, and beads are being used in a wide range of applications (reaction supports, separation membranes, tissue engineering scaffolds, controlled release matrices, responsive and smart materials) and are being used as templates for porous ceramics and porous carbons. The surge in the research and development of porous polymer systems is a rather recent phenomenon. PolyHIPEs are porous emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). HIPEs are highly viscous, paste-like emulsions in which the major, “internal” phase, usually defined as constituting more than 74% of the volume, is dispersed within the continuous, minor, “external” phase. This review focuses upon the recent advances in polyHIPEs involving innovations in polymer chemistry, macromolecular structure, multiphase architecture, surface functionalization, and nanoparticle stabilization. The effects of these innovations upon the natures of the resulting polyHIPE-based materials (including bicontinuous polymers, nanocomposites, hybrids, porous ceramics, and porous carbons) and upon the applications involving polyHIPEs are discussed. The advances in polyHIPEs described in this review are now being used to generate new families of porous materials with novel porous architectures and unique properties.     

Post polymerisation hypercrosslinking of styrene/divinylbenzene poly(HIPE)s: Creating micropores within macroporous polymer

Porous copolymers of styrene and divinylbenzene (DVB) were prepared by emulsion templating using high internal phase emulsions (HIPEs) as precursors for monoliths. The ratio of monomers was varied in order to obtain samples with different degrees of crosslinking and different amounts of unreacted vinyl groups originating from DVB. PolyHIPE monoliths were subjected to reswelling and treatment with a radical initiator. Significant enlargement of the amount of meso- and micropores in the material was found resulting in a substantial increase of BET surface area, up to 7.2 times compared to untreated polyHIPEs. The treated PolyHIPE monoliths retained the open macroporous morphology typical of polyHIPE materials. Solid state ¹³C NMR experiments were used to determine the amount of unreacted vinyl groups in polyHIPE samples, both before and after the hypercrosslinking treatment.     

Porous hollow fibers with controllable structures templated from high internal phase emulsions

A technique to fabricate hollow fibers with porous walls via templating from high internal phase emulsions (HIPEs) has been demonstrated. This technique provides an environmentally friendly process alternative to conventional methods for hollow-fiber productions that typically use organic solvents. HIPEs containing acrylate monomers were extruded into an aqueous curing bath. Osmotic pressure effects, manipulated through differences in salt concentration between the curing bath and the aqueous phase within the HIPE were used to control the hollow structures of polyHIPE fibers. The technique was used to produce porous fibers (with millimeter-scale diameters and micron-scale pores) having a hollow core (with a diameter of 50%–75% of the fiber diameter). Two potential applications of the hollow fibers were demonstrated. In vitro drug release studies using these hollow fibers show a controlled release profile that is consistent with the microstructure of the porous fiber wall. In addition, the presence of pores in the walls of polyHIPE fibers also enable size-selective loading and separation of functional materials from an external suspension.     

Preparation of monodisperse PMMA particles by dispersion polymerization of MMA using poly(styrene-co-methacrylic acid) copolymer as a steric stabilizer

Dispersion polymerization of MMA was conducted using poly(styrene-co-methacrylic acid) copolymer as a steric stabilizer in an aqueous methanol medium. Various composition copolymers were easily prepared with a conventional radical polymerization by changing the monomer ratios of styrene to methacrylic acid, and were employed as a steric stabilizer for dispersion polymerization. The copolymers prepared with monomer ratios of 1.25–1.50 were found to be suitable steric stabilizers for dispersion polymerization. A very small amount of copolymer (0.6 wt% based on MMA) could act as a steric stabilizer effectively to obtain monodisperse PMMA particles. The particle size decreased with increasing the solvent polarity from 4 to 0.14 μm.     

Methacrylic acid microcellular highly porous monoliths: Preparation and functionalisation

By polymerisation of high internal phase emulsions (HIPEs), containing styrene (STY), divinylbenzene (DVB) and methacrylic acid (MAA) in the continuous phase, highly porous polymers including carboxylic functional groups were prepared. The ratio of methacrylic acid to divinylbenzene was varied in order to obtain polyHIPEs with a different degree of crosslinking which influenced a surface area of the polymers, being substantially higher (185 m²/g) with a higher degree of crosslinking (51% DVB) than with a lower degree of crosslinking (24% DVB, 46 m²/g). Up to 90% porous samples were prepared and the optimum hidrophilicity-lipophilicity balance (HLB) of the surfactant was found to be around 4.8–4.9. Both thermal and photo initiation were used to induce polymerisation. The resulting polymers had an open cellular morphology with cavity diameters between 21.8 μm and 44.2 μm and with interconnecting pores between 2.2 μm and 5.0 μm. Monolithic supports were used for further functionalisation with thionyl chloride and multifunctional amines, namely 1,4-diaminobutane and 1,12-diaminododecane. The functionalisation degree with thionyl chloride was 76%.