Water‐Soluble Ionic Liquid‐Containing Sulfur Polymers for Mercury Capture, Demulsification, and Antibacterial Activity

Sulfur polymers, prepared by inverse vulcanization using elemental sulfur and vinylic monomers, are emerging functional materials of current research interest; however, sulfur polymers suffer from limited water solubility due to the hydrophobic nature of conventional comonomers and sulfur. Herein, the preparation of ionic liquid (IL)‐containing sulfur polymers are reported using the hydrophilic ionic liquid, 1‐allyl‐3‐vinylimidazolium chloride (AVImCl) as a comonomer. The introduction of IL significantly enhances the hydrophilicity of sulfur polymers, enabling them to dissolve in water. Benefiting from the thorough contact with aqueous mercury ions, the resultant sulfur polymer possesses high uptake capacity (436 mg g−1). After binding mercury, a coordination complex is formed and precipitated. The charged sulfur polymers gain a new application in demulsification. The polymer quickly breaks oil‐in‐water (O/W) emulsions through anion exchange between Cl− of the polymer and dodecylbenzenesulfonate (DBS−) of the surfactant. In addition, the polymer has a growth inhibitory effect against Staphylococcus aureus. The integration of IL and elemental sulfur provides a novel approach to modifying the wettability of sulfur polymers. Also, this novel water‐soluble IL‐containing sulfur polymer, with mercury capture, demulsification, and antibacterial activity, can be considered as a multifunctional material in practical water purification.


Introduction
Sulfur polymers containing more than 50 wt.%sulfur can be prepared by inverse vulcanization, which was first reported by Pyun and co-workers in 2013. [1]Inverse vulcanization includes the polymerization of elemental sulfur with vinylic comonomers, for example, dicyclopentadiene (DCPD), [2,3] divinylbenzene (DVB), [4] 1,3-diisopropenylbenzene (DIB), [5][6][7] limonene, [8] styrene, etc. [9] The variety of comonomers endows sulfur polymers with enhanced electrochemical, [10] thermomechanical, [5] and optical properties, [11] gradually expanding the applications of sulfur polymers and thus turning sulfur waste into a valuable resource.So far, most of the sulfur polymers exhibit limited water solubility due to the hydrophobic nature of both sulfur and the comonomers used.This limitation may impede the use of sulfur polymers in waterrelated fields, such as heavy metal binding.Access to water-soluble sulfur polymers is desirable.Recently, Jenkins and colleagues synthesized charged polysulfides by polymerization of elemental sulfur and comonomer diallyl dimethylammonium chloride (DADMAC). [12]This polysulfide was found to dissolve in water and fully bind with aqueous metal ions, instead of solely relying on surface interactions.This water-soluble sulfur polymer offers an avenue of effective water remediation.
Ionic liquids (ILs) have received much attention due to their low vapor pressure, high viscosity, thermostability, and ionic conductivity, etc. [13] Among these characteristics, the tunable wettability of ILs has been studied in recent decades.In brief, the wettability can be controlled by the alkyl chain length of cation and anion species of ILs. [14,15]Mecerreyes and colleagues introduced imidazolium IL as segments into sulfur polymers through post-functionalization. [16] The obtained polymer displays anion-dependent solubility in water: it is soluble when the anion is chloride, but insoluble in water when the anion is bis(trifluoromethanesulfonyl)imide (TFSI − ).By collaborating with ILs, sulfur polymers can acquire more distinctive properties like conductivity, [17] especially the solubility in water. [16]oreover, ILs and their polymeric form, poly(ionic liquid)s (PILs), are versatile materials widely applied in various fields such as CO 2 capture, [13] catalysis, [14] oil/water separation, [15] Scheme 1.General reaction of elemental sulfur with AVImCl.
Herein, we report the preparation of ionic liquid-containing sulfur polymers S-AVImCl, in which super hydrophilic 1-allyl-3-vinylimidazolium chloride (AVImCl) was combined with elemental sulfur and subjected to inverse vulcanization.The obtained sulfur polymer exhibited improved hydrophilicity and water solubility.The water solubility enables S-AVImCl to fully bind with mercury in water, rather than being limited to surface interactions compared with traditional sulfur polymers.After mercury uptake, the polymer was precipitated from water and can be easily removed by filtration.Moreover, the charged S-AVImCl was capable of breaking emulsions through an anion exchange process, wherein Cl − was exchanged with dodecylbenzenesulfonate (DBS − ) from the surfactant.Finally, the antibacterial activity of S-AVImCl against S. aureus was evaluated, and the results demonstrated its excellent antibacterial efficacy.

Synthesis and Characterizations of Polymers S-AVImCl
Polymers S-AVImCl were synthesized under different synthesis conditions following inverse vulcanization methods (Table S1, Supporting Information), [4] as schematically illustrated in Scheme 1. See the Supporting Information for more details.The reaction progress is shown in Figure S1 (Supporting Information), and the obtained polymers are brownish-black.Polymers were named xS-AVImCl-yr-zc, where x, y, and z represent the ratio of sulfur, reaction temperature, and curing temperature, respectively.Note that the standardized inverse vulcanization is to add comonomers to molten sufur (two-step procedure), while in this work, elemental sulfur and comonomer AVImCl were combined directly (one-step procedure) because sulfur is fully miscible with AVImCl as soon as it melts, which enables thiyl radicals to initiate the polymerization immediately. [23]As a control experiment, pure AVImCl was heated to equivalent conditions, but showed negligible reaction in the absence of sulfur, as evidenced by the existence of protons at the C═C bond positions of AVImCl (Figure S2, Supporting Information).
The structures of as-prepared S-AVImCl were characterized by Fourier-transform infrared (FTIR) spectra (Figure S3, Supporting Information).For polymers S-AVImCl-135r-135c, S-AVImCl-160r-160c, and S-AVImCl-160r-140c, the peaks attributed to alkene C═C stretching vibrations at 1649 cm −1 in AVImCl disappeared, suggesting the complete consumption of C═C bonds.However, signals of C═C bonds were still observed in polymer S-AVImCl-185r-140c, likely because not all AVImCl had access to sulfur before the formation of a viscous pre-polymer.In addition, new peaks belonging to C─S bonds at 830 cm −1 , together with peaks at 1173 cm −1 (C─N stretching vibrations in AVImCl) and 1548-1570 cm −1 (C = N stretching vibrations of imidazolium ring in AVImCl) were found in all polymers, indicative of successful polymerization of elemental sulfur and AVImCl. [24,25]igures 1 and S4 (Supporting Information) show the 1 H nuclear magnetic resonance (NMR) spectra of S-AVImCl.The group of peaks at 7.11, 5.78, and 5.37 ppm, and peaks (6.02 and 5.39 ppm) are assigned to the protons at vinyl and allyl in AVImCl, respectively.In the cases where the reaction and curing were carried out at 160 °C, these peaks completely disappeared, indicative of the thorough polymerization of elemental sulfur and AVImCl. 13C NMR spectrum of 50S-AVImCl-160r-160c also evidences the full consumption of comonomer after polymerization (Figure S5, Supporting Information).In contrast, protons at C═C bonds were still observed within other polymers.The reaction temperature is too low (135 °C) to open the S 8 cycles or too high (185 °C) for S 8 to have access to comonomer before vitrification.Also, S 8 was not able to consume all C═C bonds of AVImCl when the curing temperature was either 135 or 140 °C.Additionally, the integral ratio of vinyl and allyl protons helped determine the reactivity of these two double bonds in AVImCl.From the spectra, the increase in the integral ratio shows allylic double bonds are consumed preferentially during polymerization, indicating allylic double bonds are relatively susceptible to sulfur radical attack.The formation of peaks at ≈4.31 and 1.54 ppm in all polymers were observed, ascribed to the protons in S─C─H and C─H bonds, demonstrating the polymerization of elemental sulfur and AVImCl. [3,26]HNS elemental analysis was performed (Table S2, Supporting Information), and we can see that polymers with predetermined 50 wt.%sulfur have the roughly equivalent composition of elements to the calculated values.As shown by powder Xray diffraction (PXRD) (Figure S6, Supporting Information), no peaks appear in the curves of 50S-AVImCl-160r-160c and 50S-AVImCl-160r-140c, showing the absence of detectable unreacted crystalline sulfur in these two polymers.The thermal properties of as-prepared S-AVImCl were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).TGA results (Figure S7, Supporting Information) illustrate that all polymers have good thermal stabilities as the T deg,5% are ≈195 °C.As examined in DSC curves in Figure S8 (Supporting Information), the glass transition temperatures (T g ) of polymers were found to decrease as a function of increased sulfur ratios, consistent with the trend for other reported comonomers (DCPD, ENB, etc.). [3,27]Polymer 50S-AVImCl-160r-140c has the highest T g (42.78 °C) compared with T g (−5.54 °C) of 50S-AVImCl-135r-135c, T g (3.30 °C) of 50S-AVImCl-160r-160c, and T g (−47.49°C) of 50S-AVImCl-185r-140c.
According to these characterizations, it is concluded that when the reaction and curing temperature are both 160 °C, no crystalline sulfur and unreacted AVImCl remain in the polymer S-AVImCl of 50 wt.%sulfur (a yield of 92.7%).Therefore, this is the optimum reaction condition for the synthesis of polymers S-AVImCl, and thus 50S-AVImCl-160r-160c was chosen as a model for the solubility study and the sequent application tests.For convenience, the following polymer S-AVImCl refers to 50S-AVImCl-160r-160c.

Solubility of Polymer S-AVImCl
AVImCl is super hydrophilic and completely water soluble, which is attributed to the hydrophilic halide anion and short carbon chains of imidazolium cation.Therefore, the introduction of AVImCl to sulfur polymers is fundamental to water solubility enhancement.Table S3 (Supporting Information) presents the water contact angles (WCAs) of S-AVImCl and other conventional sulfur polymers.It is shown that S-AVImCl is hydrophilic, and gives the lowest WCA (24.35°) compared to S-DVB (90.05°),S-DCPD (88.26°),S-DIB (83.46°), and S─Sunflower oil (112.15°),proving the valid regulation of AVImCl on the hydrophilicity of sulfur polymers.
Solubility tests of S-AVImCl in water and organic solvents were carried out (Figures 2a; S9 and S10, Supporting Information).S-AVImCl is able to partially dissolve in water (49.1%),tetrahydrofuran (THF) (19.8%), dimethyl formamide (DMF) (87.4%), and CHCl 3 (13.3%),while not significantly dissolving in toluene (0.9%).Of particular interest is that S-AVImCl is partially water-soluble, very rare for inverse vulcanized polymers.Comonomer AVImCl has dual vinyl groups and is supposed to work as a cross-linker, providing network junction points and endowing the sulfur polymer with cross-linked network structures.][30] However, Pyun and co-workers recently discovered an alternative polymerization mechanism for inverse vulcanization where the linear polytetrasulfides poly(S-r-DIB) with bis-thiocumyl units was generated. [31]In brief, this new mechanism proposes the formation of only one C─S bond per isopropenyl group in DIB, rather than two C─S bonds suggested by the previous mechanism.Moreover, hydrogen abstraction occurred during the preparation of poly(S-r-styrene), affording branched and terminal fragments in polymers. [32]][35] Consequently, in this case, the possibility of partial solubility has been put forward.Polymer S-AVImCl contains cross-linked, non-cross-linked sections (the linear, sulfur loops, and branched structures), and monomeric thiols (thiolated comonomers) (Figure S11, Supporting Information).The formation of terminal methyl (≈18 ppm) and methylene (≈48 ppm) groups in linear units was proved by distortionless enhancement by polarization transfer (DEPT) 135 and heteronuclear single quantum coherence (HSQC) NMR (Figure S12, Supporting Information).The insolubility is attributed to the cross-linked section, while the solubility is rationalized by the non-cross-linked section and thiols.Consequently, the dissolving behavior of S-AVImCl is assumed as follows.When immersed in water, the hydrophilic polymer permits water to enter the polymeric networks; polymer chains stretch and become loose subsequently due to the electrostatic repulsion between imidazolium cations on backbones; the non-cross-linked segments and thiols isolate from the networks and dissolve.Theoretically, increasing curing time might affect the degree of branching and sulfur loops, which should result changes to the solubility and T g .Therefore, S-AVImCl with different curing time were prepared.Figure S13 (Supporting Information) shows the integral of protons decreases as cure time increases because of the increased hydrogen abstraction and generation of H 2 S. All of the polymers are able to partially dissolve in water (Figure 2b) with the soluble fraction above 44%.However, there is no clear correlation between solubility and T g , implying the effect of curing on water solubility of S-AVImCl remains undetermined.For the gel permeation chromatography (GPC) results of each S-AVImCl, Figure 2c-e reveal the soluble S-AVImCl consists higher and lower molecular weight fractions.In the case where S-AVImCl was cured for 24 h, the Mw is 26,066 g mol −1 (PDI = 3.13) and 266 g mol −1 (PDI = 1.20), respectively, with the weight fraction ratio of 0.92:1.It is speculated that the high molecular weight polymers are attributed to the formation of non-cross-linked units, while the small molecules are thiols free from the polymeric backbone.
The soluble and insoluble part of S-AVImCl were collected and named S-AVImCl-sol and S-AVImCl-insol.CHNS (Table S4, Supporting Information) evidences that sulfur content of S-AVImClsol is 24.59 wt.% (calculated sulfur rank = 1.11), less than that of S-AVImCl-insol (77.26 wt.%, calculated sulfur rank = 6.11).The high AVImCl and low sulfur content of S-AVImCl-sol partly account for its hydrophilicity, compared with the insoluble part with a water contact angle of 85.09°(Table S3, Supporting Information).From the TGA and DSC results (Figure S14, Supporting Information), T deg,5% of soluble and insoluble S-AVImCl are 182 and 226 °C, and the T g of soluble and insoluble S-AVImCl are −42.73 and −21.97 °C, respectively.PXRD and DSC proved no crystalline sulfur remains in S-AVImCl.However, "dark sulfur", unreacted amorphous sulfur not stabilized within the polymeric structure, [7] was observed in S-AVImCl-sol and S-AVImClinsol using thin layer chromatography (Figure S15, Supporting Information).

Mercury Capture
Sulfur polymers have been shown to have potential applications as novel remediation materials for mercury-contaminated water streams. [36]Recently, two main strategies for the en-hancement in mercury adsorption by sulfur polymers have been developed: increasing the surface area by preparing sulfur polymers as porous materials, [37,38] fibers, [39] coatings, [2,40] and nanoparticles [41,42] ; on the other hand, improvement to the hydrophilicity by polymerization with hydrophilic comonomers, for example, 2-carboxyethyl acrylate (CEA), [43,44] or introducing polar groups by post-functionalization. [45] Polymerized with AVImCl, S-AVImCl shows superior water-wetting behavior, and its watersoluble part is able to bind mercury effectively due to the high availability of surface sites.Therefore, S-AVImCl-sol was used in the following mercury capture tests.
A series of static tests were conducted to evaluate the mercury uptake ability of S-AVImCl-sol.In the case where the concentration of original HgCl 2 aqueous solution was above 500 ppm, a brown precipitate S-AVImCl/Hg was generated once the polymer solution was added (Figure 3a).Of interest, the filtrate obtained from the 2000 ppm Hg 2+ test became clearer; however, traces of S-AVImCl/Hg which did not aggregate, or S-AVImCl-sol in the filtrate was detected with a concentration of 0.17 mg mL −1 by quantitative NMR analysis (Figure S16, Supporting Information).This remains a challenge to sequester polymers from solutions completely.Figure 3b shows the high affinity with a saturated uptake capacity of 436 mg g −1 and reveals a steep uptake at low concentrations as well.The comparison of S-AVImCl-sol to other mercury adsorbents is displayed in Table S5 (Supporting Information).The maximum mercury capacity is a crucial parameter for evaluating mercury absorbents.Nevertheless, in practical scenarios, these materials are unlikely to encounter the amounts and concentrations of Hg 2+ necessary to reach saturation capacities.As long as the materials possess a considerable capacity (e.g., over 100 mg g −1 ) and ideally exhibit sharp uptake at low concen-trations, they can be used effectively.In this case, S-AVImCl-sol is comparable to reported adsorbents (Table S5, Supporting Information).S-AVImCl-insol exhibited less than one-tenth the uptake capacity of S-AVImCl-sol because of the limited active binding sites exposed to Hg 2+ .
As recently reported by Chalker and co-workers, sodium chloride interferes with mercury sorption by decreasing the rate and the amount of mercury uptake. [8]The uptake kinetics of Hg 2+ (500 ppm) onto S-AVImCl-sol in DI water, simulated tap water (6.85 mm NaCl), and seawater (599 mM NaCl) were investigated (Figure 3c).S-AVImCl-sol showed an effective uptake of 190 mg g −1 (DI water) and 173 mg g −1 (tap water), corresponding to 90.43% and 85.01% removal of mercury.However, a reduction in uptake (111 mg g −1 ) and removal (55.12%) was observed in the case containing higher NaCl concentration, indicating the high level of NaCl dramatically inhibited the effectiveness of S-AVImCl-sol.One possible speculation is that NaCl blocks or competes for the active binding site of polymer to mercury, even though S-AVImCl-sol overwhelms the surface area limits.
The pH of solutions may affect the metal ion removal process, therefore, mercury solutions with adjusted pH were applied to assess the uptake performance of the polymer.As presented in Figure 4a, 90.83% of mercury is removed when the mercury solution is neutral.In comparison, at pH4 and pH10, there was a degree of attenuation in mercury binding, with 79.58% and 82.86% removal, respectively.The influence of pH can be explained as follows: in acidic solutions, the cationic polymeric backbone of S-AVImCl-sol are protonated by H + and become more positive charged, therefore preventing Hg 2+ from binding to the polymer [46] ; in alkaline solutions, hydroxide species such as Hg(OH) + and Hg(OH) 2 might break S─S bonds in polymers and cover the active binding site as well, causing a negative effect on mercury capture. [8,46]electivity tests were conducted to evaluate the affinity of S-AVImCl-sol for diverse heavy metal ions at low concentrations.As depicted in Figure 4b, S-AVImCl-sol is able to capture 88.92% of Hg 2+ and 62.73% of Au + , while it is almost ineffective in removing Mn 2+ , As 3+ , Co 2+ , Ni 2+ , and Cr 3+ ions.The difference in uptake can be interpreted by Pearson's hard-soft-acid-base (HSAB) principle, which states that sulfur acts as a "'soft"' Lewis base and tends to bind "'soft"' Lewis acids, in this case, mercury and gold. [41]he precipitate S-AVImCl/Hg from 2000 ppm Hg 2+ test was collected in order to identify the state of mercury onto polymers.Complexes S-AVImCl/Hg are irregular powders, compared with the viscous S-AVImCl-sol (Figure S17, Supporting Information).EDX maps evidence the removal of Hg 2+ by S-AVImCl-sol as mercury was observed on the surface of polymers.In addition, the atomic ratio of sulfur to mercury is ≈3:1, implying that three sulfur atoms bind to one mercury atom as ligands (Figures S18  and S19, Supporting Information).XPS was applied to analyze the elemental composition of S-AVImCl-sol before and after mercury capture (Figure 5).Compared with S-AVImCl-sol, new intense peaks of Hg 4p, 4d 3/2 , 4d 5/2 , 4f, and 5d were detected in S-AVImCl/Hg, indicative of the enrichment of Hg on the polymer surface and successful capture of Hg 2+ (Figure 5a).For S-AVImCl-sol, the high-resolution S 2p spectrum (Figure 5b) was fitted with four peaks at 164.3, 163.1, 162.5, and 161.4 eV, which arise from S─S and C─S bonds.After the capture of mercury, the signals of C─S bonds shifted to higher binding energy (from 162.5 to 163.1 eV for S 2P 1/2 , and from 161.4 to 161.9 eV for S 2P 3/2 ).This indicates the formation of coordinate bonds between C─S and Hg, in which sulfur offers electrons to mercury. [46,17]ith respect to S─S bonds, no significant signal shift was observed, implying that there is no detectible interaction between S─S groups and Hg.In addition, it has been reported that electronrich nitrogen can participate in the chelation of Hg. [46] However, in this case, the N1s signals of imidazolium rings barely shifted, indicating no significant interaction between nitrogen and mercury (Figure S20a, Supporting Information). [15]Further confir- mation of the structure of S-AVImCl/Hg was obtained by PXRD (Figure S20b, Supporting Information).The PXRD result shows that the precipitate is amorphous because there are no reflection peaks corresponding to the hexagonal (wurtzite structure) phase -HgS or the cubic (zincblende structure) phase -HgS. [47]he lack of detected crystallinity is consistent with the Hg being bound by the polymer, rather than crystallising with free sulfur.Compared with S-AVImCl-sol, S-AVImCl/Hg contains less moisture, as evidenced by the disappearance of broad peaks at 3400 cm −1 (-OH groups in water) in FTIR spectra (Figure S20c, Supporting Information).

Demulsification
In the case of geological oil reservoirs, it is estimated that twothirds of the original oil in place (OOIP) is trapped in the reservoir rock pores by capillary forces. [48]As one of the practical techniques of chemical-enhanced oil recovery (CEOR), surfactant flooding is applied for improving oil recovery. [49]By adding surfactants as flooding agents, the trapped oil tends to be stripped off the rock, emulsified into water phase, and then transported along with water in the form of oil-in-water (O/W) emulsions. [50]owever, the emulsion needs to be separated into water and oil phases before undergoing further refinement.In CEOR application, anionic surfactants, for example alkylbenzene sulfonates, are commonly deployed to stabilize emulsions by forming electrostatic layers at the interface of oil droplets.Correspondingly, the addition of cationic demulsifiers in emulsions, such as ILs and PILs, is helpful to reduce the electrostatic repulsion among droplets, and disturbs the stability of emulsions. [18,19,51,52]In this work, polymer S-AVImCl acquires positive charges offered by AVImCl, which enables it to have potential as a demulsifier to break emulsions.
In a demulsification study, a dodecane-in-water emulsion (50% v/v) was prepared as a model O/W emulsion, where sodium dodecylbenzenesulfonate (SDBS) was used as an anionic surfactant.As shown in hot/cold stage optical microscopy (Figure S21 and Movie S1, Supporting Information), the emulsion type is identified as O/W emulsion based on the phase transition sequence of water and dodecane caused by temperature change.The prepared emulsion remained stable after 7 days, with dodecane droplets evenly dispersed in water, measuring less than 30 μm in diameter (Figure 6a).After the addition of S-AVImClsol solution, the oil droplets began to coalesce, become bigger, and eventually formed a continuous oil phase above the water.A new precipitate S-AVImDBS was formed as the third phase in the middle of the dodecane and water.The demulsified dodecane and water were separated and collected (Figure 6b-d).The demulsification efficiency (vol %) was calculated as 98.7% and Figure 6e presents the demulsification results.It is evident that the presence of oil in water was significantly reduced, as only a few droplets were observed.These droplets grew larger but did not sufficiently coalesce to phase separation.Furthermore, some precipitate S-AVImDBS was trapped in the droplets, evidencing its affinity for oil rather than water after demulsification.
The precipitate S-AVImDBS was collected and characterized by FTIR (Figure S22, Supporting Information).The characteristic peaks at 1168 and 1031 cm −1 (SO 3 − group), 667 cm −1 (out-ofplane C-H bending vibrations of benzene), and 2922 cm −1 (C-H stretching vibrations of alkyl) were observed, [53,54] indicative of the presence of DBS − ions in the precipitate.The concentration of Na + in the purified water (37.5 ppm) was tested similarly to its original concentration in the emulsion (33 ppm), which means the Na + remained in the water phase instead of settling out with the precipitate.DBS − ions in the demulsified water were not detectable by 1 H NMR (Figure S23, Supporting Information), revealing the precipitate took all DBS − ions.These results reveal that the demulsification mechanism is anion exchange between S-AVImCl and SDBS.As illustrated in Figure 6f, the electric double layer formed by SDBS at the interface of oil droplets hinders the coalescence of droplets by providing electrostatic repulsion.After the addition of S-AVImCl solution, Cl − of S-AVImCl tends to combine with Na + of SDBS and dissolves in the water phase.Meanwhile, the cationic polymeric backbone is able to pair with DBS − anions, which reduces the electrostatic repulsion among droplets and thus breaks the emulsion.The new formed S-AVImDBS is hydrophobic and eventually precipitates as a third phase.
Additional proof of anion exchange was achieved by the comparison of demulsification of three emulsions stabilized by anionic (SDBS), cationic (hexadecyltrimethylammonium bromide, CTAB), and nonionic (Tween 80) surfactants, respectively.The demulsification results are shown in Figure S24 (Supporting Information).S-AVImCl exhibited a good demulsification effect in the SDBS emulsion; on the contrary, it fails to break CTAB and Tween 80 emulsions in which oil and water are still mixed.Consequently, an anion exchange process is operative during demulsification, wherein S-AVImCl-sol is capable of exchanging Cl − for DBS − .

Antibacterial Activity
Sulfur polymers have potential biomedical applications due to their inhibitory effect against bacterial pathogens. [55,56][22] Therefore, the combination of sulfur polymers and ILs appears to offer potential for bacterial growth inhibition.
To assess the antibacterial activity of S-AVImCl-sol, a disc diffusion assay was conducted against Gram-positive methicillinresistant Staphylococcus aureus (strain USA300) and Gramnegative Pseudomonas aeruginosa (strain PAO1).Antimicrobial susceptibility test discs were soaked with polymer solution and compared to control samples which were prepared by soaking discs with water.The loaded discs were placed on agar plates streaked with bacteria and incubated for 24 h.As shown in Figures 7a and S25 (Supporting Information), S-AVImCl-sol inhibits the growth of S. aureus effectively, but shows no activity against P. aeruginosa.The results coincide with reports that ILs have higher antibacterial activity against Gram-positive bacteria in comparison to Gram-negative bacteria. [57]Therefore, S-AVImCl-sol at a concentration of 5 mg mL −1 was tested over a period of 5 h against S. aureus in Luria Bertani (LB) medium within which bacteria grow exponentially (Figure 7b; Figure S26, Supporting Information).After 5 h, a 3.5 log (99.97%) reduction of viable cells in the presence of S-AVImCl-sol was achieved, compared to the untreated control.The results indicate that water-soluble S-AVImCl exhibits antibacterial efficacy, and could potentially perform as an antibacterial agent for water remediation.

Conclusion
Water-soluble IL-containing sulfur polymers, S-AVImCl, were successfully synthesized by inverse vulcanization using 1-allyl-3vinylimidazolium chloride and elemental sulfur.Optimizing the polymerization conditions gave full conversion and a sulfur polymer yield of 92.7%.Benefiting from the enhanced hydrophilicity, the polymer is able to dissolve in water, providing maximized contact with aqueous ions compared to conventional sulfur polymers with limited surface area.A competitive mercury capture performance of S-AVImCl was observed, showing a steep uptake at low concentration.After metal uptake, a coordination complex S-AVImCl/Hg was generated due to the formation of C─S-Hg bonds, which then precipitated from solution.Furthermore, the sulfur polymer exhibited effective demulsification with respect to anionic O/W emulsions, achieving an impressive efficiency of 98.7%.It was found that the demulsification mechanism was anion exchange between Cl − of the polymer and DBS − of the surfactant.After anion exchange, the polymer became hydrophobic and precipitated, forming a third phase between purified oil and water.Finally, the polymer performs well in inhibition against S. aureus.With the help of ILs, the wettability behavior of sulfur polymers is able to be regulated, and the consequent watersoluble polymer is versatile and holds significant potential in many aspects of water purification.In future studies, it is necessary to explore the potential of neutral or negatively charged comonomers for enhancing the water-solubility of sulfur polymers.For the potential of these materials for water purification to be realized by industrial application, future work would likely benefit from exploring alternative related structures to optimize performance, as well as considering routes to scale up the synthesis, minimize the cost, and the stability and full life cycle of the material after use.

Figure 1 .
Figure 1. 1 H NMR spectra of polymer 50S-AVImCl-160r-160c in D 2 O.The protons at C═C bonds in comonomer are labelled H 1,2 and H 7,8 .The integrations of H 1,2 and H 7,8 peaks are relative to the integration of H 4,5 peak in order to identify the unreacted AVImCl in polymers.

Figure 2 .
Figure 2. a) Photograph of S-AVImCl in water, THF, toluene, DMF, ad CHCl 3 (from left to right).b) The soluble fraction in water and T g of S-AVImCl, and c) GPC curves (water as eluent), and molecular weight and dispersity of d) peak 1 and e) peak 2 of S-AVImCl as a function of curing time.Peak 1 refers to the non-cross-linked polymers with high molecular weight, while peak 2 refers to small thiols free from the polymeric backbone.Error bars shown are standard deviation from three repeat measurements.

Figure 5 .
Figure 5. a) Full survey XPS and b) S2p spectra of S-AVImCl-sol and precipitate S-AVImCl/Hg.Of note, the polymer was synthesized in a glass vial, so trace Si signal at 100.9 eV in S-AVImCl-sol was observed.

Figure 6 .
Figure 6.a) Dodecane-in-water emulsion dyed red and its microscopy image.Demulsification results after adding S-AVImCl-sol solution into the emulsion b) immediately and c) for 24 h.The process of small oil droplets aggregating into large ones is clearly visible.d) Separated dodecane and water, and e) microscopy image of water containing a few oil droplets.f) Schematic illustration for demulsification mechanism using S-AVImCl-sol.The electrical double layer at the interface of oil droplets was formed by SDBS, with dodecylbenzenesulfonate (DBS − ) headgroups in blue and Na + ions in green.During the demulsification, the polymeric imidazolium cations in black combined with DBS − , leading the neutralization of charged droplets and dissolution of NaCl into water.

Figure 7 .
Figure 7. a) Photograph of LB agar plate streaked with S. aureus loaded with antimicrobial susceptibility test discs containing 1) S-AVImCl-sol solution (50 mg mL −1 ), 2) water, and 3) empty disc.The clear zone around disc shows inhibition of S. aureus growth.b) S. aureus growth in the presence of S-AVImCl-sol over 5 h.Error bars shown are standard deviation from three repeat measurements.