Hybrid nanoporous polystyrene derived from cubic octavinylsilsesquioxane and commercial polystyrene via the Friedel–Crafts reaction

Abstract

A series of hybrid nanoporous polystyrenes were synthesized from commercial polystyrene (PS) and cubic octavinylsilsesquioxane (OVS) via the Friedel–Crafts reaction. The porosity of the resulting hybrid polymers could be fine-tuned by varying the ratio of PS and OVS. The resulting polymers, HCP-1 to HCP-9 had apparent Brunauer–Emmett–Teller surface areas (S_BET) in a range of 2.6 to 767 m² g⁻¹, with total pore volumes in the range of 0.36 to 0.90 cm³ g⁻¹. The S_BET was maximum when OVS loading was 9.1 wt%; it then decreased to almost no porosity before increasing again with the increase of OVS loading. The thermal decomposition temperatures of the hybrid polymers were close to pure PS under a N₂ atmosphere, but the residues increased with the increase of OVS loading. The gas sorption applications revealed that HCP-3 possessed H₂ uptake of 3.01 mmol g⁻¹ (0.60 wt%) at 77 K and 1.01 bar and CO₂ uptake of 1.12 mmol g⁻¹ (4.93 wt%) at 298 K and 1.01 bar.

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Introduction

Porous materials with novel intrinsic properties such as high specific surface area, excellent porosity and good thermal stability have potential applications in gas storage and separation,¹ optical devices,^2,3 heterogeneous catalysis,^4,5 etc. Covalently-linked porous polymers have attracted specific interest because their structures and properties are easily tuned through rational design.⁶ Polystyrene is a general polymer that has been widely used. It possesses well-known properties, such as ease of processing and functionalization, solubility in a broad range of solvents, outstanding thermal stability, and mild substrate as supporter.⁷ As the first organic porous resin to be industrialized, hypercrosslinking polystyrene was prepared by the Davankov⁸ using the linear polystyrene, divinylbenzene and the lightly crosslinked gel-type styrene-divinylbenzene (St-DVB) copolymers as the raw materials, postfunctionalized with the highly cross-linking and porous structures via the Friedel–Crafts reaction. The hypercrosslinking polystyrene had been widely used as the sorbents adsorbing the organic solvents,^9,10 inorganic ions^11,12 and the gas,^13–15 and also used as the stationary phase in the column to separate the various materials¹⁶ due to its high porosities, lower density and excellent swelling properties. In addition, it had been used to prepare nanocomposites that exhibited excellent catalystic performance^17,18 and magnetic properties.¹⁹

Research on inorganic–organic hybrid nanocomposites has grown rapidly because of their advantages of the combination of flexibility, processability of organic polymers with the rigidity and thermal stability of the inorganic component.^20–22 Physically blending, interfacial interaction, in situ polymerization and other methods are used to prepare these hybrid nanocomposites, which exhibit excellent thermal and mechanical properties. Silica nanoparticles have exhibited a good thermal, chemical stability with well-defined, size-tunable structure. Thus grafting different functional organic layers onto the silica particles has been explored in many areas.^23–25 As a silica-like cage compound, polyhedral oligomeric silsesquioxane (POSS) provides an excellent platform for synthesis of new inorganic–organic hybrid materials with enhanced thermal and mechanical properties.²⁶ POSS has been incorporated into polystyrene via chemical grafting, including ATRP, RAFT, anion polymerization, Friedel–Crafts reaction etc., to form hybrid polystyrenes of various molecular architectures. These hybrid polystyrene based on POSS exhibited the improved thermal stabilities,^27,28 viscoelastic properties,^29,30 magnetic properties³¹ compared to the pristine polystyrene. In addition, nonreactive octaphenethyl POSS was also used to prepare hybrid nanocomposites with PS via physical blending. Results showed that the octaphenethyl POSS could be incorporated into polystyrene up to 40 wt% without phase separation.³²

The “bottom-up” topology combination has proved to be an efficient strategy to construct porous materials.^6,33 Rational selection of suitable rigid building blocks with different geometry will help to construct polymer networks with novel topology structures and properties. Linking the monomers with different geometries together can combine their advantages; in addition, the porosity and functionality of the resulting polymers could be easily tuned.^34,35 Rigid cage make POSS become an ideal building block to construct novel inorganic–organic hybrid porous materials. Some hybrid porous materials based on POSS have been synthesized by the reaction of other building blocks with different geometries.^36,37

Starting from cubic octavinylsilsesquioxane (OVS), we have successfully prepared some hybrid porous materials by the combination with planar benzene or tetrahedral tetraphenylsilane (TPS) via the Friedel–Crafts reaction and tuned their porosities by adjusting the ratio of OVS to benzene or TPS utilizing the multi-reaction sites of aromatic groups.^38,39 It was observed that S_BET increased with the increasing reactive sites of benzene, i.e. decreasing the ratio of benzene to OVS; however, the pore size distributions (PSDs) were wide and irregular and the pores changed from coexistent micro-mesopores to almost mesopores. The tunable porosity was correlated with the multi-reaction sites of benzene and thus diverse local cross-linking density in the networks formed by the Friedel–Crafts alkylation reaction.³⁸ Consistent with this report, when TPS was used as a crosslinker, S_BET was also monotonously enhanced with decreasing the ratio of TPS because of the increasing crosslinking density, which could lead to higher surface areas up to 989 m² g⁻¹. In comparison to benzene, TPS possessed a larger molecular volume and consisted of four phenyl groups, which could provide more connecting sites, acting as a concentrative crosslinker. Different from benzene as a crosslinker, the resulted porous materials exhibited uniform PSDs, i.e. microspores with an average diameter centered at about 1.5 nm and uniform mesopores with an average diameter centered at about 3.6 nm, which should be ascribed to the steric hindrance effect of TPS, making it more difficult to adjust its position during the reaction relative to benzene.³⁹

Covalently-linked porous polymers have been investigated widely, however most porous polymers arose from small building blocks.⁶ Using commercially available polymers as rigid building blocks to construct porous materials via simple modification is less reported by far. Owing to large rigid phenyl groups in polystyrene, it is possible to prepare hybrid porous polystyrenes through the topology combination with cubic OVS. Different from small aromatic molecules like benzene or TPS, it was expected that some novel porous materials could originate from the combination of polystyrene and OVS. More importantly, simple process and cheaper starting materials provide the possibility to economically prepare these porous materials in a large scale and make it possible to be industrialized.

In this paper, we attempt to use OVS to react with commercial linear polystyrene to prepare hybrid porous polymers via the Friedel–Crafts reaction. Their properties such as thermal properties, gas absorption and storage are also investigated. The resulting hybrid porous polymers exhibit high thermal stability, high porosity and high gas uptake ability in H₂ and CO₂.

To our knowledge, this is the first report on the preparation of porous materials from commercial polymer and POSS. The successful preparation of hybrid porous materials from commercial polystyrene and cubic OVS will stimulate more works on porous materials from other commercial polymers and POSS.

Experimental

Materials

The PS (M_n = 2.6 × 10⁵) was obtained from Aladdin-reagent limited Co., and used without further purification. OVS was prepared according to previous reports.⁴⁰ CS₂ was supplied by China National Medicines Group and purified using atmospheric distillation methods and stored with 4 Å molecule sieves prior to use.

Characterization

Fourier-transformed infrared (FT-IR) spectra were carried out using Bruker TENSOR27 infrared spectrophotometer from 400 to 4000 cm⁻¹ at a resolution of 4 cm⁻¹. The samples were prepared using conventional KBr disk method. Solid-state ¹³C 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 of 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 with π/2 pulse length of 5 μs, recycle delay of 120 s, and spinning rate of 5 kHz. Elemental analyses were conducted using Elementar vario EL III elemental analyzer.

Field-emission scanning electron microscopy (FE-SEM) experiments were characterized by a HITACHI S4800 spectrometer. Samples were dispersed in EtOH with the aid of sonication and a drop of ethanol suspension was loaded onto a crabon-coated copper grid and left to dry under infrared lamp; and the samples were coated by sputtering with a thin layer of Au prior to imaging. High-resolution transmission electron microscopy (HRTEM) experiments were recorded using a JEM 2100 electron microscope (JEOL, Japan) with an acceleration voltage of 200 kV. Samples were dispersed in EtOH with the aid of sonication, and a drop of ethanol suspension was loaded on the carbon-coated copper grid and was dried under the infrared lamp.

Thermal gravimetric analysis (TGA) was performed on a Mettler Toledo model SDTA 854 TGA system under N₂ atmosphere at a heating rate of 10 °C min⁻¹ from room temperature to 800 °C. Powder X-ray diffraction (PXRD) images were collected on a Riguku D/MAX 2550 diffractometer under Cu-Kα radiation, 40 kV, and 200 mA with a scanning rate of 10° min⁻¹.

N₂ sorption isotherm measurements were characterized by a Micro Meritics surface area and pore size analyzer. Before measurement, the samples were degassed for 12 h at 160 °C. A sample of ca. 100 mg and a UHP-grade N₂ (99.999%) gas source were adopted in the N₂ sorption measurements at 77 K and collected on a Quantachrome Quadrasorb apparatus. S_BET was confirmed over a P/P₀ range from 0.01 to 0.20. Nonlocal density functional theory (NL-DFT) pore size distributions (PSDs) were determined by C/slit-cylindrical pore mode of the Quadrawin software. CO₂ isotherms were measured at 298 K at 0.0 to 1.01 bar. H₂ adsorption capacity was measured at 77 K at 0.0 to 1.01 bar. Before measurement, the samples were degassed at 150 °C under vacuum for about 15 h.

Preparation of the hybrid polymers (HCPs)

Ar charged with polystyrene (1.00 g, 3.85 × 10⁻² mmol), catalytic amount of anhydrous AlCl₃, stoichiometric OVS (Table 1) and CS₂ (10 mL) were placed in an oven-dried flask. The resulting mixture was vigorously stirred at room temperature for 0.5 h and under reflux for 24 h. Then the mixture was cooled to room temperature. For HCP-1 to HCP-2, the mixture was precipitated in ethanol and dried in vacuo at 60 °C for 48 h. For HCP-3 to HCP-9, the mixture was filtered and washed with ethanol, acetone, water, and tetrahydrofuran. The slightly pink products were obtained under the Soxhlet extractor with dichloromethane for 48 h, and dried in vacuo at 60 °C for 48 h.

Table 1 Composition of the starting materials for HCP-1 to HCP-9

Sample	PS (mmol)	OVS (mmol)	OVS (wt%)	Mvinyl/Mphenyl^a
a The molar ratio of the vinyl groups to the phenyl groups.
HCP-1	3.85 × 10^−2	6.32 × 10^−2	3.8	0.052
HCP-2	3.85 × 10^−2	1.26 × 10^−1	7.4	0.10
HCP-3	3.85 × 10^−2	1.58 × 10^−1	9.1	0.13
HCP-4	3.85 × 10^−2	3.16 × 10^−1	16.7	0.26
HCP-5	3.85 × 10^−2	4.74 × 10^−1	23.1	0.39
HCP-6	3.85 × 10^−2	6.32 × 10^−1	28.6	0.53
HCP-7	3.85 × 10^−2	9.48 × 10^−1	37.5	0.79
HCP-8	3.85 × 10^−2	12.64 × 10^−1	44.4	1.1
HCP-9	3.85 × 10^−2	15.8 × 10^−1	50.0	1.3

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Results and discussion

As shown in Scheme 1, hybrid porous polymers were synthesized through the Friedel–Crafts reaction of OVS with stoichiometric PS in CS₂ under reflux for 24 h. For HCP-1 and HCP-2, they still dissolved in CS₂ and other solvents, for example, tetrahydrofuran, dichloromethane. For HCP-3 to HCP-9, the products were highly crosslinked and did not dissolve in CS₂ and other solvents. The content of carbon and hydrogen of HCPs was confirmed by elemental analysis, and the results were provided in the ESI (S1‡).

Scheme 1 Synthetic routes for HCPs, and possible fragments A and B.

These hybrid polymers were first characterized by FT-IR spectra and the spectra of HCP-3, HCP-4 and HCP-8, HCP-9 were shown in Fig. 1. The spectra of HCP-1, HCP-2, HCP-5, HCP-6 and HCP-7 were supported in the ESI (S2–S6‡). Compared with the FT-IR pattern of OVS, the intensities of the peaks at 1603 and 1410 cm⁻¹ decreased, which was associated with vinyl groups⁴¹ of HCP-3 to HCP-9, indicating that the polymerization reaction occurred. The peaks between 3080 and 2843 cm⁻¹ could be assigned to C–H stretching vibration of aromatic, vinyl, methyl and methylene groups. The strong peak at ∼1113 cm⁻¹ was attributed to typical Si–O–Si stretching vibrations, and the results proved that cubic silsesquioxane cages existed in these hybrid porous materials.^42–44

Fig. 1 FT-IR of the OVS, PS, HCP-3, HCP-4 and HCP-8, HCP-9.

The chemical structures of these hybrid polymers were also determined by the solid-state ¹³C CP/MAS NMR and ²⁹Si MAS NMR spectroscopy. Owing to their similar solid ¹³C CP/MAS NMR and ²⁹Si MAS NMR spectra for these hybrid polymers, HCP-3 was selected as a representative example to analyze. The solid-state ¹³C CP/MAS NMR spectrum of HCP-3 was displayed in Fig. 2a. The resonance peaks in the range of 128 to 142.6 ppm were ascribed to the carbon atoms derived from the bridging aromatic units and the unreacted Si–CH=CH₂. The resonance peak at the 28.8 ppm was attributed to the β C atoms at the linker units of –Si–CH₂–CH₂– formed after the Friedel–Crafts reaction. The resonance peak at the 13.8 ppm was attributed to the α C atoms at the linker units of –Si–CH₂–CH₂– formed after the Friedel–Crafts reaction and thus results further confirmed the success of the cross-linking reaction. The solid-state ²⁹Si MAS NMR spectrum of the HCP-3 (Fig. 2b) showed that the resonance peaks at the −67 and −80 ppm could be ascribed to the silicon atoms of T₃ units (T_n: CSi(OSi)_n(OH)_3−n) from the Si–CH₂–CH₂– units formed after the Friedel–Crafts reaction and the unreacted Si–CH=CH₂ units, respectively. Compared with other POSS-based porous polymers,^37,44 no T₁ or T₂ unit was observed, suggesting that no POSS cage collapsed in the frameworks during synthesis, which was consistent with our previous report.³⁸ The two peaks at ∼−5 ppm and ∼−130 ppm were two reference peaks.

Fig. 2 (a) Solid-state ¹³C MAS NMR spectrum of HCP-3. (b) Solid-state ²⁹Si MAS NMR spectrum of HCP-3.

The porous structure of HCPs was investigated by N₂ adsorption-desorption analysis at 77 K. The N₂ isotherms showed that HCP-1, HCP-2, HCP-5, HCP-6 and HCP-7 had the nominal surface area of 2.6, 2.6, 38, 12 and 41 m² g⁻¹, respectively. The results indicated that there was almost no pore in these hybrid polymers. The other N₂ isotherms of HCP-3, HCP-4, HCP-8 and HCP-9 were shown in the Fig. 3. Four hybrid polymers exhibited a combination of type I and type IV N₂ gas sorption isotherms according to IUPAC classifications and were consistent with the previous reports. The isotherms of HCP-3, HCP-4, HCP-8 and HCP-9 show a steep nitrogen gas uptake at low relative pressure (P/P₀ < 0.001), reflecting that there existed some amounts of micropores in the networks structure, and there is gradually increasing gas uptake at higher relative pressures (P/P₀ > 0.5) with a clear hysteresis, indicating that these materials contained mesopores.⁴⁵ Besides, the gas uptake isotherm of HCP-3 was slightly steeper than other three isotherms at higher relative pressures, which suggested that the contribution of mesopores in the HCP-3 was higher than the HCP-4, HCP-8 and HCP-9. The detailed porosity data of these polymers were shown in Table 2. The apparent BET specific surface areas (S_BET) of HCP-3, HCP-4, HCP-8 and HCP-9 were 767, 509, 473, and 582 m² g⁻¹, respectively. The total pore volumes (V_TOTAL) of the networks were 0.90, 0.36, 0.40 and 0.49 cm³ g⁻¹ calculated at P/P₀ = 0.99, respectively. The S_BET of hybrid polymers firstly increased up to a maximum value, subsequently decreased before increasing with the increase of OVS loading. S_BET of hybrid polymer was maximum when OVS loading was 9.1 wt%; when OVS loading was 3.8, 7.4, 23.1, 28.6, 37.5 wt%, respectively, there was no porosity for HCP-1, HCP-2, HCP-5, HCP-6 and HCP-7.

Fig. 3 N₂ sorption isotherms of the HCP-3, HCP-4, HCP-8 and HCP-9.

Table 2 Porosity data of HCP-1 to HCP-9

Sample	SBET^a/m^2 g^−1	Smicro^b/m^2 g^−1	Vtotal^c/cm^3 g^−1	Vmicro^d/cm^3 g^−1	Vmicro/Vtotal
a Surface area calculated from N2 adsorption isotherm using 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 t-plot method based on the Halsey thickness equation.
HCP-1	2.6
HCP-2	2.6
HCP-3	767	154	0.90	0.06	0.07
HCP-4	509	169	0.36	0.08	0.22
HCP-5	38
HCP-6	12
HCP-7	41
HCP-8	473	128	0.40	0.06	0.15
HCP-9	582	208	0.49	0.09	0.18

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The pore size distributions (PSDs) of these hybrid hypercrosslinking polystyrenes were calculated by nonlocal density functional theory (NL-DFT), and the results were displayed in Fig. 4. HCP-3 possessed relatively uniform micropores with an average diameter centered at 1.4 nm and a broader distribution of mesopores from 2.2 to 14.5 nm. HCP-4, HCP-8 and HCP-9 also displayed uniform micropores with an average diameter centered at 1.4 nm and a narrower distribution of mesopores from 2.2 nm to 4.4 nm compared with HCP-3. The PSD results were consistent with the shape of N₂ isotherms, indicating that micropores and mesopores coexisted in the hybrid polymers.

Fig. 4 NL-DFT PDS of the HCP-3, HCP-4, HCP-8 and HCP-9.

There are several factors to explain the variation in the surface area and pores size distribution of these hybrid polymers. According to the previous reports, traditional hypercrosslinking porous polystyrenes were prepared by the precursor of linear polystyrene through adding small molecule of divinyl benzene as a crosslinking agent via the Friedel–Crafts alkylation reaction.⁴⁶ During the process, initial polystyrene coils, a cross-agent and a Friedel–Crafts catalyst were homogeneously distributed throughout the whole volume of their solution in ethylene dichloride. The polymeric chains extended through the whole initial solution (or gel) and remained strongly solvated over all period of network formation. Intra- and intermolecular cross-linking simultaneously emerged throughout the entire volume of the reacting system. Therefore, the pores in the structures were constructed by the aggregation of the polymer chains. The homogeneous cross-linking structures and high degree of cross-linking densities could be obtained in these polymers structures due to the small volumes and the less steric hindrance as well as the high reactivity of small molecules in presence of the catalyst. S_BET and the cross-linking densities of these polymers increased with the increasing amount of the cross-linking agents. However, in this report, bulky OVS was used as a crosslinker in the polymerization system. Rigid cage and multifunctionality make OVS quite different from small molecule cross-linkers, such as divinybenzene, monochlorodimethyl ether and dimethyl formal.^47,48 Eight vinyl groups in one cage make it act as a concentrative crosslinker in the Friedel–Crafts reaction.³⁹ The rigid cage makes it a potential nanobuilding block to form porous materials via the stacking of POSS cages.

Both OVS and PS could act as the host building blocks to construct porous materials in this study. It is therefore interesting to study the effect of the host–guest exchange of the two building blocks on the porosities of the resulting porous polymer networks by changing the ratio of PS and OVS. When OVS loading was lower than 9.1 wt% in this study, the resulting hybrid polystyrenes, i.e. HCP-1 and HP-2, were slightly crosslinked and dissolved in most common solvents, for example, THF, chloroform etc. The resulting hybrid polystyrenes could not stack to form pores and exhibited no porosity by the BET measurements due to the lower crosslinking density.

When OVS loading was 9.1 wt% (i.e. HCP-3), a highly crosslinking network was formed, which favoured formation of pores and the resulting hybrid polystyrene did not dissolve in the common solvents and exhibited a maximum S_BET of 767 m² g⁻¹. The pores in the networks were assigned to the aggregation of the polystyrene chains, in which OVS acted as a concentrative linker. Thereby, the local cross-linking density was higher, which resulted in high apparent specific surface. Meanwhile, the cross-linking density was inhomogeneous because of the relatively lower loading of the OVS. Consequently, the broader PSD was obtained. The structure of fragment A might be predominant in the resulting hybrid network when PS acted as the host building block (Scheme 1).

With further increasing OVS loading, on the one hand, most of vinyl groups might crosslink polystyrene, which generated more crosslinking points, the cross-linking density and the crosslinking homogeneity increased. The results lead to higher specific surface area and narrower PSD. Nonetheless, the number of the unreacted vinyl groups increased because of the steric effect of OVS, which had been confirmed by the FT-IR spectra. This resulted in the high free volumes of the networks, which decrease the S_BET of the hybrid polymers.⁴⁴ In addition, the framework interpenetration⁴⁵ might form due to the average crosslinking density between OVS and PS and resulted in the pore-filling in the networks, which decreased the apparent specific area of the networks. As a comprehensive result of these factors on porosity, S_BET decreased for HCP-4, HCP-5, HCP-6 and HCP-7 till no porosities.

When OVS loading was higher than 44.4 wt%, the obtained hybrid networks exhibited higher porosity again, for example, HCP-8 and HCP-9. For these hybrid materials, OVS acted as the host and these porosities arose from the stack of POSS cages in which, polystyrene act as a concentrative crosslinker. The structure of fragment B might dominate in the resulting hybrid crosslinking networks when OVS acted as the host (Scheme 1).

To evaluate the thermal stability of hypercrosslinking polymers, TGA was performed under N₂ at 10 min⁻¹ from room temperature to 800 °C. The results were shown in the Fig. 5. Consistent with the previous reports,^38,49 the initial decomposition temperatures of OVS and PS were about 250 and 370 °C, respectively. Compared with pure PS, the decomposition temperatures of HCP-3 to HCP-9 were relatively similar and close to the pure PS. However, the residues of HCP-3 to HCP-9 at the 800 °C increased with the increase of OVS loading.

Fig. 5 TGA curves of OVS, PS and HCP-3 to HCP-9.

As expected, these hybrid polymers were amorphous and exhibited no long-range crystallographic order as revealed by powder X-ray diffraction (PXRD) (Fig. 6). This result was similar to other nanoporous hybrid POSS-based materials. The HCP-3 to HCP-9 exhibited broad diffraction peaks at 2θ of ∼22°, which was typically observed in amorphous silica nanocomposites and associated with the Si–O–Si linkages.³⁷ The particle size and internal morphologies of the polymers were characterized by the FE-SEM. In view of the similarity of the morphologies for these HPPs, HCP-3 was selected as a representative sample. The others images were displayed in the ESI (Fig. S7–S19‡). As shown in Fig. 7a, the structure consisted of interlinking irregular shapes with nanostructure appearance and a wide range of diameters from 100 nm to tens of micrometers. All the samples were constructed by great amount of irregular particles with a wide range of size distribution ranging from 100 nm to several tens of micrometers. In order to further characterize the texture and ordering of these materials, high-resolution transmission electron microscopy (HR-TEM) was performed. The HCP-3 image (Fig. 7b) revealed that the polymer exhibited the features of amorphous porous materials without long-range ordering. The samples were stable under the electron beam.

Fig. 6 The XRD patterns of OVS and HCP-3 to HCP-9.

Fig. 7 (a) SEM image of HPP-3 and (b) HRTEM image of HPP-3.

Gas storage is one of the important and promising applications of porous materials,⁵⁰ In order to evaluate the gas storage performances of the obtained hybrid hypercrosslinking polymers, H₂ and CO₂ sorption experiments at 77 and 298 K were performed. Compared with the HCP-4, HCP-8 and HCP-9, HCP-3 possessed the highest surface area and pore volume. It was selected as an example to evaluate the H₂ and CO₂ sorption properties. The H₂ storage capacity for HCP-3 was 3.01 mmol g⁻¹ (0.60 wt%) at 1.01 bar, 77 K (Fig. 8a). The CO₂ uptake for HCP-3 was 1.12 mmol g⁻¹ (4.93 wt%) at 1.01 bar, 298 K (Fig. 8b). The adsorption capacities were comparable to those of other porous polymers with similar surface areas. For example, Germain et al.¹⁴ reported that the Amberlite XAD16 with a S_BET of 770 m² g⁻¹ exhibited a H₂ storage uptake of 0.6 wt% at 77.3 K and 0.12 MPa; the Amberlite XAD16 was constructed from styrene and divinylbenzene building blocks. Dawson et al.⁵¹ reported that the CMP-1 with a S_BET of 839 m² g⁻¹ exhibited a CO₂ storage uptake of 1.18 mmol g-1 at 298 K and 1 bar; CMP-1 was constructed from 1,3,5-triethynylbenzene and 2,5-dibromobenzene via Sonogashira–Hagihara palladium catalyzed cross-coupling reaction. These values suggested that HPPs could be considered as promising candidates for H₂ and CO₂ storage.

Fig. 8 Gas sorption isotherms of HCP-3. (a) H₂ adsorption isotherm at 77 K. (b) CO₂ adsorption isotherm at 298 K.

Conclusions

In conclusion, octavinylsilsesquioxane (OVS) reacted with commercial polystyrene to prepare hybrid porous hypercrosslinking polymers via the Friedel–Crafts alkylation through the ingenious design. The porosity can be fine-tuned by changing the ratio of PS to OVS. The resulting polymers HCP-1 to HCP-9 with the apparent Brunauer–Emmett–Teller surface areas (S_BET) were in a range of 2.6 to 767 m² g⁻¹, with total pore volumes in the range of 0.36 to 0.90 cm³ g⁻¹. The gas sorption applications revealed that HCP-3 possessed H₂ uptake of 3.01 mmol g⁻¹ (0.60 wt%) at 77 K and 1.01 bar and CO₂ uptake of 1.12 mmol g⁻¹ (4.93 wt%) at 298 K and 1.01 bar, which demonstrated that these materials had the potential to be applied in gas storage of H₂ and CO₂.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (21274081).

Notes and references

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Footnotes

† We dedicate this paper to Prof. Hongzhi Liu's mother, who is dearly missed by all members of the family.

‡ Electronic supplementary information (ESI) available: The elemental analysis results of HCP-1 to HCP-9; FT-IR spectra of HCP-1, HCP-2, HCP-5 to HCP-7; FE-SEM images of HCP-3 to HCP-9 with different magnifications and areas. See DOI: 10.1039/c4ra14830d

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