Sulfur-based hyper cross-linked polymers

Abstract

Various hyper cross-linked polymers (HCPs) based on tetrakis(thiylphenyl)methane were generated by sulphur-relevant chemistry. Disulfide and thioether connections were exploited as a direct route to produce three-dimensional polymers. HCPs based on a thio-ether connection were quantitatively generated in the presence of triethylamine and di-iodo derivatives by a nucleophilic substitution reaction. They exhibited a Brunauer–Emmett–Teller surface area of 177 m² g⁻¹ for N₂ adsorption at 77 K while disulfide HCPs directly generated by oxidation of the corresponding polythiophenol monomers did not exhibit any ability to store gaseous molecules. Thia-Michael addition between tetrakis(thiylphenyl)methane and N-aryl-bismaleimide derivatives was next realized and led to porous HCPs presenting a specific surface area up to 1675 m² g⁻¹ in sorption measurements using nitrogen gas at 77 K. These organic frameworks were insoluble in common organic solvents and showed a high thermal stability up to 500 °C.

---

Introduction

The recent development of three-dimensional polymers¹ offers new perspectives in gas storage, gas separation, heterogeneous catalysis, optoelectronics, energy conversion and storage as well as for superhydrophobic interfaces with the development of covalent organic frameworks (COFs),^2–7 conjugated microporous polymers,^8–13 polymers of intrinsic porosity^14–23 and hyper cross-linked polymers (HCPs).^24–31 Indeed, these three-dimensional polymers are mainly based on designed building blocks such as aromatic structures. After an appropriate condensation reaction between the aromatic monomers or with a linker, the macromolecular assemblies will be generated with discrete pores in their internal structure, displaying an interconnected networks of channels within gaseous molecules can be trapped.³² This research area has emerged ten years ago and is still in his early age. Tetrahedral monomers such as adamantane (Ad) or tetraphenylmethane (TPM) were largely employed for the generation of such macromolecular assemblies by means of boroxine rings,^2,6,33–36 imines,^37,38 triazines,^39–43 or C–C bonds.^9,27,44,45 In a recent communication, Yan and coll. have described a series of polyimides prepared by imidization reaction, which exhibited a surface area of 2346 m² g⁻¹.⁴⁶ Although COFs design research area is amplified in the last three years, the choice of synthetic routes are still limited and achievement of networks formation with new chemical linkage remains an important step as the limits of this chemistry is still not really well-known.⁴⁷ In our quest to develop novel porous materials,^27,48 we have recently reported the access in gram scale to a tetraphenylmethane core functionalized with four thiol functions 1 (Scheme 1).⁴⁹ In the present study, we wish to emphasize sulphur-chemistry for the generation of new HCPs, by exemplifying various types of chemical transformations starting from this monomer.

Scheme 1 Generation of HCPs based on tetrakis(thiylphenyl)-methane 1.

Results and discussion

Sulfur-based chemistry was not yet illustrated in the generation of covalently linked HCPs despite the tremendous growth of the field of nanoporous materials^32,50–55 during the last decade. We first envisioned a direct condensation of tetrakis(thiylphenyl)methane by an oxidation reaction to generate a disulfide connection. After optimization of the experimental conditions, HCP 2 was generated in a quantitative fashion under mild conditions in presence of hydrogen peroxide and a catalytic amount of sodium iodide at room temperature (Scheme 2a). The polymeric material was insoluble in all common solvents and showed a good thermal stability. Infrared spectroscopy, elemental analysis and solid-state NMR confirmed the assumed macromolecular structure. N₂ adsorption measurements performed at 77 K revealed a non-porous structure.⁴⁹ Aromatic polyfunctional linkers 3, 5 and 7 were next coupled with the tetrahedral monomer in the same conditions and led to the formation of HCPs 4, 6 and 8, respectively (Scheme 2b). As these polymers were insoluble in all the tested solvents, only solid-state analyses were considered. Infrared spectroscopy revealed no stretching band relative to free thiol functional group and elemental analysis was in good accordance with the theoretical values, suggesting the formation of the desired macromolecular structure. All three 3D-polymers 4, 6 and 8 exhibited a similar thermal behaviour. Indeed, a three-step decomposition was evidenced by TGA, with a first mass loss of 4.8%, 5.1% and 10.9%, respectively, occurring at 320 °C, followed by two other stages at 465 °C and 550 °C, respectively, leading to almost 24% mass loss for the three polymers. At 700 °C, the decomposition of the remaining carbonaceous scaffold began (see ESI†). The adsorption properties of these HCPs were determined at 77 K with nitrogen and revealed no ability to store gaseous molecules. Despite the aromatic nature of the reaction components, one can assumed that the disulfide connection is not appropriate for the generation of porous HCPs in the tested conditions. As the disulfide connection is known to be easily cleaved by appropriate chemical reagents such as disulfide derivatives or water-soluble phosphine, HCPs 2, 4, 6 and 8 were subjected to such depolymerisation conditions and the corresponding monomers were quantitatively recovered in presence of DTT⁵⁶ in 20 hours in slightly basic buffered solution or with TCEP⁵⁷ in 3 days at physiological pH, illustrating the reversible character of these new disulfide-based HCPs. Knowing that, the three-step decomposition profile showed by TGA could be interpreted as an in situ thermally induced disulfide exchange between the polymeric chains of the disulfide HCPs but no further supporting evidence corroborating such a phenomenon was ascertained.

Scheme 2 Generation of disulfide HCPs.

The nucleophilic properties of the reactive thiophenol functions were next submitted to nucleophilic substitutions with dihalide aromatic or aliphatic building blocks (Scheme 3). The reaction conditions were optimized for diiodomethane in polar aprotic solvents such as THF and 1,4-dioxane (Table 1, entries 1–3). The absence of a base such as triethylamine was prejudicial for the outcome of the reaction (entry 1). Indeed, in presence of triethylamine in THF, 73% of material was recovered after several days of reaction at room temperature (entry 2). Changing the solvent to 1,4-dioxane allowed the formation in quantitative yield of an insoluble material 9, which was subjected to further analyses.

Scheme 3 Generation of thioether-derived HCPs.

Table 1 Optimization of generation of HCPs 9–10

Entry	Linker	HCPs	Reaction conditions	Yield (%)	S^a
a S means specific surface area – Brunauer–Emmett–Teller method – and is calculated over the relative pressure range P/P0 = 0.05–0.3. Specific surface area is expressed in m^2 g^−1.
1	CH2I2	9	THF, r.t., 48 h	Traces	n.d.
2	CH2I2	9	NEt3, THF, r.t., 7 days	73%	15
3	CH2I2	9	NEt3, 1,4-dioxane, 100 °C, 7 days	Quant	177
4		10	NEt3, THF, 40 °C, 48 h	Quant	5
5		10	NEt3, 1,4-dioxane, 100 °C, 48 h	Traces	n.d.
6		10	THF, MeOH, NaOH, 60 °C, 5 days	Traces	n.d.
7		—	NEt3, THF, 40 °C, 48 h	Traces	n.d.

---

Infrared spectroscopy revealed the disappearance of the stretching band relative to the free thiol functional group. Elemental analysis fitted with the theoretical values. ¹³CP/MAS solid-state NMR showed the presence of broad peaks, inherent to a polymeric structure, in the aromatic (around 135–150 ppm) and aliphatic (14.5 ppm) domain that confirmed the assumed structure (Fig. 1). DSC revealed a high thermal stability up to 250 °C probably due to the cross-linked structure (see ESI†). The generated polymers were subjected to N₂ adsorption measurements at 77 K and exhibited a maximal specific surface area of 177 m² g⁻¹ for HCP 9 bearing a methylene junction (Fig. 2) with type-IV isotherm according to IUPAC classification.⁵⁸ The fast gas uptake at low pressure (0–0.1 bar) indicated a permanent microporous structure (pores size > 2 nm), and hysteresis loop in the desorption isotherm revealed a mesoporous character (mesopores 2–50 nm). The pore size distribution obtained with the Horváth–Kawazoe model⁵⁹ during the adsorption phase indicated a maximum pore diameter of 2 nm (see ESI†). Although these data could appear as encouraging results, no higher value of specific surface area was obtained, not even by decreasing the concentration of monomers to slow down the kinetics of the substitution reaction.

Fig. 1 Solid-state ¹³C CP/MAS NMR of monomer 1 and HCP 9.

Fig. 2 The 77 K N₂-adsorption isotherms of HCPs 9 (green, S = 15 m² g⁻¹; red, S = 177 m² g⁻¹ and 10 blue).

Bis-haloxylene derivatives such as 1,4-bis-bromomethyl-benzene or 1,4-bis-iodomethylbenzene were also explored as potential linkers. Despite the increased rigidity imposed by their aromatic structure, none of these linkers led to polymeric materials in the previously optimized reaction conditions (Table 2, entries 4–7 and Fig. 2).

Table 2 Generation of model compounds and HCPs 16, 18 and 20 via thia-Michael addition

Generation of model compounds
Entry	Product	Additive	Solvent	T	Time	Yield
1	13	NEt3	Toluene	r.t.	16 h	87
2	14	NEt3	Toluene	r.t.	16 h	66
3	13	AcOH	DMF	r.t.	16 h	82
4	13	AcOH	DMAc	r.t.	16 h	71
5	13	AcOH	NMP	r.t.	16 h	76

---

HCPs formation
Entry	Linker	HCPs	Reaction conditions		Yield
			Solvent	Additive
6	15	16	DMAc	NEt3	Traces
7	15	16	DMAc	AcOH	36
8	15	16	NMP	NEt3	Traces
9	15	16	NMP	AcOH	38
10	15	16	DMF	NEt3	Traces
11	15	16	DMF	AcOH	39

---

Another condensation reaction tested is the 1,4-thia-Michael addition to α,β-unsaturated ketone.⁶⁰ Our strategy included in a first approach the optimization of the reaction conditions on model compounds (Scheme 4a). As Michael acceptor, maleimide 13 was selected. Indeed, this structural moiety can be easily incorporated into a di-functionalized compound⁶¹ that would be used as a linker for the generation of the desired networks. Furthermore the high electrophilic character of the double bond due to the two adjacent carbonyl functions should increase the efficiency of the reaction.

Scheme 4 Generation of HCPs 16, 18 and 20 by thia-Michael addition.

The use of triethylamine enhanced the nucleophilic character of the thiol and allowed quantitative addition on the maleimide in the case of p-thiocresol 12 (Scheme 4a, Table 2, entry 1). A reasonable yield was also obtained for the reaction between tetrakis(thiylphenyl)methane 1 with maleimide 11 to generate the fourfold-functionalized TPM 14 (Scheme 4b, Table 2, entry 2). As suitable reaction conditions were identified with the model compounds for the planned reaction, investigation of network generation begun. Strong polar media were necessary to achieve the Michael addition in high rate and ideal solvents were found as dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) and dimethylformamide (DMF) (Table 2, entries 6, 8 and 10), nevertheless the relevant HCPs were formed with modest yield only. Prolonging the reaction time or raising the temperature did not improve the yield. Polymerization of bismaleimide 15 with various diamines by Michael addition were previously reported by Sava et al. in NMP.⁶⁰ In this strongly polar aprotic solvent, anionic polymerization was detected as an important competing side reaction to give polymaleimides. This difficulty can be circumvented by protonation of the anionic species by addition of a small amount of acetic acid or in presence of a protic solvent like m-cresol in parallel with a catalytic amount of tertiary amine as base. Addition of discrete p-thiocresol 12 on maleimide in acidified strong polar solvents was therefore realized and provided the desired product in each case without any side product (Table 2, entries 3–5). Established conditions on model compounds were consequently tested to generate networks from N-arylbismaleimide 15 and tetrakis(thiylphenyl)methane 1 (Scheme 3c). Reactions were performed with a small amount of acetic acid in polar media (Table 2, entries 7, 9 and 11) to generate 3D-polymer 16. After several washing steps, NMR analysis of the filtrates did not reveal impurities anymore for networks synthesized in acidified NMP, DMAc and DMF. The material generated in the presence of triethylamine in anhydrous conditions (Table 2, entries 6, 8, 10) was dissolved during the washing procedures, probably due to a higher rate of competing anionic polymerization leading to soluble products.

All the polymeric assemblies were insoluble in common solvents and disappearance of the stretching band relative to the thiol function was confirmed by infrared spectroscopy while stretching bands relative to carbonyl groups were detected. Elemental analysis was in moderate accordance with the theoretical values but ¹³C CP/MAS NMR corroborated the assumed structure (Fig. 3). Indeed, broad peaks at 170 ppm were assigned to the phenyl rings of TPM and bismaleimide, while low magnetic field signals appeared corresponding to the carbonyl groups (178 ppm) and signals at 40–58 ppm were relevant to the aliphatic carbons arisen from the addition of the thiol function on the C–C double bond of the native maleimide. DSC analyses were realized but no glass transition was detected for HCPs, due to the high degree of crosslinking. However N₂ adsorption–desorption measurements performed at 77 K revealed that HCP 16 generated in DMAc and in DMF presented a high porosity with a specific surface area of 1675 and 760 m² g⁻¹, respectively (Table 3), while the same network generated in NMP under identical conditions did not show any ability to store nitrogen. As shown in Fig. 4, type-III nitrogen gas adsorption isotherms were obtained, suggesting a mesoporous character for these networks with weak adsorbate–adsorbent interactions. At low pressure (0–0.1 bar), fast gas uptake demonstrated a permanent microporous architecture and the desorption phase indicated a mesoporous character as a large hysteresis loop was obtained. For calculation of the pores, the Horváth–Kawazoe model was used⁵⁹ and the specific surface areas were calculated by using the BET nitrogen adsorption method (Table 3). The pore size distribution obtained with the Cranston and Inkley model⁶² indicated a mesoporous character with pores diameter comprised between 1 and 15 or 11.6 nm for HCP 16 synthetized in DMAc or DMF, respectively. Problematically, yields were very low and increase in the amount of acetic acid led to better rate conversion but the generated networks did not exhibit similar specific surface area values anymore as they were found essentially non porous. Changing the nature of the bismaleimide linker to 17 or 19 did not enhance the adsorption properties of these networks although almost quantitative yields were obtained for their formation in presence of acetic acid (Table 3, entries 3–4). Even by realizing the thia-Michael addition at higher temperature e.g. 100 °C to increase the low solubility of the employed linkers and prolonging reaction time up to several days did not improve the gas storage properties of these HCPs (data not shown). This observation may arise from a too large degree of liberty of the macromolecular structure during its formation due to the increased length of the linker, which could lead to interpenetration of the generated channels.

Fig. 3 Solid-state ¹³C CP/MAS NMR of monomers 1, 15 and of HCP 16.

Table 3 Adsorption data of HCPs 16, 18 and 20

Entry	HCP	Reaction conditions		S^a	Total pore volume^b
		Solvent	AcOH (mL)
a Surface area calculated over the relative pressure range P/P0 = 0.05–0.3. Specific surface area is expressed in m^2 g^−1.b Total pore volume for P/P0 = 0.99 and is expressed in cm^3 g^−1.
1	16	DMAc	0.2	1675	0.2019
2	16	DMF	0.2	760	0.0968
3	16	NMP	0.2	—	—
4	18	DMF	2	—	—
5	20	DMF	2	—	—

---

Fig. 4 The 77 K N₂-adsorption isotherms of HCPs 16 synthetized in acidified DMAc (green), DMF (red) and NMP (blue).

Conclusions

In conclusion, we have reported applicable reaction conditions to build new HCPs based on a fourfold-functionalized sulfur-modified tetrakisphenylmethane core. Various characterization methods of the networks were applied and supported the assumed structure in all cases. The objective of the work presented here was to identify the suitability of sulfur-based chemistry as a new way to generate porous HCPs. Although optimization of reaction conditions were identified to prepare quantitatively the desired assemblies, moderate results were obtained in terms of N₂ adsorption properties while high thermal stability of these HCPs were proved by TGA. As HCPs are an emerging class of porous polymers and are currently synthesized via a few numbers of chemical reactions, the access and exploitation of new structures and properties are limited. Although the porosities presented in this article are not as high as for other HCPs, we do believe that this work will make an interesting contribution to the building of heteroatom-based HCPs and even COFs as crystallinity is not a prerequisite in the development of porous networks.

Experimental

Materials and methods

Solvents, reagents and chemicals were purchased from Sigma-Aldrich, ABCR, Alfa Aesar and Acros Organics. Tetrakis(thiylphenyl)methane (ref. 49) dithiol linkers 3, 5 and 7 (ref. 63) and N-arylbismaleimide linkers 15, 17 and 19 (ref. 60, 64 and 65) were obtained according to literature procedures. All reagents and solvents were used as received.

NMR. NMR spectra were recorded on a Bruker AM 300 (300 MHz) as solutions in CDCl₃. Chemical shifts were expressed in parts per million (ppm, δ) downfield from tetramethylsilane (TMS) and were referenced to CHCl₃ (7.26 ppm) as internal standard. The spectra were analysed according to first order. The solid-state NMR spectra were measured on a Bruker Avance 400 spectrometer operating at 100.6 MHz for ¹³C NMR. The ¹³C CP/MAS (Cross-Polarization with Magic Angle Spinning) experiments were carried out at MAS rates of 14 kHz using densely packed powders of the compounds in 4 mm ZrO₂ rotors. The ¹H π/2 pulse was 4 μs and decoupling was used during the acquisition. The Hartmann–Hahn condition was optimized with Adamantane at a rotational speed of 5 kHz. All spectra were measured using a contact time of 1.5 ms and a relaxation delay of 10.0 s, and 6000 FIDs were accumulated.

ATR-IR. IR spectra were recorded with a FT-IR Bruker IFS 88 spectrometer with OPUS software using the attenuated total reflection technique (ATR). The deposit of the absorption band was given in wave numbers ν in cm⁻¹. The forms and intensities of the bands were characterized as follows: vs = very strong 0–10% T, s = strong 11–40% T, m = medium 41–70% T, w = weak 71–90% T, vw = very weak, 91–100% T, br = broad.

Mass spectrometry. Electron impact mass spectrometry (EIMS) was performed by using a Finnigan MAT 90 (70 eV).

Elemental analysis. The EA measurements were performed on an Elementar vario MICRO device using a Sartorius M2P precision balance. The following abbreviations were used: anal. calc. = calculated data, found = measured data.

Thermal characterization. The dynamic differential scanning calorimetry (DSC) was measured on a METTLER Toledo DSC 30, in a sealed aluminium 40 μL pan under argon atmosphere, using a heat–cool–heat thermal cycle. A typical thermal cycle started by heating the sample from −50 to 250 °C at 10 °C min⁻¹, the sample was cooled at 20 °C min⁻¹ to reach −50 °C. The third step of the cycle was heating the sample from −50 °C to 250 °C at 10 °C min⁻¹. The obtained data was analysed electronically with the software program STAR ^eSW 8.10 and was plotted in a diagram. The enthalpy changing ΔH [mW] was plotted against the temperature (−50 to −250 °C) under the heating rate of 10 °C min⁻¹. Thermal gravimetric analysis (TGA) was performed on a Shimadzu TGA-50 Thermogravimetric Analyser, using a heating rate of 10 °C min⁻¹ from room temperature to 1000 °C under N₂ atmosphere. Analysis of the thermal data was performed using the software program STAR ^eSW 8.10.

N₂ adsorption measurements. Gas adsorption isotherms were measured volumetrically using a surface analyser ThermoScientific Surfer Gas adsorption Porosimeter. A liquid nitrogen bath (77 K) was used and the N₂ gas used was UHP grade. For measurement of the specific surface areas (S_BET, m² g⁻¹) the BET method was applied. For all isotherms plots, closed circles are used for adsorption data points and open circles are used to indicate desorption data points. The pore size distribution was obtained with the Horváth–Kawazoe model (ref. 49) for the microporous HCPs or the Cranston and Inkley model (ref. 62) for the mesoporous HCPs.

Oxidative route – general protocol for the synthesis of 2, 4, 6 and 8

Tetrakis(thiylphenyl)methane 1 (0.100 g, 0.23 mmol, 1.0 equiv.) and thiolinker (0.46 mmol, 2 equiv. for the generation of HCP 2 and 4; 0.052 g, 0.30 mmol, 1.3 equiv. for the generation of HCP 6) was dissolved in ethyl acetate (20 mL) and NaI (0.3 mg, 0.002 mmol, 0.01 equiv.) was subsequently added with aq. 30% H₂O₂ (0.75 mL, 11.14 mmol, 6.0 equiv. per SH function). The mixture was stirred at room temperature for two hours. Saturated aqueous Na₂S₂O₃ (15 mL) was added, and the resulting solid was filtrated and extensively washed with water (30 mL), MeOH (30 mL), then with THF (30 mL), acetone (30 mL) and CH₂Cl₂ (50 mL). The resulting HCP was dried at 60 °C under vacuum during 24 h.

HCP 2. m = 0.096 g (97%). ¹³C CP/MAS NMR (100 MHz): δ = 68.1 (br, C_quart, C(Ar)₄), 137.0 (br, C_quart, CS, CH), 148.0 (br, C_quart, CC) ppm. IR (ATR): ν = 3073 (vw), 3020 (vw), 1586 (vw), 1561 (vw), 1482 (w), 1398 (w), 1307 (vw), 1271 (vw), 1239 (vw), 1191 (vw), 1101 (vw), 1081 (vw), 1012 (w), 951 (vw), 912 (vw), 809 (m), 760 (vw), 737 (vw), 695 (vw), 631 (vw) cm⁻¹. EA anal. calc. for (C₂₅H₁₆S₄ + Na): C 64.21, H 3.45, S 27.42; found C 64.48, H 3.61, S 27.18.

HCP 4. m = 0.155 g (96%). IR (ATR): ν = 3071 (vw), 3023 (vw), 1589 (vw), 1562 (vw), 1479 (w), 1399 (w), 1308 (vw), 1273 (vw), 1239 (vw), 1192 (vw), 1105 (vw), 1079 (vw), 1014 (w), 948 (vw), 914 (vw), 811 (m), 759 (vw), 738 (vw), 697 (vw), 629 (vw) cm⁻¹. EA anal. calc. for C₃₇H₂₄S₈: C 61.29, H 3.33, S 35.38; found C 61.07, H 3.48, S 35.45.

HCP 6. m = 0.193 g (99%). IR (ATR): ν = 3072 (vw), 3017 (vw), 1584 (vw), 1563 (vw), 1485 (w), 1397 (w), 1306 (vw), 1276 (vw), 1237 (vw), 1189 (vw), 1102 (vw), 1079 (vw), 1013 (w), 953 (vw), 913 (vw), 807 (m), 762 (vw), 736 (vw), 693 (vw), 633 (vw) cm⁻¹. EA anal. calc. for C₄₉H₃₂S₈: C 67.08, H 3.68, S 29.24; found C 67.22, H 3.47, S 27.31.

HCP 8. m = 0.145 g (96%). IR (ATR): ν = 3069 (vw), 3020 (vw), 1587 (vw), 1561 (vw), 1480 (w), 1396 (w), 1305 (vw), 1272 (vw), 1242 (vw), 1188 (vw), 1100 (vw), 1079 (vw), 1011 (w), 954 (vw), 909 (vw), 808 (m), 758 (vw), 735 (vw), 697 (vw), 632 (vw) cm⁻¹. EA anal. calc. for C₉₉H₆₀S₂₄: C 58.89, H 3.00, S 38.11; found C 58.81, H 3.05, S 38.14.

Nucleophilic substitution – generation of HCP 9

Tetrakis(thiylphenyl)methane (0.112 g, 0.25 mmol, 1.0 equiv.) was dissolved in abs. 1,4-dioxane (20 mL) under an inert atmosphere. Subsequently, triethylamine (0.21 mL, 6 equiv.) and diiodomethane (0.134 g, 0.50 mmol, 2.0 equiv.) was added under vigorous stirring. The mixture was stirred at 100 °C during 1 week. The resulting insoluble solid was filtrated and subsequently washed with THF (20 mL), acetone (20 mL) and CH₂Cl₂ (20 mL) and dried at 100 °C under vacuum during 24 hours to afford quantitatively the desired HCP (m = 0.123 g).

HCP 9. ¹³C CP/MAS NMR (100 MHz): δ = 150.1 (br, C_quart, CC), 136.1 (br, C_quart, CS, CH), 68.5 (br, C_quart, C(Ar)₄), 14.5 (br, CH₂) ppm. IR (ATR): ν = 3069 (vw), 3010 (w), 3025 (vw), 2970 (w), 2916 (w), 1586 (vw), 1561 (vw), 1482 (w), 1438 (s), 1398 (w), 1307 (vw), 1271 (vw), 1239 (vw), 1191 (vw), 1101 (vw), 1081 (vw), 1012 (w), 951 (vw), 912 (vw), 809 (m), 760 (vw), 737 (vw), 695 (vw), 631 (vw) cm⁻¹. EA anal. calc. for C₂₇H₂₀S₄: C 68.60, H 4.27, S 27.13; found C 68.26, H 4.40, S 27.34.

Generation of HCP 10

Tetrakis(thiylphenyl)methane (0.110 g, 0.25 mmol, 1.0 equiv.) was dissolved in abs. THF (20 mL) under an inert atmosphere. Subsequently, triethylamine (0.21 mL, 6 equiv.) and 1,4-bis-bromomethyl-benzene (0.129 g, 0.5 mmol, 2.0 equiv.) was added under vigorous stirring. The mixture was stirred at room temperature during 48 hours. The resulting insoluble solid was filtrated and subsequently washed with THF (20 mL), acetone (20 mL) and CH₂Cl₂ (20 mL) and dried at 100 °C under vacuum during 24 hours to afford 10 in a quantitative yield (m = 0.160 g).

HCP 10. ν = 3071 (vw), 3017 (vw), 3000 (w), 2951 (w), 2920 (w), 1586 (vw), 1561 (vw), 1482 (w), 1454 (m), 1398 (w), 1307 (vw), 1271 (vw), 1239 (vw), 1191 (vw), 1101 (vw), 1081 (vw), 1012 (w), 951 (vw), 912 (vw), 809 (m), 760 (vw), 737 (vw), 716 (vw), 695 (vw), 631 (vw) cm⁻¹. EA anal. calc. for C₄₁H₃₂S₄: C 75.42, H 4.94, S 19.64; found C 75.01, H 5.22, S 19.77.

Thia-Michael addition – generation of model compounds 13 and 14

3-(p-Tolylthio)pyrrolidine-2,5-dione 13. A solution consisting of maleimide 11 (0.129 g, 1.3 mmol, 1.1 equiv.), p-thiocresol 12 (0.150 g, 1.2 mmol, 1 equiv.) and acetic acid in polar solvent such as DMAc, DMF or NMP (10 mL) was allowed to stir at room temperature for 16 h. The crude mixture was poured in acidified water (15 mL) and dichloromethane (50 mL) was added. The mixture was separated and the organic phase was extracted with dichloromethane (2 × 25 mL). The organic phase was washed with H₂O (5 × 50 mL) and finally with saturated aqueous NaCl (50 mL), and dried over MgSO₄, filtered and evaporated to dryness to afford 3-(p-tolylthio)pyrrolidine-2,5-dione in 71% yield (0.188 g). ¹H NMR (300 MHz, CDCl₃): 7.63 (br, s, 1H) 7.42 (d, J = 8.1 Hz, 2H), 7.13 (d, J = 8.0 Hz, 2H), 4.01 (dd, J = 9.2, 4.4 Hz, 1H), 3.15 (dd, J = 18.9, 9.2 Hz, 1H), 2.74 (dd, J = 18.9, 4.3 Hz, 1H), 2.35 (s, 3H). ¹³C NMR (75 MHz, CDCl₃): 175.9, 174.7, 139.9, 134,9, 130.3, 126.3, 45.6, 37.01, 21.2 ppm. MS (EI): 221 [M⁺], 150 [M⁺ − C₂HO₂N], 123 [M⁺ − C₄H₄O₂N], 77 [M⁺ − C₅H₆O₂N]. ATR-IR: 3325, 2907, 1697, 1488, 1341, 1169, 950, 815, 760, 635, 553 cm⁻¹. EA anal. calc. for C₁₁H₁₁NO₂S: C 59.71, H 5.01, N 6.33, S 14.49; found: C 59.71, H 4.98, N 6.30, S 14.57.

3,3′,3′′,3′′′-[(Methanetetrayltetrakis(benzene-4,1-diyl))tetrakis(sulfane diyl)]tetrakis(pyrrolidine-2,5-dione) 14. Tetrakis(thiylphenyl)methane 1 (0.115 g, 0.26 mmol, 1 equiv.) was added to a solution of maleimide 11 (0.110 g, 1.04 mmol, 4.1 equiv.) and triethylamine (0.1 mL, 0.741 mmol, 2.8 equiv.) in toluene (10 mL) over a period of 30 minutes. The solution was diluted with toluene (20 mL) and stirred overnight at room temperature. The solvent was then evaporated and washed with dichloromethane (3 × 15 mL) to remove starting materials, affording 14 as a white solid (66%, 0.141 g). ¹H NMR (300 MHz, acetone-d₆): 7.49 (d, J = 8.6 Hz, 8H), 7.15 (d, J = 8.4 Hz, 8H), 4.35 (ddd, J = 9.1, 4.1, 1.0 Hz, 4H), 3.32 (dd, J = 18.5, 9.2 Hz, 4H), 2.65 (dd, J = 18.4, 4.1 Hz, 4H). ¹³C NMR (75 MHz, DMSO d₆): 177.2, 176.2, 145.0, 131.0, 130.9, 130.6, 44.2, 37.5 ppm. MS (FAB): 836 [M⁺]. ATR-IR: 3205, 3076, 1699, 1483, 1341, 1171, 949, 813, 795, 633, 549 cm⁻¹. EA anal. calc. for C₄₁H₃₂N₄O₈S₄: C 58.84, H 3.85, N 6.69, S 15.32; found: C 58.82, H 4.09, N 6.92, S 15.04.

Thia-Michael addition – general protocol for the synthesis of HCPs 16, 18 and 20

A solution consisting of N-arylbismaleimide (0.75 mmol, 2 equiv.), tetrakis(thiylphenyl)methane 1 (0.167 g, 0.37 mmol, 1 equiv.) and acetic acid in dry polar media (15 mL) was allowed to stir at room temperature for 2 days in a sealed tube. The crude mixture was poured in acidified methanol under vigorous stirring. The resulting solid was filtered and extensively washed with THF, methanol, acetone and dichloromethane followed by a purification step with Soxhlet extraction with methanol during 16 h, acetone (16 h) and dichloromethane (16 h) to afford the resulting HCP.

HCP 16. HCP 16 generated with 0.2 mL of AcOH. m = 0.132 g (36%). ¹³C CP/MAS NMR (100 MHz): δ = 178.0 (br, C_quart, CO), 151.6 (br, C_quart, CC), 138.3 (br, C_quart, CS, CH), 136.4 (br, C_quart, CS, CH), 68.7 (br, C_quart, C(Ar)₄), 48.4 (br, CS), 40.4 (br, CH₂) ppm. ATR-IR (ATR): ν = 1783 (vs), 1710 (vw), 1499 (vs), 1360 (m), 1169 (m), 1005 (s), 941 (vs), 922 (vs), 816 (s), 728 (s), 693 (s), 623 (vs), 555 (vs), 518 (vs), 453 (vs), 404 (vs) cm⁻¹. EA anal. calc. for C₅₃H₃₆N₄O₈S₄: C 64.62, H 3.68, N 5.69, S 13.02; found: C 60.16, H 4.81, N 7.07, S 11.14.

HCP 18. HCP 18 generated in presence of 2 mL of AcOH. m = 0.402 g (95%). ATR-IR (ATR): ν = 1781 (vs), 1706 (vw), 1497 (m), 1367 (m), 1165 (m), 1007 (s), 943 (vs), 921 (vs), 815 (m), 729 (s), 689 (s), 621 (vs), 551 (vs), 520 (s), 452 (vs), 406 (vs) cm⁻¹. EA anal. calc. for C₆₅H₄₄N₄O₈S₄: C 68.64, H 3.90, N 4.93, S 11.28; found C 66.89, H 4.55, N 4.63, S 10.75.

HCP 20. HCP 20 generated in presence of 2 mL of AcOH. m = 0.392 g (97%). ATR-IR (ATR): ν = 1785 (vs), 1713 (vw), 1601 (vs), 1484 (s), 1415 (s), 1360 (m), 1171 (m), 1013 (s), 977 (vs), 944 (vs), 817 (s), 784 (m), 708 (vs), 625 (s), 555 (s), 462 (vs), 404 (vs) cm⁻¹. EA anal. calc. for C₆₁H₄₀N₄O₈S₄: C 67.51, H 3.72, N 5.16, S 11.82; found: C 65.16, H 4.21, N 5.07, S 10.14.

Acknowledgements

The authors gratefully acknowledged Dr Manuel Tsotsalas for his expertise in TGA.

Notes and references

1. L. I. Ching Wong, S. Barg, A. Menner, P. do Vale Pereira, G. Eda, M. Chowalla, E. Saiz and A. Bismarck, Polymer, 2014, 55, 395–402.
2. P. A. Côté, H. M. El-Kaderi, H. Furukawa, J. R. Hunt and O. M. Yaghi, J. Am. Chem. Soc., 2007, 129, 12914–12915.
3. R. W. Tilford, W. R. Gemmill, H.-C. zur Loye and J. J. Lavigne, Chem. Mater., 2006, 18, 5296–5301.
4. R. W. Tillford, S. J. Mygavero, P. J. Pellechia and J. J. Lavigne, Adv. Funct. Mater., 2008, 20, 2741–2746.
5. M. Mastalerz, Angew. Chem., Int. Ed., 2008, 47, 445–447.
6. P. A. Côté, A. I. Benin, N. W. Ockwig, M. O'Keefe, A. J. Matzger and O. M. Yaghi, Science, 2005, 310, 1166–1170.
7. H. M. El-Kaderi, J. R. Hunt, J. L. Mendoza-Cortès, P. A. Côté, R. E. Taylor, M. O'Keefe and O. M. Yaghi, Science, 2007, 316, 268–272.
8. A. I. Cooper, Adv. Mater., 2009, 21, 1291–1295.
9. J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu, C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak and A. I. Cooper, Angew. Chem., Int. Ed., 2007, 46, 8574–8578.
10. J.-X. Jiang, F. Su, H. Niu, C. D. Wood, N. L. Campbell, Y. Z. Khimyak and A. I. Cooper, Chem. Commun., 2008, 486–488.
11. J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, H. Niu, J. T. A. Jones, Y. Z. Khimyak and A. I. Cooper, J. Am. Chem. Soc., 2008, 130, 7710–7720.
12. R. Dawson, D. J. Adams and A. I. Cooper, Chem. Sci., 2011, 2, 1173–1177.
13. M. Saleh, H. M. Lee, K. C. Kemp and K. S. Kim, ACS Appl. Mater. Interfaces, 2014, 6, 7325–7333.
14. P. M. Budd, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J. Msayib and C. E. Tattershall, Chem. Commun., 2004, 230–231.
15. N. B. McKeown, P. M. Budd, K. J. Msayib, B. S. Ghanem, H. J. Kingston, C. E. Tattershall, S. Makhseed, K. J. Reynolds and D. Fritsch, Chem.–Eur. J., 2005, 11, 2610–2620.
16. P. M. Budd, N. B. McKeown and D. Fritsch, J. Mater. Chem., 2005, 15, 1977–1986.
17. N. B. McKeown and P. M. Budd, Chem. Soc. Rev., 2006, 35, 675–683.
18. N. B. McKeown and P. M. Budd, Macromolecules, 2010, 43, 5163–5176.
19. J. Weber, N. Du and M. D. Guiver, Macromolecules, 2011, 44, 1763–1767.
20. M. Carta, R. Malpass-Evans, M. Croad, Y. Rogan, J. C. Jansen, P. Bernardo, F. Bazzarelli and N. B. McKeown, Science, 2013, 339, 303–307.
21. J. Weber and A. Thomas, J. Am. Chem. Soc., 2008, 130, 6334–6335.
22. H. J. Mackintosh, P. M. Budd and N. B. McKeown, J. Mater. Chem., 2008, 18, 573–578.
23. B. S. Ghanem, K. J. Msayib, N. B. McKeown, K. D. M. Harris, Z. Pan, P. M. Budd, A. Butler, J. Selbie, D. Book and A. Walton, Chem. Commun., 2007, 67–69.
24. M. P. Tsyurupa and V. A. Davankov, React. Funct. Polym., 2002, 53, 193–203.
25. J. Germain, J. Hradil, J. M. J. Fréchet and F. Svec, Chem. Mater., 2006, 18, 4430–4435.
26. J. Germain, F. Svec and J. M. J. Fréchet, Chem. Mater., 2008, 20, 7069–7076.
27. W. G. Lu, D. Yuan, D. Zhao, C. I. Schilling, O. Plietzsch, T. Muller, S. Bräse, J. Guenther, J. Blümel, R. Krishna, Z. Li and H.-C. Zhou, Chem. Mater., 2010, 22, 5964–5972.
28. P. M. Budd, A. Butler, J. Selbie, K. Mahmood, N. B. McKeown, B. S. Ghanem, K. Msayib, D. Book and A. Walton, Phys. Chem. Chem. Phys., 2007, 9, 1802–1808.
29. C. D. Wood, B. Tan, A. Trewin, H. J. Niu, D. Bradshaw, M. J. Rosseinsky, Y. Z. Khimyak, N. L. Campbell, R. Kirk, E. Stockel and A. I. Cooper, Chem. Mater., 2007, 19, 2034–2048.
30. M. G. Schwab, A. Lennert, J. Pahnke, G. Jonschker, M. Koch, I. Senkovska, M. Rehahn and S. Kaskel, J. Mater. Chem., 2011, 21, 2131–2135.
31. C. D. Wood, B. T. Tan, A. Trewin, F. Su, M. J. Rosseinsky, D. Bradshaw, Y. Sun, L. Zhou and A. I. Cooper, Adv. Mater., 2008, 20, 1916–1921.
32. X. Feng, X. Ding and D. Jiang, Chem. Soc. Rev., 2012, 41, 6010–6022.
33. H. M. El-Kaderi, J. R. Hunt, J. L. Mendoza-Cortés, A. P. Côté, R. E. Taylor, M. O'Keeffe and O. M. Yaghi, Science, 2007, 316, 268–272.
34. H. Furukawa and O. M. Yaghi, J. Am. Chem. Soc., 2009, 131, 8875–8883.
35. J.-H. Fournier, T. Maris, J. D. Wuest, W. Guo and E. Galoppini, J. Am. Chem. Soc., 2003, 125, 1002–1006.
36. K. Severin, Dalton Trans., 2009, 5254–5264.
37. F. J. Uribe-Romo, J. R. Hunt, F. Hiroyasu, C. Klöck, M. O'Keeffe and O. M. Yaghi, J. Am. Chem. Soc., 2009, 131, 4570–4571.
38. J. L. Mendoza-Cortes, W. A. Goddard, H. Furukawa and O. M. Yaghi, J. Phys. Chem. Lett., 2012, 3, 2671–2675.
39. S. Ren, M. J. Bojdys, R. Dawson, A. Laybourn, Y. Z. Khimyak, D. J. Adams and A. I. Cooper, Adv. Mater., 2012, 24, 2357–2361.
40. P. Kuhn, M. Antonietti and A. Thomas, Angew. Chem., Int. Ed., 2008, 47, 3450–3453.
41. P. Kuhn, K. Kruger, A. Thomas and M. Antonietti, Chem. Commun., 2008, 5815–5817.
42. P. Kuhn, A. Thomas and M. Antonietti, Macromolecules, 2009, 42, 319–326.
43. M. J. Bojdys, J. Jeromenok, A. Thomas and M. Antonietti, Adv. Mater., 2010, 22, 2202–2205.
44. T. Ben, H. Ren, S. Ma, D. Cao, J. Lan, X. Jing, W. Wang, J. Xu, F. Deng, J. M. Simmons, S. Qiu and G. Zhu, Angew. Chem., Int. Ed., 2009, 48, 9457–9460.
45. J. R. Holst, E. Stöckel, D. J. Adams and A. I. Cooper, Macromolecules, 2010, 43, 8531–8538.
46. Q. Fang, Z. Zhuang, S. Gu, R. B. Kaspar, J. Zheng, J. Wang, S. Qiu and Y. Yan, Nat. Commun., 2014, 4503.
47. J. Bilbrey, http://www.materials360online.com, 5th August 2014.
48. A. Schade, L. Monnereau, T. Muller and S. Bräse, ChemPlusChem, 2014, 79, 1176–1182.
49. L. Monnereau, M. Nieger, T. Muller and S. Bräse, Adv. Funct. Mater., 2014, 24, 1054–1058.
50. T. Muller and S. Bräse, RSC Adv., 2014, 14, 6886–6907.
51. D. San-Yuang and W. Wang, Chem. Soc. Rev., 2013, 2013, 548–568.
52. R. Dawson, A. I. Cooper and D. J. Adams, Prog. Polym. Sci., 2012, 37, 560–563.
53. A. I. Cooper, Angew. Chem., Int. Ed., 2011, 50, 996–998.
54. T. Arne, Angew. Chem., Int. Ed., 2010, 49, 8328–8344.
55. J. Germain, J. M. J. Fréchet and F. Svec, Small, 2010, 49, 8328–8344.
56. W. W. Cleland, Biochemistry, 1964, 3, 480–482.
57. J. A. Burns, J. C. Butler, J. Moran and G. M. Whitesides, J. Org. Chem., 1991, 56, 2648–2650.
58. K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl. Chem., 1985, 57, 603–619.
59. G. Horváth and K. J. Kawazoe, J. Chem. Eng. Jpn., 1983, 16, 470–475.
60. M. Sava, I. Sava, V. Cozan and F. Tanasa, J. Appl. Polym. Sci., 2007, 106, 2185–2191.
61. J. Lee, H. W. Choi, Y. C. Nho and D. H. Suh, J. Appl. Polym. Sci., 2003, 88, 2339–2345.
62. R. W. Cranston and F. A. Inkley, Adv. Catal., 1957, 9, 143–154.
63. A. Mietrach, T. W. T. Muesmann, J. Christoffers and M. S. Wickleder, Eur. J. Inorg. Chem., 2009, 2009, 5328–5334.
64. D. C. Liao, K. H. Hsieh and S. C. Kao, J. Polym. Sci., Part A: Polym. Chem., 1995, 33, 481–491.
65. J. V. Crivello, J. Polym. Sci., Polym. Chem. Ed., 1976, 14, 159–182.

---

Footnote

† Electronic supplementary information (ESI) available: Details of thermal properties. See DOI: 10.1039/c5ra01463h

---