Amine post-functionalized POSS-based porous polymers exhibiting simultaneously enhanced porosity and carbon dioxide adsorption properties

Abstract

A novel hybrid porous polymer (HPP-1) is synthesized using octavinylsilsequioxane and 2,7-dibromo-9-fluorenone as monomers via Heck reaction. Subsequently, HPP-1 is post-functionalized by the conversion of deliberately introduced free ketone moieties into amine functionalities. Compared with HPP-1, the resulting material, HPP-1-amine, showed enhanced CO₂ uptake from 0.63 mmol g⁻¹ (HPP-1) to 1.01 mmol g⁻¹ (HPP-1-EDA, EDA = ethylenediamine) and 0.72 mmol g⁻¹ (HPP-1-HDA, HDA = hexamethylenediamine) at 298 K and 1 bar. Furthermore, the porosity of HPP-1-amine is not compromised, but enhanced with the BET specific surface area increasing from 529 m² g⁻¹ (HPP-1) to 651 m² g⁻¹ (HPP-1-EDA) and 615 m² g⁻¹ (HPP-1-HDA). Compared with HPP-1, the selectivity of CO₂ over N₂ of HPP-1-EDA increases nearly twice while that of HPP-1-HDA slightly decreases, indicating their potential applications in CO₂ storage and capture. Although the enhanced extent of CO₂/N₂ selectivity is not as high as other analogues, we provide a new possibility for post-synthetic amine functionalization of porous polymers for simultaneously enhancing porosity and CO₂ adsorption properties. The retained porosity won't limit their applications in other areas, such as heavy metal ion adsorption, ion channels and catalysis, etc.

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Introduction

Functional porous polymers are an emerging class of fascinating materials with considerable technological relevance because of their widespread application promise in many fields, such as gas storage, gas separation, heterogeneous catalysis, light-harvesting, sensors, and energy storage and conversion, etc.^1–6 Admittedly, functionality plays a decisive role in their applications. Functionality is traditionally achieved by selecting functional monomers through direct polymerization methodology.¹ For example, monomers bearing amino,⁷ carboxyl,^7,8 hydroxyl,^7,9 and metal–organic groups¹⁰ have been utilized as building blocks to construct novel porous polymers exhibiting significant improvement of the existing properties or new properties compared to analogous materials. Although functional monomers are easy to design and select, their synthetic procedures are usually tedious. Moreover, polymerization occasionally fails due to incompatibility between functional groups and catalysts in several metal-catalyzed reactions.

In contrast, another important strategy to achieve functionality, i.e., post-functionalization or post-synthetic modification (PSM) on an established porous polymers can overcome the disadvantage. While this approach has been well-developed in metal–organic frameworks (MOFs),¹¹ the exploitation in porous polymers is relatively limited but has developed rapidly in recent years. Several reactions, including amination,¹² nitration,¹³ click reactions,¹⁴ protonation¹⁵ and coordination,¹⁶ have been successfully applied to post-functionalize porous polymers. Similar to the former strategy, the incorporation of new functional groups into porous polymers by post-functionalization has led to materials with enhanced or specific functionality, such as enhanced CO₂ adsorption and selectivity,^12,13 catalytic activity¹⁶ and conductivity,¹⁷ etc. For example, Du et al. reported a class of post-modified polymers of intrinsic microporosity (PIMs) showing super-permeable characteristics and outstanding CO₂ separation performance by [2 + 3] cycloaddition of nitrile group with NaN₃ to form tetrazole rings.¹⁸ Bipyridine-containing conjugated microporous polymers (CMPs) have been post-metallated with rhenium, rhodium and iridium to form metal–organic CMPs showing excellent catalytic activity for reductive amination.¹⁹ Kiskan et al. reported post-functionalized phenolphthalein-based CMPs showing tunable CO₂ adsorption and photochemical activity for the photopolymerization of methyl methacrylate by merely tuning the pH value, and the post-functionalization process is switchable.¹⁵ However, this strategy suffers an obvious drawback, i.e., the porosity will be compromised, even lost because of the occupation of pore volume by functional groups, which may limit the applications of these materials in other fields, such as heavy metal ions adsorption and catalysis.²⁰

In the present study, we select a polyhedral oligomeric silsesquioxane (POSS) based hybrid porous polymer with a ketone functionality (HPP-1) as an established material for amine post-functionalization by the conversion of deliberately introduced free ketone moieties into amine functionalities (see Scheme 1). The selection of POSS-based porous polymer is motivated by specific characteristics of POSS units, including the ideal inorganic–organic hybrid structure, rigidity, polyfunctionality and high thermal stability, etc.^21,22 The selected ketone units are derived from 2,7-dibromo-9-fluorenone (Br-FO), which is a commercially available monomer and economical. Moreover, the amine post-functionalization process, i.e., the imine condensation reaction between ketone and amines is facile and mild. We explored the effect of the modification on the pore structure of the network and found that the porosity of the resultant amine-functionalized materials (HPP-1-amine) is not compromised, even increase to some extent. Moreover, the introduction of amine groups in the networks leads to materials with enhanced CO₂ capacity and CO₂/N₂ selectivity.

Scheme 1 Synthetic routes of hybrid porous polymer, HPP-1 and amine post-functionalized products, HPP-1-EDA and HPP-1-HDA. (i) Pd(OAc)₂/P(o-CH₃Ph)₃, DMF/Et₃N, 100 °C, 48 h; (ii) formic acid, MeOH, 80 °C, 72 h.

Results and discussion

Synthesis and characterization

Scheme 1 shows the synthetic routes of amine post-functionalized POSS-based porous polymers. HPP-1 was first synthesized from octavinylsilsesquioxanes (OVS) and Br-FO via Heck reaction, which was performed at 100 °C in N,N-dimethyl formamide for 48 h in the presence of Pd(OAc)₂/P(o-CH₃Ph)₃ as the catalyst.^23,24 Then the amine post-functionalization process was performed at 80 °C with a catalytic amount of formic acid by dispersing HPP-1 in the amine–methanol mixture,²⁵ thus yielding the amine-functionalized products, HPP-1-amine (amine = EDA, ethylenediamine; HDA, hexamethylenediamine).

The process was monitored by Fourier-transformed infrared spectroscopy (FT-IR) according to the change of the characteristic ν_C=O band from the fluorenone moieties and ν_C=N band after amine post-functionalization. Taking HPP-1-EDA as an example, the intensity of ν_C=O band at ca. 1720 cm⁻¹ largely decreased and the peak at ca. 1640 cm⁻¹ assigned to ν_C=N band appeared when the process time was 24 h. When the time was extended to 72 h, the ν_C=O band with weak intensity could still be observed (Fig. 1 and S1†), indicating that the full conversion of the ketone in HPP-1 to the imine moiety in HPP-1-EDA didn't occur. This finding was also found in HPP-1-HDA (Fig. S2†). The conversion efficiencies are 68.6% and 52.2% for HPP-1-EDA and HPP-1-HDA, respectively, calculated from the intensity decrease degree of ν_C=O band using the unchanged ν_C=C band at 1603 cm⁻¹ as the reference. We speculate that the relatively low conversion efficiencies can be caused by two reasons. The first one is that the imine condensation reaction in this study is a kind of heterogeneous reaction due to the insolubility of HPP-1 in common solvents, unlike the high efficiencies found in the homogeneous reactions for preparing small organic molecules.²⁵ Another one is that organic amine molecules couldn't reach the ketone groups embedded in the closed pores, which may exist in the porous network. In addition, the characteristic Si–O–Si stretching vibration peaks for those materials were observed at ca. 1130 cm⁻¹.

Fig. 1 The FT-IR spectra enlarged from 2000 cm⁻¹ to 800 cm⁻¹ of HPP-1, HPP-1-EDA at 24 h and 72 h.

The reaction process and the identification of the local structures of HPP-1 and HPP-1-amine were further determined by the solid-state ¹³C CP/MAS NMR and ²⁹Si NMR spectroscopy. The signal at δ = 191 ppm attributed to the ketone carbon atoms (C=O) largely decreased, but can be still detected after amine functionalization, while a new signal at δ = 163 ppm assigned to the imine carbon atoms (C=N) appeared (Fig. 2). These results revealed the amine-functionalization process successfully happened but the conversion was incomplete, consistent with the FT-TR results. The resonances arising from other carbon atoms can be ascribed as shown in Fig. 2.

Fig. 2 Solid-state ¹³C CP/MAS NMR spectra of HPP-1, HPP-1-EDA and HPP-1-HDA. Asterisk at ca. 49 ppm denotes the residual methanol derived from the extraction process.

The ²⁹Si NMR spectra showed three signals at δ = ∼−61, ∼−70 and ∼−77 ppm, which were attributed to the T₁, T₂ and T₃ units [T_n: CSi(OSi)_n(OH)_3−n] (Fig. 3). Scheme 2 shows the possible frameworks of HPP-1 and HPP-1-amine (HPP-1-EDA as an example). For HPP-1, a few POSS cages collapsed during the synthesis and T₁ and T₂ units were formed. Such destruction could be attributed to the distortion of POSS units to link the rigid FO units and the presence of triethylamine (Et₃N) and acid; Et₃N served as the acid adsorbent and acid, i.e., HBr was produced in the Heck reaction. This finding is consistent with our previous reports.^23,24 Moreover, it is found that such destruction continued to occur in the amine post-functionalization process and new T₁ and T₂ units were formed. This can be proven by the decreased T₃/(T₃ + T₂ + T₁) ratio from 0.58 (HPP-1) to 0.48 (HPP-1-EDA) and 0.50 (HPP-1-HDA) calculated from the relative intensity of the T₃, T₂ and T₁ signals. The consequent destruction for HPP-1-amine was obviously due to the addition of alkylamines, which are a kind of organic base. In addition, the appearance of peak from −90 to −110 ppm may be ascribed to Q_n (Si(OSi)_n(OH)_4−n) species²⁶ and suggests that Si–C bonds have been partially cleaved. However, most of the POSS cages remained in the porous networks. Except FT-IR and NMR measurements, elemental analysis is another important means to prove the successful conversion; the nitrogen content increased from 0 (HPP-1) to 4.59 wt% and 3.50 wt% for HPP-1-EDA and HPP-1-HDA, respectively.

Fig. 3 Solid-state ²⁹Si NMR spectra of HPP-1, HPP-1-EDA and HPP-1-HDA. The T₃/(T₃ + T₂ + T₁) ratios were calculated from the relative intensity of the T₃, T₂ and T₁ signals.

Scheme 2 Possible frameworks of HPP-1 and HPP-1-amine (HPP-1-EDA as an example) showing the destruction of POSS units, the formation of T₁ and T₂ units and possible hydrogen bond interactions.

Thermal stability and morphology

The thermal stabilities of the polymers were determined by thermogravimetric analysis (TGA) under N₂ at 10 °C min⁻¹ (Fig. S3†). HPP-1 exhibited high thermal decomposition temperature (T_{d,5 wt%}) of up to 545 °C, which is higher than other POSS-based porous materials.^23,24,26,27 As expected, much lower decomposition temperatures were found in HPP-1-EDA and HPP-1-HDA with T_{d,5 wt%} of ca. 330 °C and 300 °C. The weight loss occurring at <100 °C is attributed to some residual water/solvent in the porous networks, which can be coordinated to free amines through hydrogen bonding. After that, slower degradation could be attributed to the alkyl amine groups. This finding is consistent with a previous report.²⁸ Because of initial loss of some residual water/solvent and alkyl amine groups, the char yield of HPP-1 was higher than those of HPP-1-EDA and HPP-1-HDA.

Consistent with other POSS-based porous polymers, HPP-1 and HPP-1-amine were amorphous and no long-range crystallographic order was observed in powder X-ray diffraction (PXRD) measurements (Fig. S4†). Field-emission scanning electron microscopy (FE-SEM) measurements revealed that there is no obvious change of morphologies with irregular shapes after amine post-functionalization (Fig. 4a and S5†). High-resolution transmission electron microscopy (HR-TEMS) images are shown in Fig. 4b and S6.† The translucent TEM images are indicative of porous, not dense, structures of materials with relatively uniform pore diameters but no evidence of long-range ordering. The results are consistent with other POSS-based porous materials.^{22–24,26,27}

Fig. 4 FE-SEM (a) and HR-TEM (b) images of HPP-1 as an example.

Porosity

The porosity of the polymers was investigated by nitrogen adsorption and desorption experiments at 77 K and Table 1 shows the detailed porosity of these polymers. All the polymers appeared as IUPAC type I N₂ isotherms with some type IV isotherm characteristics at higher relative pressures (Fig. 5a). All the isotherms showed a sharp uptake at low relative pressure and a gradually increasing uptake at higher relative pressures, suggesting the presence of micropores and mesopores within the networks. The Brunauer–Emmett–Teller surface areas (S_BET) of HPP-1, HPP-1-EDA and HPP-1-HDA were calculated to be 529, 651 and 615 m² g⁻¹. Total pore volumes (V_total) were 0.37, 0.46 and 0.47 cm³ g⁻¹. It is significantly noted that the porosity increased along with amine introduction, unlike the compromised porosity found in other amine-tethered porous materials.^12,28,29 We speculate that this unusual phenomenon can be explained by two reasons. First, new destruction of POSS cages happened during the amine-functionalized process evidenced by the decreased T₃/(T₃ + T₂ + T₁) ratios as mentioned above. The fact that the destruction contributing to increase the porosity has been proved by Chaikittisilp et al., obtaining a POSS-containing network, PSN-5, with an ultrahigh S_BET of 2500 m² g⁻¹, representing the highest surface area for the siloxane-based porous materials.²⁷ For those materials with no destruction of siloxane cleavage, dense silica and organic matrixes were formed to stabilize the porous framework and the surface areas of such materials are limited to a certain value. On the contrary, the destruction of the siloxane parts prevents the formation of dense silica and organic matrixes, leading to an increased surface area.

Table 1 Porosity data of HPP-1 and HPP-1-amine

Sample	Surface area/m^2 g^−1		Pore volume/cm^3 g^−1			CO2 uptake^e/mmol g^−1		N2 uptake^f/mmol g^−1	Qst^g/kJ mol^−1	S^h
	SBET^a	Smicro^b	Vtotal^c	Vmicro^d	Vmicro/Vtotal	273 K	298 K	298 K		298 K
a Surface area calculated from N2 adsorption isotherm using the BET method.b Microporous surface area calculated from N2 adsorption isotherm using t-plot method.c Total pore volume calculated at P/P0 = 0.99.d Micropore volume derived using the t-plot method based on the Halsey thickness equation.e At 1 bar.f At 1 bar.g At zero coverage.h Selectivity is calculated from Henry equation.
HPP-1	529	275	0.37	0.14	0.38	1.15	0.63	0.034	34	27.7
HPP-1-EDA	651	282	0.46	0.13	0.28	1.69	1.01	0.036	49	49.3
HPP-1-HDA	615	224	0.47	0.11	0.23	1.23	0.72	0.035	40	25.2

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Fig. 5 (a) Nitrogen adsorption (closed symbols) and desorption (open symbols) isotherms for HPP-1, HPP-1-EDA and HPP-1-HDA. For clarify, HPP-1-EDA and HPP-1-HDA are shifted vertically by 150 cm³ g⁻¹ and 300 cm³ g⁻¹; (b) pore size distribution curves of HPP-1, HPP-1-EDA and HPP-1-HDA.

Second, free activity of alkyl amine chains in the pores may be restricted by hydrogen bond interactions. As shown in Scheme 2, during the formation of HPP-1 framework and amine post-functionalization process, several Si–OH groups were produced due to the destruction of POSS units and hydrogen bonds could be formed between hydrogen bond donors, including –NH₂ and –OH groups, and hydrogen bond acceptors, including –NH₂, –OH, and even imine and residual ketone groups. Possible hydrogen bonds included O–H⋯O(H)Si, O–H⋯N(H₂)C, O–H⋯O=C, (H)N–H⋯O(H)Si, (H)N–H⋯O=C, (H)N–H⋯N(H₂)C and (H)N–H⋯N=C, etc. These various hydrogen bond interactions could efficiently limit the free activity of alkyl amine chains in the pore and retain more free pore volume. Unfortunately, because the products are cross-linked materials and insoluble in common solvents, it is difficult to prove the presence of hydrogen bonds determined by traditional techniques, such as IR and ¹H NMR. However, the presence of hydrogen bonds have been widely found in many silanol compounds.^30,31 For example, in our previous report, we found that the hydrogen bond interactions existed in incompletely condensed silsesquioxanes (POSS-mono-ol, POSS-diol and POSS-triol).³¹

Along with the enhanced surface area, the pore size also appeared no large change, in contrast to the reduced pore size occupied by the bulky amine groups found in other amine-tethering products.^12,28,29 All the porous networks showed similar pore size distribution with major micropore diameters at 1.4 nm and 1.8 nm, and mesopore diameters at 2.8 nm and 3.8 nm before and after the amine-tethering process (Fig. 5b). Additionally, lower porosity for HPP-HDA than HPP-1-EDA is apparently due to the larger space volume of HDA than EDA.

Carbon dioxide sorption

To evaluate their potential applications in CO₂ capture, CO₂ adsorption experiments were carried out. As expected, the introduction of alkylamine groups in HPP-1 resulted in materials with enhanced CO₂ sorption properties at low pressures (Fig. 6a and S8†). The CO₂ uptakes of HPP-1, HPP-1-EDA and HPP-1-HDA were 1.15, 1.69 and 1.23 mmol g⁻¹ at 273 K, and 0.63, 1.01 and 0.72 mmol g⁻¹ at 298 K, which were measured up to 1 bar. Apparently, one factor leading to the enhancement is the increased porosity for the materials with higher surface area and pore volume after amine post-functionalization. Another vital factor is the isosteric heat (Q_st) of CO₂ adsorption, which represents the affinity between the sorbent and CO₂. Indeed, the Q_st at low coverage, calculated from CO₂ isotherms collected at 273 K and 298 K employing the Clausius–Clapeyron equation, increased substantially from 34 kJ mol⁻¹ for the original HPP-1 to 49 kJ mol⁻¹ and 40 kJ mol⁻¹ for the amine-functionalized HPP-1-EDA and HPP-1-HDA at zero coverage (Fig. 6b), further confirming the great efficiency of our amine-functionalization strategy on ketone sites. This finding is consistent with the successful linking the amine on aldehyde anchors.²⁸ Moreover, unlike the classical amine supported materials (e.g., mesoporous silica and alumina),³² it is not necessary to heat for reactivating HPP-1-amine between variable temperature adsorption measurements, thus suggesting potentially diminishing energy penalty for adsorption-desorption cycles. The CO₂ cyclic capacity of HPP-1-EDA and HPP-1-HDA was also determined by saturating CO₂ up to 1 bar at 273 K followed by a high vacuum for 100 min at 80 °C. It is found that there was no apparent loss in capacity after 10 cycles (Fig. S9†), thus indicating that adsorption during each cycle was completed and these materials possessed good stability for regeneration.

Fig. 6 (a) CO₂ adsorption isotherms of HPP-1, HPP-1-EDA and HPP-1-HDA at 273 K (closed symbols) and 298 K (open symbols), and N₂ adsorption of HPP-1-EDA at 298 K as an example; (b) isosteric heats of carbon dioxide adsorption of HPP-1, HPP-1-EDA and HPP-1-HDA.

The high Q_st of CO₂ adsorption for the HPP-1-amine motivated us to assess the potential as prospective separation agents because the isosteric heat also plays a major role in determining the adsorption selectivity. Thus we measured the N₂ adsorption isotherms of the materials at 298 K. The results showed that HPP-1-amine adsorbed more N₂ than HPP-1 at all pressure between 0 and 1.0 bar, which may be due to the additional polarizing sites and the enhancement in specific surface area. One of the common methods to calculate the gas adsorption selectivity involves the use of Henry equation.³³ To calculate the selectivity factor (S) for adsorption of CO₂ over N₂ from the corresponding Henry's constants, a nonlinear fitting of the adsorption isotherm was performed using the Toth model (Fig. S10–S12†). The calculated values are listed in Table 1. Compared with the CO₂/N₂ selectivity of HPP-1 (S: 27.7), nearly twofold increase and slight decrease were found in those of HPP-1-EDA (S: 49.3) and HPP-1-HDA (S: 25.2), respectively. The values are higher or comparable to the corresponding values of some MOFs³⁴ and nitrogen-rich porous organic polymers.³⁵ For HPP-1-EDA, enhanced CO₂/N₂ selectivity confirms that our unique amine functionalization process is an effective mean to not only improve the CO₂ capacity but also promote its selectivity of CO₂ over N₂. This finding is consistent with other amine-functionalized porous materials.^12,28,29 However, the enhanced extent of the selectivity is not as high as other analogues; for example, some of them even showed a more than tenfold selectivity enhancement.^12,29 For HPP-1-HDA, its CO₂ and N₂ capacities were also improved. However, the enhanced extent of CO₂ capacity doesn't exceed that of N₂ capacity, thus leading to a slight decline of selectivity. We speculated these results can be explained by two reasons. First, the surface areas after amine functionalization were improved and the resulting products adsorb more N₂ as shown in the N₂ isotherm at 298 K while adsorbing more CO₂. Second, the conversion of ketone into imine is incomplete (68.6% and 52.2% for HPP-1-EDA and HPP-1-HDA) and the amine loading capacity is not very high. However, there is still some upside potential for the conversion by optimizing the reaction, which may promote the selectivity. Additionally, the surface areas of HPP-1-EDA and HPP-1-HDA are still relatively low, which is not also beneficial to adsorb CO₂.

Although the values of CO₂ selectivity are lower than some amine-functionalized porous materials in recent reports,^12,29 herein we provide a new possibility for post-synthetic amine functionalization of porous materials for improving the CO₂ capacity and selectivity without compromising the porosity. This retaining porosity won't limit the resulting materials to be applied in other areas, such as heavy metal ion adsorption, ion channels and catalysis, etc. For example, for the heavy metal ion adsorption using porous materials as solid absorbents, two important factors should be considered: (i) the species and content of functional groups representing the potential loading capacity of the metal ions; and (ii) the porosity indicating the ease or difficulty of metal ions accessing into the pore.²⁰ For common post-functionalized porous materials, the compromised porosity made the process of metal ions accessing into the pores more difficult. On the contrast, herein the enhanced surface area and pore volume of our amine-functionalized materials might make the process easier and thus effective heavy metal ions capacity would be achieved. It is similar when using in catalysis. Current materials could be used as support materials to load metal ion (such as palladium) and thus act as catalyst. It is known that the catalytic efficiency commonly depend on the content of metal ion. The retaining porosity also might make the process of metal ion loading on the networks easier and lead to higher metal ion loading capacity.

Conclusions

In summary, we reported novel amine post-functionalized POSS-based porous polymers (HPP-1-amine) by the conversion of deliberately introduced free ketone moieties into amine functionalities using a hybrid porous polymer (HPP-1) containing POSS and fluorenone units as the support material, which is synthesized based on octavinylsilsequioxane and 2,7-dibromo-9-fluorenone via Heck reaction. We found that the resultant materials exhibited simultaneously enhanced carbon dioxide adsorption properties and enhanced porosity, unlike the compromised porosity found in other amine post-functionalized porous materials. The CO₂ uptake increased from 0.63 mmol g⁻¹ (HPP-1) to 1.01 mmol g⁻¹ (HPP-1-EDA) at 298 K and 1 bar, while the BET specific surface area increased from 529 m² g⁻¹ (HPP-1) to 651 m² g⁻¹ (HPP-1-EDA). Compared with HPP-1, the selectivity of CO₂ over N₂ of HPP-1-EDA increased nearly twice while that of HPP-1-HDA slightly decreased, indicating their potential applications in CO₂ capture. Although the enhanced extent of CO₂ selectivity is not as high as other analogues, the retaining porosity won't limit the applications of the resulting materials in other areas. Further investigations will focus on three aspects: (i) increasing the porosity of the starting porous polymers containing POSS and fluorenone units by altering the monomer species and reaction conditions; (ii) optimizing the amine functionalization method and enhancing the amine loading capacity; (iii) utilizing the amine-functionalized porous polymers in various areas, including CO₂ capture, heavy metal ion adsorption, ion channels and catalysis, etc.

Experimental section

Materials

Unless otherwise noted, all reagents were obtained from commercial suppliers and used without further purification. OVS was synthesized by the previous report.³⁶ N,N-Dimethylformamide (DMF) was first dried over CaH₂ at 80 °C for 12 h, distilled under vacuum pressure and stored with 4 Å molecule sieves prior to use. Triethylamine (Et₃N) was dried over CaH₂ and used freshly.

Characterization

Fourier transform infrared (FTIR) spectra was recorded on a Bruker Tensor27 spectrophotometer. Solid-state ¹³C cross-polarization/magic-angle-spinning (CP/MAS) NMR and ²⁹Si MAS NMR spectra were performed on Bruker AVANCE-500 NMR Spectrometer operating at a magnetic field strength of 9.4 T. The resonance frequencies at this field strength were 125 and 99 MHz for ¹³C NMR and ²⁹Si NMR, respectively. A Chemagnetics 5 mm triple-resonance MAS probe was used to acquire ¹³C and ²⁹Si NMR spectra. ²⁹Si MAS NMR spectra with high power proton decoupling were recorded using a π/2 pulse length of 5 μs, a recycle delay of 120 s and a spinning rate of 5 kHz. Elemental analyses were conducted using an Elementar vario EL III elemental analyzer.

Field-emission scanning electron microscopy (FE-SEM) experiments were performed by using HITACHI S4800 Spectrometer. The high-resolution transmission electron microscopy (HR-TEM) experiments were performed by using a JEM 2100 electron microscope (JEOL, Japan) with an acceleration voltage of 200 kV.

Thermogravimetric analyses were performed with a Mettler Toledo SDTA-854 TGA system in nitrogen at a heating rate of 10 °C min⁻¹ to 800 °C. Powder X-ray diffraction (PXRD) were performed using a Riguku D/MAX 2550 diffractometer under Cu-Kα radiation, 40 kV, 200 mA with a scanning rate of 10° min⁻¹ (2θ).

Nitrogen sorption isotherm measurements were performed on a Micro Meritics surface area and pore size analyzer. Before measurement, samples were degassed at 100 °C for least 12 h. A sample of ca. 100 mg and a UHP-grade nitrogen (99.999%) gas source were used in the nitrogen sorption measurements at 77 K and collected on a Quantachrome Quadrasorb apparatus. BET surface areas were determined over a P/P₀ range from 0.01 to 0.20. Nonlocal density functional theory (NL-DFT) pore size distributions were determined using the carbon/slit-cylindrical pore mode of the Quadrawin software. Carbon dioxide (CO₂) adsorption isotherms at 298 K and 273 K, and nitrogen adsorption isotherms at 298 K were measured on a Micrometrics ASAP 2020. Prior to the measurements, the samples were degassed at 150 °C for at least 10 h.

Synthesis of hybrid porous polymer, HPP-1

OVS (632 mg, 1 mmol), palladium acetate (90 mg, 0.4 mmol) and tris(2-methylphenyl)phosphine (193 mg, 0.94 mmol) were dissolved in a DMF/Et₃N solution (45 mL/15 mL) under argon. The mixture was stirred and bubbled by argon under stirring for 0.5 h at room temperature and 2,7-dibromo-9-fluorenone (Br-FO) (1.35 g, 4 mmol) was added. The resulting solution was then heated at 100 °C for 48 h and cooled to room temperature. The mixture was filtered and the residue was washed with THF, chloroform, water, methanol and acetone. Further purification of the sample was carried out by extraction with THF for 24 h and methanol for 24 h. The product was recovered by filtration, and dried under reduced pressure at 70 °C for 48 h. HPP-1 was afforded as a red-brown solid (1.47 g). Yield: 109%. The yield was calculated based on hypothetical 100% polycondensation. Elemental analysis calc. (wt%) for C₆₈H₄₀Si₈O₁₂: C 61.05, H 3.01; found C 54.70, H 3.64.

Synthesis of HPP-1-EDA

HPP-1 (0.30 g), ethylenediamine (3.00 g) and two drops of formic acid were added into 50 mL of MeOH. The resulting mixture was stirred and refluxed for 72 h. After cooling to room temperature, the mixture was filtrated and the residue was washed with MeOH three times. The product was dried under vacuum at 70 °C for 24 h and afforded as a brick-red solid (0.32 g). Elemental analysis: found C 58.45, H 4.46, N 4.59.

Synthesis of HPP-1-HDA

The synthesis procedure of HPP-1-HDA was similar to that of HPP-1-EDA except that ethylenediamine (3.00 g) was replaced by hexamethylenediamine (3.00 g). Elemental analysis: found C 60.19, H 4.91, N 3.50.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (21502105, 21574075, 21274080 and 21274081), the National Science Foundation of Shandong Province (2015ZRE27053 and ZR2015BQ008), Shandong special fund for independent innovation and achievements transformation (No. 2014ZZCX01101) and the Fundamental Research Funds of Shandong University (2014GN009).

References

1. D. Wu, F. Xu, B. Sun, R. Fu, H. He and K. Matyjaszewski, Chem. Rev., 2012, 112, 3959–4015; R. Dawson, A. I. Cooper and D. J. Adams, Prog. Polym. Sci., 2012, 37, 530–563; Y. Xu, S. Jin, H. Xu, A. Nagai and D. Jiang, Chem. Soc. Rev., 2013, 42, 8012–8031; T. Muller and S. Bräse, RSC Adv., 2014, 4, 6886–6907; U. H. F. Bunz, K. Seehafer, F. L. Geyer, M. Bender, I. Braun, E. Smarsly and J. Freudenberg, Macromol. Rapid Commun., 2014, 35, 1466–1496; P. J. Waller, F. Gandara and O. M. Yaghi, Acc. Chem. Res., 2015, 48, 3053–3063.
2. A. I. Cooper, Adv. Mater., 2009, 21, 1291–1295; X. Du, Y. L. Sun, B. E. Tan, Q. F. Teng, X. J. Yao, C. Y. Sun and W. Wang, Chem. Commun., 2010, 46, 970–972; A. Thomas, Angew. Chem., Int. Ed., 2010, 49, 8328–8344; J. T. A. Jones, T. Hasell, X. Wu, J. Bacsa, K. E. Jelfs, M. Schmidtmann, S. Y. Chong, D. J. Adams, A. Trewin, F. Schiffman, F. Cora, B. Slater, A. Steiner, G. M. Day and A. I. Cooper, Nature, 2011, 474, 367–371.
3. A. Kumar, D. G. Madden, M. Lusi, K.-J. Chen, E. A. Daniels, T. Curtin, J. J. Perry and M. J. Zaworotko, Angew. Chem., Int. Ed., 2015, 54, 14372–14377; Z. Xiang, R. Mercado, J. M. Huck, H. Wang, Z. Guo, W. Wang, D. Cao, M. Haranczyk and B. Smit, J. Am. Chem. Soc., 2015, 137, 13301–13307; C. H. Lau, K. Konstas, A. W. Thornton, A. C. Y. Liu, S. Mudie, D. F. Kennedy, S. C. Howard, A. J. Hill and M. R. Hill, Angew. Chem., Int. Ed., 2015, 54, 2669–2673; Y. Liao, J. Weber and C. F. J. Faul, Macromolecules, 2015, 48, 2064–2073.
4. M. Rose, ChemCatChem, 2014, 6, 1166–1182; Q. Sun, Z. Dai, X. Meng, L. Wang and F.-S. Xiao, ACS Catal., 2015, 5, 4556–4567; T.-T. Liu, Z.-J. Lin, P.-C. Shi, T. Ma, Y.-B. Huang and R. Cao, ChemCatChem, 2015, 7, 2340–2345.
5. K. Zhang, B. Tieke, F. Vilela and P. J. Skabara, Macromol. Rapid Commun., 2011, 32, 825–830; A. Patra and U. Scherf, Chem.–Eur. J., 2012, 18, 10074–10080; X. M. Liu, Y. H. Xu and D. L. Jiang, J. Am. Chem. Soc., 2012, 134, 8738–8741; J.-X. Jiang, A. Trewin, D. J. Adams and A. I. Cooper, Chem. Sci., 2011, 2, 1777–1781; J. L. Novotney and W. R. Dichtel, ACS Macro Lett., 2013, 2, 423–426; D. Wang, W. Yang, L. Li, S. Feng and H. Liu, RSC Adv., 2014, 4, 59877–59884; W. Yang, X. Jiang and H. Liu, RSC Adv., 2015, 5, 12800–12806.
6. Y. Kou, Y. Xu, Z. Guo and D. Jiang, Angew. Chem., Int. Ed., 2011, 50, 8753–8757; X. Zhuang, F. Zhang, D. Wu, N. Forler, H. Liang, M. Wagner, D. Gehrig, M. R. Hansen, F. Laquai and X. Feng, Angew. Chem., Int. Ed., 2013, 52, 9668–9672.
7. R. Dawson, D. J. Adams and A. I. Cooper, Chem. Sci., 2011, 2, 1173–1177.
8. J. Weber, N. Y. Du and M. D. Guiver, Macromolecules, 2011, 44, 1763–1767.
9. A. P. Katsoulidis and M. G. Kanatzidis, Chem. Mater., 2011, 23, 1818–1824; S.-H. Jia, X. Ding, H.-T. Yu and B.-H. Han, RSC Adv., 2015, 5, 71095–71101.
10. Z. Xie, C. Wang, K. E. deKrafft and W. Lin, J. Am. Chem. Soc., 2011, 133, 2056–2059; R. K. Totten, Y.-S. Kim, M. H. Weston, O. K. Farha, J. T. Hupp and S. T. Nguyen, J. Am. Chem. Soc., 2013, 135, 11720–11723.
11. Z. Wang and S. M. Cohen, Chem. Soc. Rev., 2009, 38, 1315–1329.
12. W. Lu, J. P. Sculley, D. Yuan, R. Krishna, Z. Wei and H.-C. Zhou, Angew. Chem., Int. Ed., 2012, 51, 7480–7484; S. Sung and M. P. Suh, J. Mater. Chem. A, 2014, 2, 13245–13249; W. Lu, M. Bosch, D. Yuan and H.-C. Zhou, ChemSusChem, 2015, 8, 433–438; B. Satilmis, M. N. Alnajrani and P. M. Budd, Macromolecules, 2015, 48, 5663–5669; C. H. Lau, K. Konstas, C. M. Doherty, S. Kanehashi, B. Ozcelik, S. E. Kentish, A. J. Hill and M. R. Hill, Chem. Mater., 2015, 27, 4756–4762; D. Lee, C. Zhang and H. Gao, Macromol. Chem. Phys., 2015, 216, 489–494.
13. C. Shen and Z. Wang, J. Phys. Chem. C, 2014, 118, 17585–17593.
14. B. Kiskan and J. Weber, ACS Macro. Lett., 2012, 1, 37–40; H. Lim and J. Y. Chang, Macromolecules, 2010, 43, 6943–6945.
15. B. Kiskan, M. Antonietti and J. Weber, Macromolecules, 2012, 45, 1356–1361.
16. P. Zhang, Z.-A. Qiao, X. Jiang, G. M. Veith and S. Dai, Nano Lett., 2015, 15, 823–828; A. M. Shultz, O. K. Farha, J. T. Hupp and S. T. Nguyen, Chem. Sci., 2011, 2, 686–689.
17. H. Bildirir, I. Osken, T. Ozturk and A. Thomas, Chem.–Eur. J., 2015, 21, 9306–9311.
18. N. Du, H. B. Park, G. P. Robertson, M. M. Dal-Cin, T. Visser, L. Scoles and M. D. Guiver, Nat. Mater., 2011, 10, 372–375.
19. J.-X. Jiang, C. Wang, A. Laybourn, T. Hasell, R. Clowes, Y. Z. Khimyak, J. Xiao, S. J. Higgins, D. J. Adams and A. I. Cooper, Angew. Chem., Int. Ed., 2011, 50, 1072–1075.
20. N. Saman, K. Johari and H. Mat, Ind. Eng. Chem. Res., 2014, 53, 1225–1233; H. Cui, Y. Qian, Q. Li, Z. Wei and J. Zhai, Appl. Clay Sci., 2013, 72, 84–90.
21. R. M. Laine and M. F. Roll, Macromolecules, 2011, 44, 1073–1109; D. B. Cordes, P. D. Lickiss and F. Rataboul, Chem. Rev., 2010, 110, 2081–2173.
22. W. Chaikittisilp, A. Sugawara, A. Shimojima and T. Okubo, Chem. Mater., 2010, 22, 4841–4843; W. Chaikittisilp, A. Sugawara, A. Shimojima and T. Okubo, Chem.–Eur. J., 2010, 16, 6006–6014; M. F. Roll, J. W. Kampf, Y. Kim, E. Yi and R. M. Laine, J. Am. Chem. Soc., 2010, 132, 10171–10183; I. Nischang, O. Brüggemann and I. Teasdale, Angew. Chem., Int. Ed., 2011, 50, 4592–4596; Y. Wu, D. Wang, L. Li, W. Yang, S. Feng and H. Liu, J. Mater. Chem. A, 2014, 2, 2160–2167.
23. D. Wang, L. Xue, L. Li, B. Deng, S. Feng, H. Liu and X. Zhao, Macromol. Rapid Commun., 2013, 34, 861–866.
24. D. Wang, W. Yang, L. Li, X. Zhao, S. Feng and H. Liu, J. Mater. Chem. A, 2013, 1, 13549–13558; D. Wang, W. Yang, S. Feng and H. Liu, Polym. Chem., 2014, 5, 3634–3642.
25. P. Papanikolaou, J. Mohanraj, A. Czapik, M. Gdaniec, G. Accorsi and P. Akrivos, Dalton Trans., 2013, 42, 3357–3365; K. Venkatesan, S. Dhivya, J. Rethavathi and S. Narasimhan, J. Chem. Pharm. Res., 2012, 4, 4477–4483.
26. Y. Peng, T. Ben, J. Xu, M. Xue, X. Jing, F. Deng, S. Qiu and G. Zhu, Dalton Trans., 2011, 40, 2720–2724.
27. W. Chaikittisilp, M. Kubo, T. Moteki, A. Sugawara-Narutaki, A. Shimojima and T. Okubo, J. Am. Chem. Soc., 2011, 133, 13832–13835.
28. V. Guillerm, Ł. J. Weseliński, M. Alkordi, M. I. H. Mohideen, Y. Belmabkhout, A. J. Cairns and M. Eddaoudi, Chem. Commun., 2014, 50, 1937–1940.
29. T. M. McDonald, D. M. D'Alessandro, R. Krishna and J. R. Long, Chem. Sci., 2011, 2, 2022–2028; N. Planas, A. L. Dzubak, R. Poloni, L.-C. Lin, A. McManus, T. M. McDonald, J. B. Neaton, J. R. Long, B. Smit and L. Gagliardi, J. Am. Chem. Soc., 2013, 135, 7402–7405; Q. Yan, Y. Lin, C. Kong and L. Chen, Chem. Commun., 2013, 49, 6873–6875; Y. Lin, H. Lin, H. Wang, Y. Suo, B. Li, C. Kong and L. Chen, J. Mater. Chem. A, 2014, 2, 14658–14665.
30. M. Fukawa, T. Sato and Y. Kabe, Chem. Commun., 2015, 51, 14746–14749; Y. Kawakami, M. Fukawa, A. Yanase, Y. Furukawa, Y. Nagata, E. Suzuki, T. Horikawa and Y. Kabe, J. Organomet. Chem., 2015, 799–800, 265–272; S.-i. Kondo, N. Okada, R. Tanaka, M. Yamamura and M. Unno, Tetrahedron Lett., 2009, 50, 2754–2757; S. Spirk, M. Nieger, F. Belaj and R. Pietschnig, Dalton Trans., 2009, 163–167.
31. H. Liu, S.-i. Kondo, R. Tanaka, H. Oku and M. Unno, J. Organomet. Chem., 2008, 693, 1301–1308.
32. B. Dutcher, M. Fan and A. G. Russell, ACS Appl. Mater. Interfaces, 2015, 7, 2137–2148; C. Chen, J. Kim and W.-S. Ahn, Korean J. Chem. Eng., 2014, 31, 1919–1934.
33. E. Neofotistou, C. D. Malliakas and P. N. Trikalitis, Chem.–Eur. J., 2009, 15, 4523–4527; B. Wang, A. P. Côté, H. Furukawa, M. O'Keeffe and O. M. Yaghi, Nature, 2008, 453, 207–211.
34. R. Banerjee, H. Furukawa, D. Britt, C. Knobler, M. O'Keeffe and O. M. Yaghi, J. Am. Chem. Soc., 2009, 131, 3875–3877; A. Demessence, D. M. D'Alessandro, M. L. Foo and J. R. Long, J. Am. Chem. Soc., 2009, 131, 8784–8786.
35. S. Hug, M. B. Mesch, H. Oh, N. Popp, M. Hirscher, J. Senkerd and B. V. Lotsch, J. Mater. Chem. A, 2014, 2, 5928–5936.
36. R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuki, Chem. Rev., 1995, 95, 1409–1430.

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Footnote

† Electronic supplementary information (ESI) available: FT-IR spectra, TGA curves, XRD patterns and BET plots of HPP-1, HPP-EDA and HPP-1-HDA, FE-SEM and HR-TEM images of HPP-EDA and HPP-1-HDA, CO₂ adsorption–desorption isotherms of HPP-1-EDA and HPP-1-HDA at 273 K and 298 K, ten cycles of CO₂ uptakes of HPP-1-EDA and HPP-1-HDA at 273 K, Toth model fitting of CO₂ and N₂ adsorption isotherms of HPP-1, HPP-EDA and HPP-1-HDA at 298 K. See DOI: 10.1039/c5ra26617c

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