Compressible and monolithic microporous polymer sponges prepared via one-pot synthesis

Abstract

Compressible and monolithic microporous polymers (MPs) are reported. MPs were prepared as monoliths via a Sonogashira-Hagihara coupling reaction of 1,3,5-triethynylbenzene (TEB) with the bis(bromothiophene) monomer (PBT-Br). The polymers were reversibly compressible, and were easily cut into any form using a knife. Microscopy studies on the MPs revealed that the polymers had tubular microstructures, resembling those often found in marine sponges. Under compression, elastic buckling of the tube bundles was observed using an optical microscope. MP-0.8, which was synthesized using a 0.8:1 molar ratio of PBT-Br to TEB, showed microporosity with a BET surface area as high as 463 m(2)g(-1). The polymer was very hydrophobic, with a water contact angle of 145° and absorbed 7-17 times its own weight of organic liquids. The absorbates were released by simple compression, allowing recyclable use of the polymer. MPs are potential precursors of structured carbon materials; for example, a partially graphitic material was obtained by pyrolysis of MP-0.8, which showed a similar tubular structure to that of MP-0.8.

Figure 1. Reaction scheme for the synthesis of the bis(bromothiophene) monomer (PBT-Br) and microporous polymers (MPs).

The polymers were prepared by a Sonogashira-Hagihara coupling reaction.

Figure 2. Electron microscope images of MPs.

(a–c) SEM images of MP-0.8 (scale bar: a = 100 μm, b = 10 μm, and c = 5 μm). (d–f) TEM images of MP-0.8 (scale bar: d = 500 nm, e = 1 μm, and f = 1 μm). SEM images of (g) MP-1.0 (scale bar = 100 μm), (h) MP-1.2 (scale bar = 20 μm), and (i) MP-1.5 (scale bar = 10 μm).

Figure 3. Monolithic and compressible properties of MP-0.8.

(a) Images of MP-0.8 prepared in a 10 mL vial as a mold (upper) and of the polymer cut into a star shape (lower). (b) Images of MP-0.8 under loaded and unloaded conditions (scale bar = 5 mm). (c) Compressive stress–strain curves of MP-0.8 for the first and tenth test cycles.

Figure 4. Effect of the reaction time on MP-0.8.

(a) Time-dependent images of a reaction mixture of PBT-Br and TEB (molar ratio = 0.8:1) in toluene/DMF (1:1, v/v) on a hotplate. (b) Strain–stress curves of the samples obtained after different reaction times. SEM images of the samples obtained after a reaction time of (c) 10 min and (d) 3 h (scale bars = 40 μm). (e) SEM image of MP-lin (scale bar = 40 μm).

Figure 5. Mechanism of the compressibility of MP-0.8.

(a) Optical microscope images of MP-0.8 taken under loaded and unloaded conditions (scale bar = 50 μm). (b) Schematic drawing of the mechanism of the compressibility of MP-0.8.

Figure 6. Hydrophobicity and absorption properties of MP-0.8.

(a) The water contact angle measured on the surface of MP-0.8. (b) A droplet of water dyed with Rhodamine B on the surface of MP-0.8. (c) Removal of n-decane dyed with Oil Red O floating on water using MP-0.8. (d) Release of absorbed n-decane by compression and repeated absorption using MP-0.8. (e) Absorption capacity of MP-0.8 for various liquids, and (f) their correlation with the absorbate density.

Figure 7. Efficient dye removal using MP-0.8.

(a) UV–Vis spectra of Sudan I solutions (initial concentration = 5.0 × 10^–5 M in ethanol) measured after removing a dye by MP-0.8 (0, 25, 50, 75, and 100 cycles of compression and release, and a static absorption for 10 min) and by a urethane sponge (100 cycles of compression and release) (black circles). (b) Photographs of the above solutions. (c) UV–Vis spectra of the Sudan I stock solution and a filtered solution. (d) Sequential photographs showing Sudan I dye capture using an MP-0.8 syringe filter.

Figure 8. Carbonization of MP-0.8.

(a) SEM image (scale bar = 2 μm) and (b) Raman spectrum of MP-0.8-C. (c) N₂ adsorption–desorption isotherms of MP-0.8-C measured at 77 K. (d) NL-DFT pore size distribution of MP-0.8-C.