氣體分離膜的交聯(lián)處理研究文獻(xiàn)綜述塑化是聚合物膜商品化的一個(gè)巨大障礙，對(duì)聚合物膜進(jìn)行交聯(lián)處理是目前被認(rèn)為改善這一問(wèn)題的有效方法。交聯(lián)處理一般包括化學(xué)交聯(lián)、UV交聯(lián)和熱誘導(dǎo)交聯(lián)等方式。這些交聯(lián)處理的目的是為了使聚合物鏈與鏈之間變得更加緊密，形成的交聯(lián)網(wǎng)狀結(jié)構(gòu)可以使膜的內(nèi)部結(jié)構(gòu)更加穩(wěn)定，能夠在高壓條件下防止高度可溶的氣體把膜材料溶脹或塑化。化學(xué)交聯(lián)圖1-36FDA-durene與線(xiàn)性二胺分子的化學(xué)交聯(lián)機(jī)理Fig.1-3Thechemicalcross-linkingmechanismof6FDA-dureneandlineardiaminemolecules化學(xué)交聯(lián)一般是選用二胺或二醇等小分子作為交聯(lián)劑，可以對(duì)含有羥基、羧基和氨基等官能團(tuán)的聚合物進(jìn)行化學(xué)反應(yīng)交聯(lián)。這種交聯(lián)反應(yīng)的優(yōu)勢(shì)是不僅可以在聚合物膜中形成網(wǎng)狀結(jié)構(gòu)優(yōu)化膜內(nèi)的鏈間距，而且還可以在交聯(lián)結(jié)構(gòu)中引入氫鍵改善聚合物的化學(xué)環(huán)境。Chung課題組采用化學(xué)交聯(lián)的方式對(duì)聚酰亞胺氣體分離膜進(jìn)行改性處理[[]CAOC,CHUNGTS,LIUY,etal.Chemicalcross-linkingmodificationof6FDA-2,6-DAThollowfibermembranesfornaturalgasseparation[J].JournalofMembraneScience,2003,216(1-2):257-268.,[]LIUY,WANGR,CHUNGTS.Chemicalcross-linkingmodificationofpolyimidemembranesforgasseparation[J].JournalofMembraneScience,2001,189(2)[]CAOC,CHUNGTS,LIUY,etal.Chemicalcross-linkingmodificationof6FDA-2,6-DAThollowfibermembranesfornaturalgasseparation[J].JournalofMembraneScience,2003,216(1-2):257-268.[]LIUY,WANGR,CHUNGTS.Chemicalcross-linkingmodificationofpolyimidemembranesforgasseparation[J].JournalofMembraneScience,2001,189(2):231-239.[]CHUNGTS,SHAOL,TINPS.SurfaceModificationofPolyimideMembranesbyDiaminesforH2andCO2Separation[J].MacromolecularRapidCommunication,2006,27(13):998-1003.圖1-4含羧基聚合物與線(xiàn)性二醇分子的交聯(lián)機(jī)理Fig.1-4Themechanismofchemicalcross-linkingbetweencarboxyl-containingpolymersandlineardihydroxymoleculesKoros課題組使用乙二醇作為交聯(lián)劑對(duì)6FDA-mPD/DABA聚酰亞胺進(jìn)行交聯(lián)[[]STAUDT-BICKELC,KOROSWJ.ImprovementofCO2/CH4separationcharacteristicsofpolyimidesbychemicalcrosslinking[J].JournalofMembraneScience,1999,155(1):145-154.]，由于DABA含有強(qiáng)極性的羧酸基團(tuán)可以與乙二醇發(fā)生化學(xué)反應(yīng)，降低聚合物鏈的遷移率，交聯(lián)聚合物膜具有良好的抗塑化性能。該組還通過(guò)丙二醇作為交聯(lián)劑處理中空纖維氣體分離膜[[][]STAUDT-BICKELC,KOROSWJ.ImprovementofCO2/CH4separationcharacteristicsofpolyimidesbychemicalcrosslinking[J].JournalofMembraneScience,1999,155(1):145-154.[]KRATOCHVILAM,KOROSWJ.EffectsofSupercriticalCO2ConditioningonCross-LinkedPolyimideMembrane[J].Macromolecules,2010,43(10):4679-4687.[]MAC,KOROSWJ.EffectsofhydrocarbonandwaterimpuritiesonCO2/CH4separationperformanceofester-crosslinkedhollowfibermembranes[J].JournalofMembraneScience,2014,451:1-9.[]DUN,CINMD,PINNAUI,etal.Azide-basedcross-linkingofpolymersofintrinsicmicroporosity(PIMs)forcondensablegasseparation[J].Macromolecularrapidcommunications,2011,32(8):631-636.UV輻射交聯(lián)UV交聯(lián)是指通過(guò)紫外線(xiàn)照射使聚合物鏈在某些化學(xué)鍵處出現(xiàn)了裂解產(chǎn)生自由基，在光化學(xué)反應(yīng)下發(fā)生重排交聯(lián)的反應(yīng)。Kita等發(fā)現(xiàn)能夠通過(guò)改變照射時(shí)間來(lái)調(diào)節(jié)膜材料的氣體滲透性能[[]KITAH,INADAT,TANAKAK,etal.Effectofphotocrosslinkingonpermeabilityandpermselectivityofgasesthroughbenzophenone-containingpolyimide[J].JournalofMembraneScience,1994,87(1):139-147.]，膜的選擇性隨著照射時(shí)間的增加而不斷升高，但是由于鏈間距的減小會(huì)使膜的滲透性不斷降低。Paul等通過(guò)UV照射對(duì)聚芳酯進(jìn)行處理[[]MCCAIGMS,PAULDR.EffectofUVcrosslinkingandphysicalagingonthegaspermeabilityofthinglassypolyarylatefilms[J].Polymer,1999,40(26):7209-7225.[]KITAH,INADAT,TANAKAK,etal.Effectofphotocrosslinkingonpermeabilityandpermselectivityofgasesthroughbenzophenone-containingpolyimide[J].JournalofMembraneScience,1994,87(1):139-147.[]MCCAIGMS,PAULDR.EffectofUVcrosslinkingandphysicalagingonthegaspermeabilityofthinglassypolyarylatefilms[J].Polymer,1999,40(26):7209-7225.[]ROSUL,SAVAI,ROSUD.Modificationofthesurfacepropertiesofapolyimidefilmduringirradiationwithpolychromiclight[J].AppliedSurfaceScience,2011,257(15):6996-7002.[]LIFY,XIAOYC,ONGYK,etal.UV-rearrangedPIM-1Polymericmembraneforadvancedhydrogenpurificationandproduction[J].AdvancedEnergyMaterials,2012,2(12):1-11.圖1-5PIM-1膜光化學(xué)反應(yīng)的機(jī)理Fig.1-5MechanismofthephotochemicalreactionofPIM-1membranes熱誘導(dǎo)交聯(lián)熱誘導(dǎo)交聯(lián)是指通過(guò)高溫驅(qū)使聚合物鏈上的一些化學(xué)鍵出現(xiàn)了斷裂產(chǎn)生了自由基，自由基之間形成交聯(lián)結(jié)構(gòu)[[]CHUAML,XIAOYC,CHUNGTS.Effectsofthermallylabilesaccharideunitsonthegasseparationperformanceofhighlypermeablepolyimidemembranes[J].JournalofMembraneScience,2012,415:375-382.]。通常交聯(lián)改性的聚合膜有著良好的選擇性、耐化學(xué)性和耐塑化性[[]ZHANGCL,LIP,CAOB.DecarboxylationcrosslinkingofpolyimideswithhighCO2/CH4separationperformanceandplasticizationresistance[J].JournalofMembraneScience,2017,528:206-216.,[][]CHUAML,XIAOYC,CHUNGTS.Effectsofthermallylabilesaccharideunitsonthegasseparationperformanceofhighlypermeablepolyimidemembranes[J].JournalofMembraneScience,2012,415:375-382.[]ZHANGCL,LIP,CAOB.DecarboxylationcrosslinkingofpolyimideswithhighCO2/CH4separationperformanceandplasticizationresistance[J].JournalofMembraneScience,2017,528:206-216.[]KRATOCHVILAM,KOROSWJ.Decarboxylation-InducedCross-LinkingofaPolyimideforEnhancedCO2PlasticizationResistance[J].Macromolecules,2016,41(21):7920-7927.圖1-6從聚酰亞胺、環(huán)糊精接枝的聚酰亞胺到熱交聯(lián)的環(huán)糊精接枝的聚酰亞胺的演變過(guò)程。Fig.1-6TheevolutionschemefrompolyimideandcyclodextringraftedpolyimidetothermallycrosslinkedcyclodextringraftedpolyimideChung等將環(huán)糊精接枝在帶有羧基側(cè)基的高剛性聚酰亞胺上[[]XIAOY,CHUNGTS.Graftingthermallylabilemoleculesoncross-linkablepolyimidetodesignmembranematerialsfornaturalgaspurificationandCO2capture[J].Energy&EnvironmentalScience,2011,4(1):201.][]XIAOY,CHUNGTS.Graftingthermallylabilemoleculesoncross-linkablepolyimidetodesignmembranematerialsfornaturalgaspurificationandCO2capture[J].Energy&EnvironmentalScience,2011,4(1):201.[]ANH,LEEAS,KAMMAKAKAMI,etal.Bromination/Debromination-InducedThermalCrosslinkingof6FDA-DureneforAggressiveGasSeparations[J].JournalofMembraneScience,2017,545:358-366.在熱誘導(dǎo)處理聚合物膜的過(guò)程中，當(dāng)熱處理溫度高于Tg時(shí)，容易導(dǎo)致基于這種材料的中空纖維膜的孔結(jié)構(gòu)和過(guò)渡層塌陷。為了解決這一難題，最有效的方法是增加聚合物的Tg。Koros等合成了6FDA-DAM:DABA聚合物（Tg=387℃）[[]QIUW,CHENCC,XUL,etal.Sub-TgCross-LinkingofaPolyimideMembraneforEnhancedCO2PlasticizationResistanceforNaturalGasSeparation[J].Macromolecules,2011,44(15):6046-6056.]，這種聚合物可以在330℃時(shí)完全交聯(lián)，交聯(lián)機(jī)理如圖1-7(a)所示。交聯(lián)后形成的聚合物膜的選擇性幾乎不變，滲透性和抗塑化性都得到了很大的提升。另外退火時(shí)間和溫度都可以通過(guò)影響聚合物膜的交聯(lián)程度而間接影響選擇性。Tian等制備了玻璃化轉(zhuǎn)變溫度為450℃的側(cè)鏈含羧基的三蝶烯基聚酰亞胺[[]QIUW,CHENCC,XUL,etal.Sub-TgCross-LinkingofaPolyimideMembraneforEnhancedCO2PlasticizationResistanceforNaturalGasSeparation[J].Macromolecules,2011,44(15):6046-6056.[]TIANZK,CAOB,LIP.Effectsofsub-Tgcross-linkingoftriptycene-basedpolyimidesongaspermeation,plasticizationresistanceandphysicalagingproperties[J].JournalofMembraneScience,2018,560:87-96.圖1-7兩種熱誘導(dǎo)交聯(lián)機(jī)理：（a）脫羧交聯(lián)（b）熱氧化交聯(lián)Fig.1-7Twothermally-inducedcross-linkingmechanisms:(a)Decarboxylationcrosslinking(b)ThermaloxidativecrosslinkingZhang等合成了兩種含內(nèi)酯環(huán)側(cè)基的6FDA-MPP與6FDA-PP聚酰亞胺[[]ZHANGC,CAOB,LIP.Thermaloxidativecrosslinkingofphenolphthalein-basedcardopolyimideswithenhancedgaspermeabilityandselectivity[J].J