| Low-density porous polymeric materials have received considerable attentions during the past few years owing to their abundant pore structure and high specific surface area.There are several templating methods that can be used for the preparation of porous polymers,including block copolymer templating and gel emulsion templating.The block copolymer templating can be used to generate mesoporous polymers and the pore size varies from 2 to 50 nm.However,the template is much more difficult to be removed,which tremendously limited the practical application of these polymeric materials.While the gel emulsion templating can be used to generate hierarchical porous materials,and their characteristic pore size can range from a few nanometers to hundreds of micrometers.What’s more,the internal structures of these materials could be largely adjusted.Therefore,these microporous polymeric materials are widely used in gas adsorption,oil-water separation,catalyst carriers,cell culture and so on.Gel-emulsions are two-phase gel-like systems,which usually consist of stabilizer,continuous phase and dispersed phase.It is generally recommended that the volume fraction of the dispersed phase of gel-emulsion is greater than 74%(the value is the critical volume fraction of the least cumulative variable spheres),and the obtained gel-emulsion has a typical foam-like structure and viscoelastic rheological behaviour.Stabilizer is the key factor for the formation of gel emulsion.The stabilizers of the traditional gel emulsions mainly include surfactants and micro-/nano-particles.For the former one,the addition is much larger(5%～50%,w/v),consequently,it is difficult to be removed from the generated monoliths,which may cause secondary pollution.For the latter one,the obtained gel emulsion is easy to be phase inversed when the volume fraction of the dispersed phase reaches nearly 74%.Faced with these problems,our group proposed that Low-Molecular-Mass Gelators(LMMGS)as a novel stabilizer to prepare the gel emulsions,which effectively solved the aforementioned prominent problems.Compared with the traditional surfactants or micro/nano-particles,LMMGs have obvious advantages.For example,the addition of the stabilizer is-2%(w/v,accounts for the continuous phase),and the volume fraction of dispersed phase is not subject to the limitation of 74%.This is due to the formation of gel emulsions relys on weak interaction forces,which makes solvents in the system almost illiquid and water droplets difficult to gather or phase separate,thus stable gel emulsions are obtained.Generally,traditional gel emulsions are mostly liquid/liquid systems,however,gel emulsions stabilized by LMMGs are liquid/gel and even gel/gel systems.It is the special system that makes the volume fraction of dispersed phase in gel emulsions less than 74%possible.That is the bases for porous polymeic materials preparation using gel emulsions as templating,and the fine control of the internal pore structures,shape and density of the porous materials.In addition,the drying process of porous materials prepared using LMMGs as a stabilizer does not need supercritical CO2 drying,freeze drying and other high-energy consumption process,only some appropriate washing and room temperature drying are needed.Therefore it is convinent for large-scale industrial production.Based on the structure characteristics of LMMGs,the water-in-oil(W/O)type gel emulsions were used as template to generate hierarchical porous materials.We synthesized the polymerizable cholesterol derivatives,a derivative of poly(oligo)-dimethylsiloxane with two olefinic bonds at its ends(D-PDMS)and a polymerizable star-shaped compound,respectively,as the continuous phase,instead of commonly used benzene-containing polymeric units.The three prepared compounds act as stabilizers,polymeric monomers as well as cross-linkers.In addiation,the gelation behavior,gel emulsion formation property and template-preparation of low-density porous materials of them were studied.What’s more,we developed two types of flexible,compressible and low-density porous materials for volatile organic compounds(VOCs)adsorption.The research work of this dissertation mainly includes the following two aspects.Part one,a polymerizable cholesteryl derivative(CEA)was designed,which utilized as the LMMGs and polymeric monomer.The gelation behaviors of CEA in six polymeric monomers and thirty solvents were investigated.The results of gelation test indicate that CEA could gel long chain saturated hydrocarbons such as n-heptane.A stable water-in-oil(W/O)type gel emulsion was prepared using CEA as the stabilizer,the mixture of toluene and n-heptane as the continuous phase and water as the dispersed phase.In addition,a derivative of poly(oligo)-dimethylsiloxane with two olefinic bonds at its ends(D-PDMS)was also purposely prepared and employed as a cross-linker,and little hydrophobic fumed silica as the thickening agent.As expected,polymerization of the continuous phase resulted in porous polymeric monoliths.Interestingly,the internal structures of the materials could be largely adjusted via simple variation of the ratio of n-heptane to toluene in the continuous phase.Moreover,utilization of the specially synthesized cross-linker endows the monoliths flexibility,which must bring convenience for real-life applications.Adsorption test demonstrated that the porous materials are good adsorbents for formaldehyde(～1,300 mg/g)and toluene(～900 mg/g)at ambient conditions,and they are re-usable after simple washing and drying.Considering the simple preparation method including ambient pressure drying without solvent exchange,the superior performance in the adsorption tests,and the fact that the as created CEA could function both as a monomer and a stabilizer,it is believed that the work presented represents a substantial progress of the techniques used for preparation of porous polymeric materials,and has huge application prospects for adsorption of toxic formaldehyde and toluene from contaminated air.Part two,a polymerizable star-shaped compound named as BTN was designed and synthesized.We investigated the gelation behaviors of BTN in six polymeric monomers and thirty solvents,indicating BTN could gel aromatic hydrocarbon derivatives such as benzene and toluene.Based upon the above findings,stable gel-emulsions with the mixture of toluene,BTN,D-PDMS and silane agents as the continuous phase and water as the dispersed phase were prepared.As expected,polymerization of the continuousphase resulted in porous polymeric monoliths,and the introduction of D-PDMS and silane agents into the as-prepared gel-emulsions improved the compressibility of monoliths,for example,50 successive cycles of compression with 70%strain tests showed no changes in the appearance.More importantly,the polymeric monoliths can be used to adsorb the aromatic hydrocarbons derivatives from air.Adsorption test demonstrated that the porous materials are outstanding adsorbents for styrene(-580 mg/g),aniline(～1,000 mg/g)and toluene(～1,300 mg/g)at ambient conditions,and they are re-usable after simple washing and drying,which showed the prominent economical and environmental friendly character.It can be believed that the porous polymeric materials in the volatile gas adsorption of aromatic derivative has potential application value. |
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