Copolymerization of 2-(perfluorohexyl)ethyl methacrylate with divinylbenzene to fluorous porous polymeric materials as fluorophilic absorbents
Graphical abstract
Introduction
In the past decades, porous materials have advanced a blooming progress from inorganic zeolites, mesoporous silica, porous carbon, to hybrid metal-organic frameworks (MOFs) and porous organic polymers (POPs) [1]. POPs, combining the properties of both porous materials and polymers, show a good prospect in the application of catalyst supports, drug carriers, adsorbents, electrode materials, etc [2]. As well known, organic materials usually present a characteristic of “softness” due to the ease of deformation of polymeric chains. Capillary pressure and high surface energy tend to close small pores by simple deformation of the framework and thus lose the microporosity. Enhancing the cross-linking degree and thereby yielding hard and rigid organic materials could be an efficient way to avoid pore collapse. Polymerization of monomers with stiff motifs and multiple polymerization groups is frequently used to prepare porous polymers, such as hyper-cross-linked polystyrene [3], polyaniline [4], melamine-based microporous polymer networks [5] etc.
Introducing functional groups with affinity to given molecules could be an alternative way to develop versatile porous adsorbents [[6], [7], [8]]. Fluorine, as the most electronegative element, firmly binds with carbon forming the stable bond of C–F. Perfluorinated alkanes have an affinity to CO2. Incorporation of fluorine groups into covalent triazine frameworks has been illustrated to not only enhance the gas adsorption capacities but also increase the kinetic selectivity for CO2/N2 separation [9,10]. Hayashi et al. synthesized pi-conjugated microporous polymers (CMPs) via direct arylation of fluoroarenes (1,2,4,5-tetrafluorobenzene or 1,3,5-trifluorobenzene) with 2,4,6-tris(4-bromophenyl)-1,3,5-triazine. CO2 capture capacity up to 16.75 cm3/g at 1.0 bar was achieved on the synthesized CPMs [11].
Computational and experimental evidences have confirmed the presence of specific C–F···F–C interactions, i.e. fluorophilicity, which can be utilized in the physisorption of compounds containing long chain perfluorinated ponytails onto a perfluorinated substrate [12]. Through the fluorine-fluorine interactions, fluorous solid-phase extraction (FSPE) has been developed to recover fluorous catalysts, isolate F-tag compounds from complex chemical or biological samples, and enrich fluorous compounds in the environment [[13], [14], [15], [16]]. Huang et al. [17] fabricated a highly fluorinated monolith (HFM) by using a fluorinated monomer of 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate copolymerized with dual cross-linkers (divinylbenzene and ethylenedimethacrylate). The HFM was used as adsorbent of multiple monolithic fiber solid-phase microextraction (MMF-SPME), which could effectively extract six fluorobenzenes from water, demonstrating the fluorophilic characteristic. Lately, they used the dodecafluoroheptyl acrylate and 4-vinylbenzyltrimethylammonium chloride as mixed functional monomers to synthesize monolithic adsorbent. By means of multiple interactions including fluorophilic and anion-exchange interactions, the monolithic adsorbent greatly improved the limits of detection for perfluoroalkyl phosphonic acids (PFPAs) in water and vegetable samples [18]. Xu et al. reported the capillary electrochromatography (CEC) separation of fluorous analytes on a fluorous porous polymer monolith (FPPM) stationary phase based on fluorous-fluorous interaction. Fluorous monoliths showed enhanced separation performance by providing better selectivity, higher resolution and shorter analysis time compared to a similar non-fluorous (reversed phase) monolithic column [19]. FPPM monoliths prepared using fluorous methacrylate as monomer and 1,3-butanediol diacrylate as cross-linker exhibit both fluorous and hydrophobic character [20].
Besides the incorporation of specific functionalities, pore engineering is the other consideration for improving the adsorption performance of porous materials. Wang et al. reported a high internal phase emulsion (HIPE) templating method to fabricate a porous fluoropolymer using polylactic acid (PLA) as co-stabilizer. The addition of PLA produced a porous material with narrower void size distributions, higher specific surface areas and enhanced mechanical properties. Yet the fluoropolymers prepared by the HIPE templating method showed very large pores (>1 μm), which would reduce the specific surface area and the adsorption capacity [21]. The free radical-initiated polymerization of a stiff cross-linker of divinylbenzene (DVB) could directly produce a nanoporous polymer of polydivinylbenzene (PDVB), as reported by Zhang et al., which displayed excellent adsorptive property for volatile organic compounds (VOC) and organic pollutants in water [22,23]. Nanoporous PDVB also finds application in the adsorptive removal of Rhodamine B from aqueous solution [24]. Crosslinking copolymerization of butyl methacrylate with a small amount of DVB could produce a highly oil-absorbing gel [25]. Lucas and coworkers reported porous resins based on copolymerization of methyl methacrylate (MMA) and DVB, which show highly efficient in removing naphthalene (NAF) [26]. DVB has been proved a good crosslinker for the construction of porous polymers.
Here we report a type of porous fluorinated polymeric material synthesized through a free radical-initiated copolymerization using 2-(perfluorohexyl)ethyl methacrylate (C6Rf) as the fluorous monomer and divinylbenzene (DVB) as the rigid crosslinker (Scheme 1). Hydrofluoroether, as a good solvent for C6Rf and its homopolymer, could induce the formation of porous structure. The fluorous porous poly methacrylate-divinyl benzene (FPMD) synthesized with DVB/C6Rf = 1 in molar ratio and hydrofluoroether as the solvent shows a selective absorption for the fluorous solvent, illustrating the fluorophility of porous fluorinated polymeric materials.
Section snippets
Chemicals
Divinylbenzene (DVB, 80%, mixture of meta- and para-isomers, 1000 ppm p-tert-butylcatechol as inhibitor) was supplied by Aladdin Co. Ltd., China. 2-(Perfluorohexyl)ethyl methacrylate (C6Rf, A.R.) was supplied from Suzhou Zhongbo Chemical Technology Co. Ltd., China. Hydrofluoroether 1-(ethoxy)nonafluorobutane (HFE-7200) and 1,1,1,2,2,3,4,5,5,5- decafluoro-3-methoxy-4-(trifluoromethyl)pentane (HFE-7300) were purchased from 3 M China. Azodiisobutyronitrile (AIBN, 99%) was purchased from J&K
Results and discussion
Divinylbenzene (DVB) is a conventional crosslinker in the polymerization. A free radical-initiated polymerization of DVB produces a porous polydivinylbenzene (PDVB) monolith with the same shape of the reactor (Fig. S1). As shown in Fig. 1, the PDVB monolith shows an isotherm of the combination of type I and II, indicating the existence of both micropores and macropores. The BET specific surface area is 846 m2/g. When introducing the fluorous monomer of 2-(perfluorohexyl)ethyl methacrylate
Conclusions
Porous fluorous polymeric materials have been synthesized through a free radical-initiated copolymerization of 2-(perfluorohexyl)ethyl methacrylate (C6Rf) and divinylbenzene (DVB) in a simple solvothermal synthesis system. The effects of the ratio of monomers and the type of solvent on the pore structure and absorption properties of fluorous porous poly methacrylate-divinyl benzene (FPMD) have been investigated. An increase of the molar ratio of C6Rf to DVB leads to a decrease and even
CRediT authorship contribution statement
Huiling Tang: Investigation, Writing - original draft. Yuehua Gou: Formal analysis, Methodology. Zhengdong Yan: Investigation, Resources. Qingqing Hu: Resources, Validation. Fumin Zhang: Formal analysis. Qiang Xiao: Conceptualization, Methodology, Formal analysis, Writing - review & editing. Yijun Zhong: Supervision. Weidong Zhu: Project administration, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
Financial support from the National Natural Science Foundation of China (21471131) is gratefully acknowledged.
References (31)
- et al.
Microporous Mesoporous Mater.
(2018) - et al.
Polymer
(2016) - et al.
Adv. Synth. Catal.
(2017) - et al.
J. Chromatogr. A
(2017) - et al.
Talanta
(2020) - et al.
J. Chromatogr. A
(2014) - et al.
Nano Today
(2009) - et al.
J. Environ. Manag.
(2015) - et al.
Solid State Sci.
(2014) - et al.
Chem. Rev.
(2012)
Chem. Soc. Rev.
Ind. Eng. Chem. Res.
Chem. Mater.
J. Am. Chem. Soc.
Ind. Eng. Chem. Res.
Cited by (2)
Removal of oils and organic solvents from wastewater through swelling of porous crosslinked poly(ethylene-co-vinyl acetate): Preparation of adsorbent and their oil removal efficiency
2023, Marine Pollution BulletinCitation Excerpt :Although three approaches namely physical, chemical and biological have been widely used in the removal of these contaminants from wastewater, owing to certain technical as well as economic drawbacks these approaches have become stagnant, and the use of polymeric composites as oil absorbents has gained wide popularity during recent times. Some of the most promising polymeric composites which are being widely used all over the world as oil absorbents are based on polyurethane (Li et al., 2012), poly(alkoxysilane)s (Ozan Aydin and Bulbul Sonmez, 2015), polypropylene (Li and Wei, 2012), polymethacrylate (Tang et al., 2020), and polystyrene (Lin et al., 2012). In this work, we have attempted to increase the porosity of C-EVA by adding sodium chloride (NaCl) into the polymer network as porogen and followed by leaching out of NaCl from the polymer matrix by water extraction.