Crosslinkable and Self-Foaming Polysulfide Materials for Repairable

Subscriber access provided by University of Winnipeg Library

Article

Crosslinkable and Self-Foaming Polysulfide Materials for Repairable and Mercury Capture Applications Ho-Keng Lin, Yue-Sheng Lai, and Ying-Ling Liu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06815 • Publication Date (Web): 24 Jan 2019 Downloaded from http://pubs.acs.org on January 30, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Crosslinkable and Self-Foaming Polysulfide Materials for Repairable and Mercury Capture Applications Ho-Keng Lin, Yue-Sheng Lai, and Ying-Ling Liu* Department of Chemical Engineering, National Tsing Hua University, #101, Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan * Corresponding author. E-mail: [email protected] (Y.-L. Liu) KEYWORDS Polysulfide, Repairable, Mercury absorption, Meldrum’s acid

ABSTRACT: Inverse vulcanization involves reactions between elemental sulfur and unsaturated organic compounds to result in polysulfide materials. In this work, a Meldrum’s acid-containing styrene compound (MA-St) has been employed in the inverse vulcanization process for introduction of MA moieties to the corresponding polysulfide material (poly(S-MA-St)). Poly(SMA-St) possesses self-crosslinking ability based on the sequential MA thermolysis and ketene (generated with MA thermolysis) dimerization reactions. With employing CO2, evolved with MA thermolysis reaction, as a foaming agent, poly(S-MA-St) also exhibits self-foaming feature in the thermally crosslinking process. Moreover, crosslinked poly(S-MA-St) material shows

1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 28

repairable property based on the dynamic polysulfide chains. As a result, poly(S-MA-St) is an effective agent for imparting repairable property to other polymers. On the other hand, crosslinked and foamed poly(S-MA-St), which possesses polysulfide chains and rich oxygen atoms and porous structure, has demonstrated a mercury absorption capacity of 52.0±1.8 mg Hg/g sample. While 100 mg sample being applied to 10 mL HgCl2 aqueous solution of a concentration of 2240 ppb in 3 h, a high mercury removal efficiency of 96% has been recorded. This work has demonstrated a new class of functional polysulfide materials on the viewpoints of both synthetic chemistry and application targets.

INTRODUCTION Developments of chemical processes using waste materials as feedstocks to synthesize functional polymeric materials have made admirable gains and provided alternative synthesis routes beneficial to sustainable developments and environment-friendly issues.1-2 The “inverse vulcanization” process uses elemental sulfur as a feedstock for preparation of polysulfide materials is an attractive example among the studied cases.3 In the “inverse vulcanization” process, sulfur carries out ring-opening polymerization at temperatures above its floor temperature to generate polysulfide chains. The chain ends possess radicals toward reacting to unsaturated organic compounds (as crosslinkers) to result in polymeric materials possessing polysulfide segments. Both alkene and alkyne compounds have been used as the organic crosslinkers.1,4-6 As addition reaction of elemental sulfur to benzoxazine rings has also been reported,7 benzoxazine compounds are also suitable crosslinkers for elemental sulfur in “inverse vulcanization” process. Based on employing various organic chemicals as crosslinkers, the resulting high-sulfur-content materials have shown interesting properties, such as high

2


Page 3 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrochemical specific capacity,3,8,9 repairable ability,10-13 high refractive index11,14 and heavy metal capture capability,15-21 as well as application potentials for environmental protection (heavy metal remediation, oil spill remediation and hydrocarbon sorbent),13,20-23 thermal insulation,22 antibacterial surfaces,24 solide-electrolytes,25 photoactive materials,26 and encapsulation for controlled-release fertilizers.27 Moreover, the polysulfide segments of the materials from “inverse vulcanization” process could carry out reduction reactions with breaking the polysulfide linkages.3,14,19 Breaks of polysulfide linkages would generate sulfur radicals which could initiate polymerization of vinyl and allyl ethers for post-modification of the polysulfide materials.28 Nevertheless, the reactions are not suitable and convenient routes for chemical modifications of the polysulfide materials. Introduction of functional and reactive groups to the polysulfide materials for further chemical reactions, such as modification and crosslinking reaction, is attractive. Reactive polysulfide materials have been obtained with 4vinylbenzyl chloride as the reactant in “inverse vulcanization” process.29 Post-modification of polysulfide materials was carried out with quaternization of alkyl chloride group. In this work, reactive polysulfide materials possessing Meldrum’s acid (MA) groups for post-modification and crosslinking are reported. Mercury, due to its high toxicity, might cause serious environmental and health issues.30-32 To address the mercury pollution issue, reduction of mercury release/emission from human activities and industries32 as well as mercury removal/capture from the waste matrix have received much attention. The above-mentioned polysulfide materials have been applied to removal and capture of mercury ions.14-21 Moreover, the polysulfide materials still exhibit sufficient ability to remove mercury in various forms, including liquid mercury, gaseous mercury, organo-mercury substances, and humic matter-bonded mercury.20 Based on the ability to oxidize mercury metal

3



Page 4 of 28

to mercury ions (Hg2+), the polysulfide materials are used as reactive absorbents and in sensing application.15,20 Polysulfide materials based on low-cost industrial by-products, like limonene and dicyclopentadiene,14 are especially attractive to address the environmental and economic concerns of mass production for mercury captures. Polybenzoxazines, which possess rich nitrogen and oxygen atoms being capable of binding mercury ions, have also been introduced to polysulfide materials7,33 showing high efficiency in mercury absorption and removal.33 Porous polysulfide materials have been reported to increase the effective area for mercury capture. One example of porous polysulfide materials is nanofiber mats obtained with electrospinning process.16 In the electrospinning process, another polymer, like poly(methyl methacrylate), was utilized to provide sufficient mechanical strength to the nanofiber mats. Consequently, the polysulfide contents in the electrospun nanofibers were below about 66 wt%, so as to limit their mercury capture performance. Other approaches reported for fabrication of porous polysulfide materials included supercritical CO2 foaming and salt-template process.15,18 The capacity of mercury capture increased with increasing the effective areas of the porous materials. Nevertheless, these two methods involved harsh operation conditions and complicated preparation routes. Arslan and coworkers33 reported that the reverse vulcanization between S8 and an allyl-benzoxazine compound might result in porous products foamed with the released gaseous byproduct (H2S). Although the authors claimed that the self-foamed product could be potential for some applications, further studies have not been reported. Employing the toxic H2S gas as a foaming agent might cause safety issues. Hence, a convenient and simple approach for fabrication of porous polysulfide materials is still under investigation. This work aims to address the above-mentioned issues of the inverse vulcanization based polysulfide materials, including introduction of functional and reactive groups to the polysulfide

4


Page 5 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


materials, selection of suitable crosslinkers contributing to mercury absorption, and convenient approaches for preparation of porous polysulfide materials. A monostyrenic compound containing a MA group has been utilized as the crosslinker (MA-St) in the inverse vulcanization process. As Pyun et al.3,8 reported that inverse vulcanization of sulfur and styrene might involve some chain transfer reactions at the benzylic carbons, the prepared MA-St based polysulfide (poly(S-MA-St)) would possess a linear and branched structure rather than a network so as to retain its solution processability. MA could undergo thermolysis reaction to generate highly reactive ketene group with involves of CO2 and acetone.14 It has been widely demonstrated that the ketene groups are effective for further chemical reactions with nucleophiles and selfcycloaddition dimerization.34-42 Therefore, poly(S-MA-St) could be considered as a reactive and crosslinkable polymer based on the above-mentioned MA reactivity and ketene chemistry. On the other hand, the evolved CO2 within MA thermolysis reaction has been utilized in in situ generation of micro-cavity in the crosslinked MA polymers showing low dielectric constants for microelectronics43,44 and high gas permeability for gas separation.45 This work aims to explore the first example of utilization the evolved CO2 within the MA thermolysis reaction as a foaming agent for preparation of porous polysulfide materials. Based on the high oxygen content of MA group, integration of MA moieties to the polysulfide material might provide additional contribution to mercury capture. Based on the molecular designs, functional and high performance of polysulfide material has been explored (Figure 1). RESULTS AND DISCUSSION Preparation of polysulfide material from elemental sulfur and MA-St

5



MA-St

is

obtained

from

2,2’,5-trimethyl-1,3-dioxane-4,6-dione

Page 6 of 28

(MA-M)

and

chloromethylstyrene according to the reported method.34 MA-St shows a melting point at about 91 oC in differential scanning calorimetric (DSC) analysis and an exothermic peak at about 180

Figure 1. (a) Reaction route of Meldrum’s acid derivative (MA-St) with elemental sulfur for preparation of MA-containing polysulfide (poly(S-MA-St)) and the corresponding dense crosslinked polysulfide (CR-polysulfide) and foamed CR-polysulfide (CR-polysulfide-F); (b) Thermolysis reaction of Meldrum’s acid group with evolving CO2 and acetone molecules and the following dimerization reaction of ketene groups; (c) a plot illustrating the crosslinking reaction of poly(S-MA-St) through MA thermolysis and ketene dimerization reaction.

6


Page 7 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


o

C corresponding to consequent MA thermolysis reaction and ketene dimerization (Figure S1).

While elemental sulfur (S8) being added to MA-St (weight ratio: 1:1), the mixture exhibits an endothermic peak at about 172 oC corresponding to the addition reaction between sulfur and styrenic group of MA-St. This reaction results in chemical linkages between sulfur and MA-St to restrict the mobility of MA groups, consequently to increase the energy barrier for MA thermolysis reaction. Hence, the reaction temperature of MA thermolysis shifts to about 212 oC. The result suggests that MA groups would not react toward sulfur. Moreover, MA thermolysis reaction might not take place at the reaction temperature set for inverse vulcanization process (about 170 oC). The obtained product from the reaction between sulfur and MA-St might retain MA groups. Spectral characterization and thermal analysis results supporting to the conclusion are discussed below. S8 and MA-St in a weight ratio of 3:2 were mixed together. The mixture was reacted at 170 oC for 25 min to perform the ring-opening reaction of S8 and the addition reaction of sulfur radicals to the styrenic groups. After carrying out further sulfide exchange reaction at 120 oC for 15 h, the product of poly(S-MA-St) was obtained (Figure 1).19 Reaction of S8 and MA-St at 170 oC for a longer time resulted in a gel product due to more complex reactions19 and possible MA ringopening reaction. Poly(S-MA-St) has been characterized with Fourier transform infrared spectroscopy (FTIR, Figure 2a). Compared to the FTIR spectrum recorded on MA-St, poly(SMA-St) shows a significant decrease in the intensity of the absorption peak at 1630 cm−1, which is associated with the absorption of C=C linkage of styrene group. The result indicates the consumption of C=C groups in the inverse vulcanization reaction between S8 and the styrene groups of MA-St. Poly(S-MA-St) still demonstrates the characteristic absorption peaks of MA group at 1051 cm−1 (C-O), 1774 cm−1 and 1778 cm−1 (C=O), indicating that MA groups did not

7



Page 8 of 28

involve in the inverse vulcanization reactions. The 1H-NMR spectra of MA-St and poly(S-MASt) are shown in Figure 2b. Poly(S-MA-St) exhibits decreases in the peak intensities of ArC=CH2 (δ = 5.2 ppm and δ = 5.7 ppm) and Ar-CH=C (δ = 6.65 ppm), supporting to occurrence of the reaction between sulfur radicals and styrenic groups of MA-St. Addition of sulfur

8


Page 9 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) FTIR and (b) 1H NMR spectra of the crosslinker (MA-St) and the product (poly(SMA-St)) of the S8/MA-St inverse vulcanization process. The FTIR spectrum of the crosslinked poly(S-MA-St) (CR-polysulfide) is also included in (a).

segments to styrenic groups generates the chemical structure of -Sx-CH2-CH-Ph- which exhibits the resonance peaks at δ = 9.97 ppm and δ = 7.35 ppm. The polysulfide chains induce substantial deshielding effect contributing to peaks shifts toward downfield. These two peaks give a peak area ratio of 1/2 which is in good agreement with the chemical structure. With the resonance peak (δ = 3.28 ppm) of Ph-CH2-MA- as an internal standard, the conversion of the C=C bonds in the inverse vulcanization reaction is about 94 %. The residual styrenic group might react with ketene groups so as to involve in the crosslinking reaction of poly(S-MA-St).43 Although the reaction conversion could be increased to above 99% with prolonging the reaction time at 170 oC. a high risk of gelation should be considered. The resonance peaks corresponding to MA groups (δ = 0.94 ppm and δ = 1.47-1.75 ppm) still appear in the 1H NMR spectrum of poly(S-MA-St). This result supports to both that MA group did not react with sulfur radicals in the inverse vulcanization process and that poly(S-MA-St) still possess reactive MA groups for further reactions. It is noteworthy that polysulfide segments might bond to MA-St in various ways (different segments lengths and mono- and di-substituted) so as to result in the multiple peaks associated with the MA moieties. The reaction of sulfur to styrenic groups has been further examined with 13C NMR (see supporting information). The signals of styrenic groups at around δ = 114 ppm and δ = 137 ppm which are observed with MA-St, do not appear in the spectrum of poly(S-MA-St). The C-S bonds in poly(S-MA-St) demonstrates resonance peaks at around δ = 40 ppm and δ = 50 ppm.3 Compared to the polysulfide materials from the inverse vulcanization

9



Page 10 of 28

processes employing bifunctional crosslinkers, MA-St has only one unsaturate group to react with S8. Hence, poly(S-MA-St) could possess a linear and branched structure rather than a network structure. Consequently, poly(S-MA-St) shows a high solubility in toluene (> 22.0 wt%), tetrahydrofuran (> 22.0 wt%), chloroform (about 19.0 wt%), and 1-methyl-2-pyrrolidone (NMP, about 13.0 wt%). The good solubility in organic solvents of poly(S-MA-St) warrants its good processing property for further applications. The number averaged molecular weight and polydispersity index of poly(S-MA-St) measured with a gel permeation chromatography (GPC) is 2,350 g mol-1 and 1.48, respectively. Poly(S-MA-St) could carry out crosslinking reaction through MA thermolysis reaction and consequent dimerization of the ketene groups generated with MA thermolysis reaction.43 The reactions could be associated to the endothermic peaks in the DSC heating scanning thermogram of poly(S-MA-St). As a result, the endothermic peak disappears in the second heating scan on the same sample. Consequently, crosslinked poly(S-MA-St) (CR-polysulfide) has been prepared through a thermally curing process. The preparation yield of the CR-polysulfide, compared to the weights of the poly(S-MA-St) precursor, is about 85 wt%. This value is coincident to the theoretical value of 85.6 wt%. The FTIR spectrum recorded on the cured sample (CRpolysulfide) is included in Figure 2a. Occurrence of MA thermolysis reaction is supported with the decreases in the absorption peak intensity of C-C-(C=O) groups (1051 cm−1) and C=O groups (1774 cm−1 and 1778 cm−1). The appearance of the absorption peak at about 1811 cm-1 indicates the formation of cyclobutane-1,3-dione (CBD) groups generated with the ketene dimerization reaction. The cured sample exhibits very different thermal properties compared to the poly(SMA-St) precursor. The exothermic peak observed with poly(S-MA-St) in DSC measurement is not observed in the thermogram of CR-polysulfide, suggesting the high conversion of MA

10


Page 11 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


thermolysis/ketene dimerization reactions. On the other hand, both MA-St and poly(S-MA-St) show a weight loss starting at about 200 oC in thermogravimetric analysis (TGA) due to evolves of CO2 and acetone molecules in MA thermolysis reaction.21 The weight loss at 250-350 oC of poly(S-MA-St) might be attributed to the breaks down of polysulfide segments, as this stage of weight loss is not observed with MA-St. CR-polysulfide does not exhibit weight loss behavior associated with MA thermolysis reaction (Figure S2), indicating both the high conversion of MA thermolysis/ketene dimerization reaction of poly(S-MA-St) and the highly crosslinked structure of CR-polysufide. Consequently, CR-polysulfide loses its solubility in the solvents which poly(S-MA-St) is readily soluble in. A high gel fraction of 94% has been recorded with the insoluble weight fraction of CR-polysulfide in chloroform after a 24 h test. Repairable crosslinked polymers based on poly(S-MA-St) The repairable feature of polysulfide-possessing polymeric materials from inverse vulcanization has been widely reported.1,2,3,6 In this work, the repairable feature of the insoluble and infusible CR-polysulfide material has also been examined. Thin films of both poly(S-MA-St) and CR-polysulfide were slightly cut with a surgical blade. The SEM images shown in Figure 3 were manually taken at the same spot of each sample for comparison, as the utilized SEM was not equipped with a heating stage for online monitoring. Poly(S-MA-St) shows a well repairable behavior after a thermal treatment at 100 oC for 10 min (Figure 3). As poly(S-MA-St) does not possess a highly crosslinked network, the repairable behavior of poly(S-MA-St) might be majorly contributed from the high chain mobility of poly(S-MA-St) at relatively high temperatures. On the other hand, CR-polysulfide has highly crosslinked networks composed of both polysulfide chains and interchain CBD linkages formed with ketene dimerization reaction. CR-polysulfide requires a relatively high temperature and a long thermal treatment time to

11



Page 12 of 28

demonstrate a repairable behavior sufficiently. Thermal treatment would partially break down the S-S bonds in the networks of CR-polysulfide. The molecular chains consequently regain their mobility, so as to heal the cut-print of the sample with chain motion. The results indicate that polymeric materials containing polysulfide bonds made with inverse vulcanization exhibit repairable features even though the materials possessing additional crosslinked structures.

Figure 3. (a) Photographs of the polymer (poly(S-MA-St)) prepared from the inverse vulcanization process of S8 and MA-St and the crosslinked polysulfide material (CR-polysulfide)

12


Page 13 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


obtained from thermally crosslinking poly(S-MA-St) sample. These two samples are subjected to thermally-triggered repairing tests; (b) SEM micrographs tracing the morphology changes of the poly(S-MA-St) and CR-polysulfide samples in the repairing tests.

Not only acting as a precursor for preparation of self-crosslinked material, poly(S-MA-St) could also be utilized as a functional additive to introduce polysulfide chains to other polymers so as to impart repairable feature to the polymers. In this work, an organo-soluble polyimide (Matrimid® PI) is taken as the matrix for this test (Figure 4). Neat PI and poly(S-MA-St)modified PI samples (possessing 25 wt% poly(S-MA-St)) have been subjected to a thermal treatment. The added poly(S-MA-St) carries out MA-based crosslinked reaction in the modified PI film, as what discussed above for the curing reaction of poly(S-MA-St). The neat PI and CRpolysulfide-modified PI samples after thermal treatment were immersed NMP for 24 h. The neat PI sample was completely dissolved in NMP, and the CR-polysulfide-modified PI was not soluble in NMP. A high gel fraction above 99 wt% was recorded. The high gel fraction of the modified PI sample suggests that reactions between PI chains and poly(S-MA-St) might occur in the heating process. Sulfur radicals generated from the breaks down of polysulfide chains28 might react toward the Ph-C(=O)-Ph groups of the Matrimid® PI chains. Further examination is interested in to explore the chemistry and materials between polysulfide and ketone-containing polymers. The repairable property of the PI samples was examined with the same manner for CR-polysulfide. The CR-polysulfide-modified PI sample demonstrates a repairable ability, meanwhile no repairing behavior has been observed with the neat PI sample. The results indicate that the portion of CR-polysulfide contributes to the repairable property of the CR-polysulfide-

13



Page 14 of 28

modified PI sample. Poly(S-MA-St) could be an effective additive to endow repairable ability to high performance polymers.

Figure 4. (a) Chemical structures of the polyimide utilized in this work for repairable property evaluation; (b) SEM micrographs tracing the morphology changes of the neat polyimide and poly(S-MA-St)-modified polyimide sample in the repairing tests.

Self-foaming feature of poly(S-MA-St)

14


Page 15 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As what discussed above and reported in the literature,34-44 thermolysis of MA moieties generates highly reactive ketene groups for further addition reactions with evolves of CO2 and acetone molecules. The reaction routes have been applied to preparation of a new class of thermosetting resins.36,37 In this work, we explore the first example of utilization of the evolved CO2 as the gas source for self-foaming MA-based crosslinked resins. The self-foaming feature of poly(S-MA-St) has been demonstrated. To carry out the in situ crosslinking and foaming reaction, a poly(S-MA-St) sample has been heated at 200 oC for 1 h to result in the crosslinked polysulfide foam (coded as CR-polysulfide-F, Figure 5). The morphology of CR-polysulfide-F has been observed with a SEM. In addition to the large pores and voids, the surfaces of the pores still exhibit some small pores in sub-micrometer scale. The hierarchical structure of pores might attribute to its high surface area contributing to absorption application. Further investigation on the optimum condition for the self-foaming behavior of MA derivatives is interesting in future work. The concept of self-foaming crosslinked polysulfide materials in the inverse vulcanization processes using the in situ generated gaseous H2S as the foaming agent was previously mentioned in literature.33 In the previous work,33 a benzoxazine derivative was utilized as the crosslinker in the reverse vulcanization process. The H2S byproduct formed from the thiolbenzoxazine addition reaction,7,33 As the system of this work does not contain benzoxazine compounds, H2S byproduct might not be produced in the reaction between sulfur and MA-St as well as in the crosslinking process of poly(S-MA-St). To verify this point, the gaseous streams containing the byproducts generated with the inverse vulcanization process of sulfur and MA-St as well as the thermally crosslinking process of poly(S-MA-St) were applied to a lead(II) acetate

15



Page 16 of 28

testing paper to probe the presence of H2S.7,43 As a negative result was observed, the reaction systems did not generate H2S byproduct.

Figure 5. (a) Photographs showing the in situ crosslinking and self-foaming feature of poly(SMA-St) for preparation of the foamed crosslinked sample of CR-polysulfide-F; (b) SEM micrographs of CR-polysulfide-F in various magnification.

16


Page 17 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Removal of mercury with absorption The foamed and crosslinked polysulfide sample (CR-polysulfide-F) has been applied to mercury absorption tests based on its high sulfur content, rich oxygen atoms, and porous structure. The first test has been carried out according to the method reported by Chalker’s group.15 About 300 mg of absorption material was prepared in an aluminum foil plate (area: 21 cm2) with the thermal process mentioned above. The absorption test was carried out with a 10 mL of HgCl2 aqueous solution (about 2.0 ppm) in 24 h. The Hg2+ concentration of the remained solution within S8 absorption test is about 690 ppb, which corresponds to an Hg2+-removal ability of 66 %. The Hg2+ concentration of the after-test solutions with poly(S-MA-St) and CRpolysulfide-F is 61 and 63 ppb, respectively. The low Hg2+ concentrations of the remained solutions support to the high mercury removal ability (about 96%) of both samples (Figure 6). Poly(S-MA-St) and CR-polysulfide-F have relatively low sulfur contents compared to S8. Nevertheless, these two samples show relatively high mercury removal ability which could be attributed to their carbonyl groups providing additional binding ability to mercury ions. As the sulfur-limonene polysulfide material was reported to exhibit a 55% of mercury removal ability,15 the high mercury removal ability of poly(S-MA-St) and CR-polysulfide-F samples is highly impressive. The mercury absorption capacities of the prepared polysulfide materials were also measured with the method reported with Hasell’s group on foamed samples.16 100 mg sample was put in 5 mL of HgCl2 aqueous solution (2240 ppb). After a 3 h test with stirring, the Hg2+ concentration of the solution tested with S8, poly(S-MA-St) and CR-polysulfide-F was 990, 690, and 530 ppb,

17



Page 18 of 28

respectively. The mercury removal ability of S8, poly(S-MA-St) and CR-polysulfide-F in this test is 55%, 69%, and 76%, respectively. Both poly(S-MA-St) and CR-polysulfide-F still showed

Figure 6. Photographs of (a) elemental sulfur, (b) poly(S-MA-St), and (c) CR-polysulfide-F samples subjected to mercury absorption tests based on the method reported with Chalker’s group;15 (d) Mercury removal efficiency of the three samples in the mercury absorption tests.

relatively high mercury absorption capacities compared to S8. Nevertheless, a 96% of mercury removal ability was reported to the sulfur-1,3-diisopropenylbenzene polysulfide foam made with a supercritical CO2 foaming process.16 To address this issue, the mercury absorption capacity of the samples at equilibrium conditions were measured. The non-foamed crosslinked CR-

18


Page 19 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


polysulfide sample shows a mercury absorption capacity of 50.5±0.3 mg Hg/g sample, which is comparable to the value (52.0±1.8 mg Hg/g sample) recorded on CR-polysulfide-F. The foam structure of CR-polysulfide-F sample does not contribute much to mercury absorption in this preliminary study. As the mercury absorption ability has been demonstrated to be highly dependent on the foaming conditions and the corresponding porous structures of the foamed products,16,19 optimizing the in situ crosslinking and self-foaming conditions of poly(S-MA-St) might be done in future work to further enhance the mercury removal ability of the reported CRpolysulfide-F materials. EXPERIMENTAL Materials Sulfur (sublimed power, 99.5%, Alfa Aesar), MA-M (2,2,5-Trimethyl-1,3-dioxane-4,6-dione, 97%, Aldrich), mercury(II) chloride (HgCl2, ≥99.5%, Sigma-Aldrich)), 4-vinyl benzylchloride (VBC, ≥95.0%, Aldrich), potassium carbonate (K2CO3, ≥99%, Sigma-Aldrich), N,Ndimethylforamide (DMF, Reagen Grade, TEDIA), NMP (reagent grade, ECHO) were used as received for chemical synthesis. Polyimide resin (PI, Matrimid®) was purchased from Alfa Aesar Chemical Company. Instrumental methods FTIR spectra were measured with a spectroscopy of PerkinElmer Spectrum Two FTIR. 1H-NMR spectra were recorded with Varian Unity Inova 500 NMR using DMSO-d6 as a solvent. A GPC composed with a Waters 1515 isocratic pump, a Waters 2414 refractive index detector, a series column of Waters styragel HR4/HR3 and Shodex KF-802, and a THF mobile phase (flow rate:

19



Page 20 of 28

1.0 mL min-1) was utilized for molecular weight measurements. DSC thermograms were recorded with a Thermal Analysis (TA) Instruments (Q20 DSC) at a heating rate of 10 oC min-1 under nitrogen atmosphere. TGA measurements were performed on a TA Instruments Q50 TGA instrument at a heating rate of 10 oC min-1 under nitrogen atmosphere with a flow rate of 100 mL min-1. SEM images were recorded by Hitachi SU8010 field-emission SEM. Concentration of mercury(II) ion was determined with an Agilent 7500ce inductively coupled plasma-mass spectrometer (ICP-MS). Preparation of poly(S-MA-St) Sulfur (S8, 0.8 g, 3.13 mmol) and MA-St (1.2 g, 4.86 mmol) were charged into a 10 mL vial equipped with a magnetic stir bar. The mixture was heated at 170 oC for 25 min, and then subsequently poured into a silicone mold for post-reaction at 120 oC for 15 h. After being cooled to room temperature, a transparent red sample of poly(S-MA-St) was obtained. Preparation of crosslinked samples of dense CR-polysulfide and foamed CR-polysulfide (CR-polysulfide-F) A solution of poly(S-MA-St) in NMP (15 wt%) was poured into an aluminum foil plate and then applied to a heating process at 150 oC for 30 min, 180 oC for 30 min, and 200 oC for 1 h. The stepwise heating process was utilized to prevent formation of rough surface of the samples caused by the evolved CO2 and acetone molecules. A solid and transparent CR-polysulfide sample was obtained. On the other hand, powder poly(S-MA-St) was placed in an aluminum foil plate and then heated at 200 oC for 1 h to result in the product of foamed CR-polysulfide sample (CR-polysulfide-F).

20


Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Preparation of CR-polysulfide modified PI film Poly(S-MA-St) (0.25 g), PI (0.75 g), and NMP (5 mL) were put in a 25 mL glass vial with a magnetic stir bar. The homogenous solution was casted on a glass plate and then thermally treated in a vacuum oven at 80 oC for 12 h, 150 oC for 0.5 h, 180 oC for 0.5 h, and 200 oC for 1 h. A transparent and solid film of CR-polysulfide modified PI film was obtained. Mercury absorption and removal tests Two methods for mercury absorption and removal tests were utilized in this work. The first test was carried out with the method reported by Chalker’s group.15 About 300 mg of samples (S8 and poly(S-MA-St)) were put in aluminum foil plates (area: 21 cm2). Another sample of poly(S-MA-St) in the foil plate was subjected to the above-discussed self-foaming process to result in the CR-polysulfide-F sample in the plate. 10 mL of HgCl2 aqueous solution (about 2.0 ppm) was added to each of the sample plates. After standing for 24 h, the Hg2+ concentrations of the solutions after tests were determined with an ICP-MS. The second test was carried out according to the method reported with Hasell’s group.16 The absorption samples (100 mg) were soaked in 5 mL of aqueous HgCl2 (2240 ppb) solutions for 3 h. The remained mercury content in the solution was measured with an ICP-MS. Moreover, the absorption capacity of the tested sample was determined with a similar manner in which a 20 mL of HgCl2 solution (280 ppm) was used. The absorption capacity was obtained with the equilibrium concentration of the solution after absorption. CONCLUSIONS

21



Page 22 of 28

Integration of reactive MA groups to polysulfide materials has been achieved with employing a styrene-modified MA derivative (MA-St) and sulfur in inverse vulcanization process. The synthetic concept reveals a new class of reactive polysulfide materials for further chemical modification and self-crosslinking. Moreover, the CO2 molecules evolved from MA thermolysis reaction has been utilized as a foaming agent, so as to explore the concept of in situ crosslinking and self-foaming of MA-based resins. In addition to novelty of materials synthesis, the prepared poly(S-MA-St) material could be utilized as an additive for conventional polymers to effectively introduce polysulfide linkages to the polymers so as to impart repairable feature to the material. On the other hand, the high content of oxygen atoms of MA moieties provides additional binding positions to mercury ions so as to work together with polysulfide chains for mercury absorption and removal application. Integration with the self-foaming feature, the foamed and crosslinked polysulfide sample demonstrates high mercury removal ability. This work demonstrates an attractive green and sustainable chemistry from raw materials (elemental sulfur) to application target (mercury removal). ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge. Thermal analysis of the prepared materials, 13C NMR spectra, solubility tests, in situ crosslinking and foaming reaction, more tests on mercury absorption (PDF) AUTHOR INFORMATION Corresponding Author *Corresponding Author: E-mail: [email protected] (Y.-L. Liu)

22


Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Author Contributions The manuscript has been written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Financial supports on this work from The Ministry of Science and Technology, Taiwan (MOST 105-2221-E-007-138-MY3 and MOST 106-2221-E-007-098-MY3). REFERENCES (1) Worthington, M. J. H.; Kucera, R. L.; Chalker, J. M. Green chemistry and polymers made from sulfur. Green Chem. 2017, 19, 2748–2761. (2) Lim, J.; Pyun, J.; Char, K. Recent Approaches for the Direct Use of Elemental Sulfur in the Synthesis and Processing of Advanced Materials. Angew. Chem. Int. Ed. 2015, 54, 3249 3258. (3) Chung, W. J.; Griebel, J. J.; Kim, E. T.; Yoon, H.; Simmonds, A. G.; Ji, H. J.; Dirlam, P. T.; Glass, R. S.; Wie, J. J.; Nguyen, N. A.; Guralnick, B. W.; Park, J.; Somogyi, A.; Theato, P.; Mackay, M. E.; Sung, Y. E.; Char, K.; Pyun, J. The use of elemental sulfur as an alternative feedstock for polymeric materials. Nat. Chem. 2013, 5, 518 - 524. (4) Sun, Z.; Xiao, M.; Wang, S.; Han, D.; Song, S.; Chen, G.; Meng, Y. Sulfur-rich polymeric materials with semi-interpenetrating network structure as a novel lithium–sulfur cathode. J. Mater. Chem. A 2014, 2, 9280-9286. (5) Dirlam, P. T.; Simmonds, A. G.; Kleine, T. S.; Nguyen, Anderson, L. E.; Klever, A. O.; Florian, A.; Costanzo, P. J.; Theato, P.; Mackay, M. E.; Glass, R. S.; Char, K.; Pyun, J. Inverse vulcanization of elemental sulfur with 1,4-diphenylbutadiyne for cathode materials in Li-S batteries. RSC Adv. 2015, 5, 24718-24722. (6) Glass, R. S.; Char, K.; Pyun, J. From waste to valuable plastics–Discovery of new paradigms from well-studied systems with elemental sulfur. Phosphorus Sulfur Silicon Relat. Elem. 2017, 192, 157-161.

23



Page 24 of 28

(7) Lin, H. K.; Liu, Y. L. Sulfur radical transfer and coupling reaction to benzoxazine groups: a new reaction route for preparation of polymeric materials using elemental sulfur as a feedstock. Macromol. Rapid Commun. 2018, 39, 1700832 (6 pages). (8) Zhang, Y.; Griebel, J. J.; Dirlam, P. T.; Nguyen, N. A.; Glass, R. S.; Mackay, M. E.; Char, K.; Pyun, J. Inverse vulcanization of elemental sulfur and styrene for polymeric cathodes in Li-S batteries. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 107-116. (9) Dirlam, P. T.; Park, J.; Simmonds, A. G.; Domanik, K.; Arrington, C. B.; Schaefer, J. L.; Oleshko, V. P.; Kleine, T. S.; Char, K.; Glass, R. S.; Soles, C. L.; Kim, C.; Pinna, N.; Sung, Y.; Pyun, J. Elemental Sulfur and Molybdenum Disulfide Composites for Li-S Batteries with Long Cycle Life and High-Rate Capability. ACS Appl. Mater. Interfaces 2016, 8, 13437−13448. (10) Lin, H. K.; Liu, Y. L. Reactive hybrid of polyhedral oligomeric silsesquioxane (POSS) and sulfur as a building block for self-healing materials. Macromol. Rapid Commun. 2017, 38, 1700051. (11) Griebel, J. J.; Nguyen, N. A.; Namnabat, S.; Anderson, L. E.; Glass, R. S.; Norwood, R. A.; Mackay, M. E.; Char, K.; Pyun, J. Dynamic covalent polymers via inverse vulcanization of elemental sulfur for healable infrared optical materials. Acs. Macro. Lett. 2015, 4, 862-866. (12) Arslan, M.; Kiskan, B.; Yagci, Y. Recycling and self-Healing of polybenzoxazines with dynamic sulfide linkages. Sci. Reports 2017, 7, 5207 (11 pages). (13) Parker, D. J.; Chong, S. T.; Hasell, T. Sustainable inverse-vulcanised sulfur polymers. RSC Adv. 2018, 8, 27892-27899. (14) Kleine, T. S.; Nguyen, N. A.; Anderson, L. E.; Namnabat, S.; LaVilla, E. A.; Showghi, S. A.; Dirlam, P. T.; Arrington, C. B.; Manchester, M. S.; Schwiegerling, J.; Glass, R. S.; Char, K.; Norwood, R. A.; Mackay, M. E.; Pyun, J. High Refractive Index Copolymers with Improved Thermomechanical Properties via the Inverse Vulcanization of Sulfur and 1,3,5Triisopropenylbenzene. ACS Macro Lett. 2016, 5, 1152-1156. (15) Crockett, M. P.; Evans, A. M.; Worthington, M. J. H.; Albuquerque, I. S.; Slattery, A. D.; Gibson, C. T.; Campbell, J. A.; Lewis, D. A.; Bernardes, G. J. L.; Chalker, J. M. Sulfur Limonene Polysulfide: A Material Synthesized Entirely from Industrial ByProducts and Its Use in Removing Toxic Metals from Water and Soil. Angew. Chem. Int. Ed. 2016, 55, 1714−1718.

24


Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(16) Hasell, T.; Parker, D. J.; Jones, H. A.; McAllister, T.; Howdle, S. M. Porous inverse vulcanised polymers for mercury capture. Chem. Commun. 2016, 52, 5383 - 5386. (17) Thielke, M. W.; Bultema, L. A.; Brauer, D. D.; Richter, B.; Fischer M.; Theato, P. Rapid Mercury(II) Removal by Electrospun Sulfur Copolymers. Polymers, 2016, 8, 266. (18) Akay, S.; Kayan, B.; Kalderis, D.; Arslan, M.; Yagci, Y.; Kiskan, B. Poly(benzoxazineco sulfur): An efficient sorbent for mercury removal from aqueous solution. J. Appl. Polym. Sci. 2017, 45306. (19) Parker, D. J.; Jones, H. A.; Petcher, S.; Cervini, L.; Griffin, J. M.; Akhtar, R.; Hasell, T. Low cost and renewable sulfur-polymers by inverse vulcanisation, and their potential for mercury capture. J. Mater. Chem. A 2017, 5, 11682-11692. (20) Worthington, M. J. H.; Kucera, R. L.; Albuquerque, I. S.; Gibson, C. T.; Sibley, A.; Slattery, A. D.; Campbell, J. A.; Alboaiji, S. F. K.; Muller, K. A.; Young, J.; Adamson, N.; Gascooke, J. R.; Jampaiah, D.; Sabri, Y. M.; Bhargava, S. K.; Ippolito, S. J.; Lewis, D. A.; Quinton, J. S.; Ellis, A. V.; Johs, A.; Bernardes, G. J. L.; Chalker, J. M. Laying waste to mercury: inexpensive sorbents made from sulfur and recycled cooking oils. Chem. Eur. J. 2017, 23, 16219-16230. (21) Abraham, A. M.; Kumar, S. V.; Alhassan, S. M. Porous sulphur copolymer for gas-phase mercury removal and thermal insulation. Chem. Eng. J. 2018, 332, 1-7. (22) Lundquist, N. A.; Worthington, M. J. H.; Adamson, N.; Gibson, C. T.; Johnston, M. R.; Ellisa, A. V.; Chalker, J. M. Polysulfides made from re-purposed waste are sustainable materials for removing iron from water. RSC Adv. 2018, 8, 1232-1236. (23) Worthington, M. J. H.; Shearer, C. J.; Esdaile, L. J.; Campbell, J. A.; Gibson, C. T.; Legg, S. K.; Yin, Y.; Lundquist, N. A.; Gascooke, J. R.; Albuquerque, I. S.; Shapter, J. G.; Andersson, G. G.; Lewis, D. A.; Bernardes, G. J. L.; Chalker, J. M. Sustainable polysulfides for oil spill remediation: repurposing industrial waste for environmental benefit. Adv. Sustainable Syst. 2018, 1800024 (7 pages). (24) Deng, Z.; Hoefling, A.; Théato, P.; K. Lienkamp, K. Surface properties and antimicrobial activity of poly(sulfurco1,3diisopropenylbenzene) copolymers. Macromol. Chem. Phys. 2018, 219, 1700497 (6 pages). (25) Liu, P.; Gardner, J. M.; Kloo, L. L. Solution processable, cross-linked sulfur polymers as solid electrolytes in dye-sensitized solar cells. Chem. Commun. 2015, 51, 14660-14662.

25



Page 26 of 28

(26) Zhuo, S.; Huang, Y.; Liu, C.; Wang, H.; Zhang, B. Sulfur copolymer nanowires with enhanced visible-light photoresponse. Chem. Commun. 2014, 50, 11208-11210. (27) Mann, M.; Kruger, J. E.; Andari, F.; McErlean, J.; Gascooke, J. R.; Smith, J. A.; Worthington, M. J. H.; McKinley, C. C. C.; Campbell, J. A.; Lewis, D. A.; Hasell, T.; Perkins, M. V.; Chalker, J. M. Sulfur polymer composites as controlled-release fertilisers. Org. Biomol. Chem. 2018. DOI: 10.1039/C8OB02130A. (28) Westerman, C. R.; Jenkins, C. L. Dynamic sulfur bonds initiate polymerization of vinyl and allyl ethers at mild temperatures. Macromolecules 2018, 51, 7233-7238. (29) Gomez, I.; De Añastro, A. F.; Leonet, O.; Blazquez, J. A.; Grande, H.-J.; Pyun, J.; Mecerreyes, D. Macromol. Rapid Commun. 2018, 39, 1800529 (6 pages). (30) Clarkson, T. W. Mercury: major issues in environmental health. Environ. Health Perspect. 1993, 100, 31-38. (31) Wang, Q.; Kim, D.; Dionysiou, D. D.; Sorial, G. A.; Timberlake, D. Sources and remediation for mercury contamination in aqueous systems – a literature review. Environ. Pollut. 2004, 131, 323-336. (32) Esdaile, L. J.; Chalker, J. M. The mercury problem in artisanal and small-scale gold mining. Chem. Eur. J. 2018, 24, 6905-6916. (33) Arslan, M.; Kiskan, B.; Yagci, Y. Combining elemental sulfur with polybenzoxazines via inverse vulcanization. Macromolecules 2016, 49, 767-773. (34) Leibfarth, F. A.; Kang, M.; Ham, M.; Kim, J.; Campos, L. M.; Gupta, N.; Moon, B.; Hawker, C. J. A Facile Route to KeteneFunctionalized Polymers for General Materials Applications. Nat. Chem. 2010, 2, 207−212. (35) Leibfarth, F. A.; Schneider, Y.; Lynd, N. A.; Schultz, A.; Moon, B.; Kramer, E. J.; Bazan, G. C.; Hawker, C. J. Ketene Functionalized Polyethylene: Control of Cross-Link Density and Material Properties. J. Am. Chem. Soc. 2010, 132, 14706−14709. (36) Miyamura, Y.; Park, C.; Kinbara, K.; Leibfarth, F. A.; Hawker, C. J.; Aida, T. Controlling Volume Shrinkage in Soft Lithography through Heat-Induced Cross-Linking of Patterned Nanofibers. J. Am. Chem. Soc. 2011, 133, 2840−2843. (37) Jung, H.; Leibfarth, F.A.; Woo, S.; Lee, S.; Kang, M.; Moon, B.; Hawker, C.J.; Bang, J. Efficient Surface Neutralization and Enhanced Substrate Adhesion through Ketene Mediated Crosslinking and Functionalization. Adv. Func. Mater. 2013, 23, 1597-1602.

26


Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Leibfarth, F. A.; Wolffs, M.; Campos, L. M.; Delany, K.; Treat, N.; Kade, M. J.; Moon, B.; Hawker, C. J. Low-Temperature Ketene Formation in Materials Chemistry through Molecular Engineering. Chem. Sci. 2012, 3, 766−771. (39) Gonza´lez, L.; Ramis, X.; Salla, J. M.; Mantecoń, A.; Serra, A. Reduction of the Shrinkage of Thermosets by the Cationic Curing of Mixtures of Diglycidyl Ether of Bisphenol A and 6,6-Dimethyl-(4,8-dioxaspiro[2.5]octane-5,7-dione). J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 6869–6879. (40) Garcıá, S. J.; Suay, J. Anticorrosive properties of an epoxy Meldrum acid cured system catalyzed by erbium III trifluromethanesulfonate. Prog. Org. Coat. 2006, 57, 319–331. (41) Garcıá, S. J.; Serra, A.; Suay, J. New Powder Coatings With Low Curing Temperature and Enhanced Mechanical Properties Obtained from DGEBA Epoxy Resins and Meldrum Acid Using Erbium Triflate as Curing Agent. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 2316–2327. (42) Gonza´lez, L.; Ferrando, F.; Ramis, X.; Salla, J. M.; Mantecoń, A.; Serra, A. Characterization of new reworkable thermosetting coatings obtained by cationic and anionic curing of DGEBA and some meldrum acid derivatives. Prog. Org. Coat. 2009, 65, 175–181. (43) Lin, L. K.; Hu, C. C.; Su, W. C.; Liu, Y. L. Thermosetting resins with high fractions of free volume and inherently low dielectric constants. Chem. Commun. 2015, 51, 12760 - 12763. (44) Chen, Y.; Lin, L. K.; Chiang, S. J.; Liu, Y. L. A Cocatalytic Effect between Meldrum's Acid and Benzoxazine Compounds in Preparation of High Performance Thermosetting Resins. Macromol. Rapid Commun. 2017, 38, 1600616 (5 pages). (45) Wu, C. Y.; Hu, C. C.; Lin, L. K.; Lai, J. Y.; Liu, Y. L. Liberation of small molecules in polyimide membrane formation: an effect on gas separation properties. J. Membr. Sci. 2016, 499, 20-27. (46) Bear, J. C.; McGettrick, J. D.; Parkin, I. P.; Dunnill, C. W.; Hasell, T. Porous carbons from inverse vulcanised polymers. Microporous and Mesoporous Mater. 2016, 232, 189.

27



Page 28 of 28

Self-foamed porous polysulfide materials for mercury capture/removal using abandoned elemental sulfur as a feedstock.

28


Crosslinkable and Self-Foaming Polysulfide Materials for Repairable

Recommend Documents