【作者】 谢锐；

【导师】 褚良银；

【作者基本信息】 四川大学 ， 化工过程机械， 2007， 博士

【摘要】 温度响应膜和分子识别膜在控制释放、物质分离、手性拆分等方面具有广阔的应用前景。迄今,有关同时具有温度响应和分子识别特性的智能开关膜研究的报道非常少,而将此类开关膜用于手性拆分的研究尚未见到报道。因此,深入研究该类型智能膜的制备方法、构效关系以及响应机理,从而进一步构造具有良好性能的特异分子识别分离膜具有十分重要的意义。本文在不同类型的修饰环糊精单体制备、聚(N-异丙基丙烯酰胺)(PNIPAM)和修饰环糊精共聚高分子以及PNIPAM开关膜制备与性能的研究基础上,设计并成功制备了一种温敏型分子识别智能膜,探明了其制备方法与工艺,研究了其微观结构可控性及其与分离性能之间的关系,考察了其温度控制的分子识别能力和手性拆分能力,取得了一些创新性研究成果。PNIPAM是一类具有低临界溶解温度(LCST)的温度响应型聚合物,其均聚物相变温度在30~34℃之间,且具有较快的响应速度,因此成为温敏开关膜研究中最常采用的温敏材料。β-环糊精(CD)是由7个α-D-吡喃葡萄糖单元通过α-1,4糖苷键首尾相连形成的截锥状的大环化合物,它具有疏水的内部空腔和亲水的外表面,空腔尺寸与萘环的尺寸相匹配,因此能与多种无机、有机小分子和手性客体分子形成主-客体或超分子配合物。核孔膜具有窄孔径分布的标准圆柱形直通孔,是用于研究智能膜微观结构形态以及智能膜响应机理的理想多孔基材膜。本研究采用等离子体诱导接枝聚合法,或等离子体诱导接枝聚合法与化学反应法相结合的方法在聚对苯二甲酸乙二酯(PET)核孔膜上接枝PNIPAM和修饰环糊精,从而得到同时具有温度敏感和分子识别性能的智能膜。由于天然CD不具有与NIPAM发生共聚反应或化合反应的基团,因此需对其进行改性。本研究采用不同的合成方法制备了三种具有不同取代基长度的6位单取代含双键的修饰环糊精单体,它们分别是6位单取代脱氧N-烯丙酰基乙二胺代β-环糊精(AACD)、6位单取代脱氧N-烯丙胺代β-环糊精(ACD)和6位单取代脱氧甲基丙烯酸-2-羟丙基己二胺代环糊精(GMA-HAD-CD)。其中,由于ACD合成步骤较少,合成的产率与纯度均较高。另外,AACD的第二步中间体乙二胺代环糊精(EDA-CD)可用作PNIPAM共聚高分子化合反应的修饰环糊精单体。由于很难对接枝膜上高分子链的成分、链长度和LCST等性质进行表征,本研究制备了聚(N-异丙基丙烯酰胺共聚甲基丙烯酸-2-羟丙基乙二胺基环糊精)(P(NIPAM-co-GMA/CD))共聚高分子,并对其温度响应特性和分子识别能力进行考察。当高分子中GMA含量较小时(NIPAM与GMA投料摩尔比为19.5 : 1),P(NIPAM-co-GMA)高分子溶液的温度响应特性与PNIPAM高分子相似,但是LCST有所减小。然而,固定CD的P(NIPAM-co-GMA/CD)高分子的温度响应性比P(NIPAM-co-GMA)高分子有所降低,但仍然具有分子识别能力。在水溶液中P(NIPAM-co-GMA/CD)的LCST较P(NIPAM-co-GMA)水溶液有所升高,而在ANS溶液中的LCST较在水溶液中有所减小,但仍高于P(NIPAM-co-GMA)在水溶液中的LCST。采用等离子体诱导接枝聚合法在聚碳酸酯(PC)核孔膜上接枝了PNIPAM,确定PNIPAM接枝膜制备工艺条件(包括单体浓度、聚合温度、聚合时间等接枝工艺条件和照射功率、照射时间等等离子体处理工艺条件)。得到的PNIPAM接枝膜的膜表面和膜孔内覆盖一层均匀的接枝层。随着填孔率逐渐增大,膜孔中填充的PNIPAM接枝层逐渐增厚。当填孔率小于44.2%时,接枝膜具有温度感应特性,此时25℃的水通量小于40℃的水通量,并且随着填孔率的增大,水通量有减小的趋势;当填孔率大于44.2%以后,无论是25℃还是40℃,水通量都变为零,此时接枝膜不再具有温度感应特性。填孔率为23.9%的接枝膜表现出较好的温度感应特性,它的孔径在LCST附近(28℃~34℃)发生突变(34℃的孔径为28℃的近两倍),而在T<28℃和T>34℃时保持不变。空白膜的表面接触角随温度的升高而略有减小,而接枝膜的接触角随着温度的升高而增大,水通量的开关特性主要取决于孔径的变化而不是膜表面亲疏水性的改变。分别采用等离子体诱导过氧化自由基接枝聚合法和等离子体诱导自由基接枝聚合法成功地制备了聚(N-异丙基丙烯酰胺共聚N-烯丙胺代β-环糊精)(P(NIPAM-co-ACD)-g-PET)接枝膜。向单体溶液中加入十二烷基硫酸钠、二甲亚砜和N,N-二甲基甲酰胺,有利于提高聚合反应温度,从而增大接枝率。采用等离子诱导自由基接枝聚合法与化学反应法相结合的方法成功地制备聚(N-异丙基丙烯酰胺共聚甲基丙烯酸-2-羟丙基乙二胺基β-环糊精)接枝PET膜(P(NIPAM-co-GMA/CD)-g-PET)。采用适当的单体投料比得到的具有适当接枝率的P(NIPAM-co-GMA)-g-PET膜(NIPAM和GMA投料摩尔比为2.9: 1,Y=1.47%),表现出较好的温度响应特性。它在高温时(34~40℃)的孔径是低温时(25~28℃)的1.15倍左右,PNIPAM接枝膜(Y=1.42%的)为1.29倍。当单体NIPAM和GMA的投料摩尔比为1.6: 1时,接枝率为2.67%时P(NIPAM-co-GMA)-g-PET膜才具有温敏性,但由于通量很小,温度开关作用也不明显。随着接枝链中GMA的比例增大,P(NIPAM-co-GMA)接枝膜的温度响应性越差,欲得到较好的温度响应特性,需在一定程度上提高接枝率。得到的具有温敏特性的P(NIPAM-co-GMA)接枝膜的开关温度仍在32℃附近。P(NIPAM-co-GMA/CD)-g-PET接枝膜的表面接触角表现出温度响应特性,当温度从25℃上升到45℃,接触角增大,而此时PET空白膜的表面接触角减小,说明P(NIPAM-co-GMA)-g-PET接枝膜的水通量主要依赖于孔径的变化而不是膜表面亲疏水性的变化。固载CD的PGMA/CD-g-PET和P(NIPAM-co-GMA/CD)-g-PET膜对D,L-色氨酸(D,L-Trp)具有一定手性拆分能力,其手性拆分过程属于阻碍传输机理。室温下的拆分实验中,PGMA/CD接枝膜(Y=3.08%,CD的含量为11.0μg/cm2)的拆分能力比PGMA-g-PET膜(Y=2.53%)大,对映体过量值(e.e.%)先增大后减小(最大e.e.%约为7%),优先透过D-Trp。P(NIPAM-co-GMA/CD)接枝膜的e.e.%也是先增大后减小。CD固载量较小的P(NIPAM-co-GMA/CD)接枝膜的e.e.%也较小,含量为2.6μg/cm2的接枝膜的最大e.e.%接近7%,而CD含量为11.5μg/cm2的接枝膜最大e.e.%为10%。由于CD的促进传输作用,无论25℃还是40℃,ANS在PGMA/CD-g-PET膜(Y=3.07%,CD含量为5.6μg/cm2)中的扩散都比在PGMA-g-PET膜(Y=3.27%)中快。由于高温时CD与ANS的包结配位常数较小,因此CD对ANS的促进传输作用就更强。40℃时ANS通过PGMA/CD接枝膜的扩散系数与25℃的差值,比通过PGMA接枝膜的扩散系数在40℃和25℃差值更大,40℃时ANS在PGMA/CD接枝膜的扩散系数比在空白膜中的略高。ANS吸附实验表明,P(NIPAM-co-GMA/CD)-g-PET膜对ANS的吸附主要是CD的包结作用,PET基材和P(NIPAM-co-GMA)接枝膜对ANS的吸附作用较小。ANS在P(NIPAM-co-GMA/CD)-g-PET膜上表现出“低温吸附-高温解吸”的现象,并且具有良好的重复性,这主要是由于P(NIPAM-co-GMA)链的“伸展-收缩”构象变化和主体分子CD对ANS较强的包结能力共同作用的结果。CD对ANS包结配合时,ANS分子的萘环进入CD空腔,苯环部分留在CD空腔之外。在温度较低时(T<LCST),P(NIPAM-co-GMA)链由于PNIPAM呈伸展构象而舒展,CD-ANS配合物周围有足够的空间,因此ANS更容易进入CD空腔,此时CD-ANS的包结配合稳定系数比较高。当温度升高时(T>LCST),P(NIPAM-co-GMA)链收缩,CD-ANS配合物周围比较拥挤,造成CD-ANS的包结配合稳定系数下降,ANS容易从CD空腔中脱落出来。随着CD含量增加,P(NIPAM-co-GMA/CD)-g-PET膜对ANS单位吸附量在低温和高温的差值越大。荧光光谱分析表明,吸附在P(NIPAM-co-GMA/CD)-g-PET膜上客体分子ANS可以通过高温水洗进行洗脱,实现客体分子的再利用和接枝膜的再生。综上所述,本研究成功地设计并制备了具有温度敏感的分子识别开关膜,通过温敏性通量实验、手性分子拆分实验、客体分子识别的吸附实验,证明所制备的开关膜具有手性分子拆分能力和客体分子识别能力,并且通过改变环境温度可以较好的实现客体分子的再利用以及开关膜的再生。更多还原

【Abstract】 Thermo-responsive gating membranes and molecular recognizable gating membranes have wide potential applications in the fields of controlled release, substance separation, and chiral resolution, etc. Up to now, few literatures have been reported on intelligent gating membranes possessing both thermo-responsive and molecular recognizable characteristics simultaneously. Moreover, investigations on chiral resolution employing such membranes are still lacking. Therefore, it has substantial significances to systematically investigate the preparation technology, the relationship between structure and performance, and stimuli-responsive mechanism of such thermo-responsive and molecular recognizable gating membranes, which are the key fundaments for designing and fabricating membranes with good performance for the separation of special molecules. In this study, a new type of thermo-responsive and molecular recognizable intelligent membranes was designed and successfully prepared based on the successful preparation of different modified cyclodextrin, copolymer of poly(N-isopropylacrylamide) (PNIPAM) and modified cyclodextrin, and PNIPAM grafted gating membranes. The preparation technology, the controllable property of microstructure, and the relationship between microstructure and separation performance of such membranes were investigated systematically. The molecular recognizable capability controlled by temperature and the chiral resolution capability of such membranes were also experimentally studied.PNIPAM is a thermo-responsive polymer which has lower critical solution temperature (LCST) around 30~34 oC and its responsiveness is fast. Therefore, PNIPAM is a widely-used thermo-sensitive material in the study of thermo- responsive gating membranes.β-Cyclodextrins (CDs) with seven glucose residues, are torus-shaped molecules composed of cyclicα-1,4-oligoglucopyranosides. Because of their structure of hydrophobic cavities with size suitable for naphthalene ring and of hydrophilic external surfaces, CDs can recognize many inorganic, organic and chiral compounds and selectively include them in their cavities to form host-guest or supramolecular complexes. Track-etched (TE) membrane with straight cylindrical pores perpendicular to the surface and narrow pore size distribution is a favorable porous substrate membrane used to study microstructure morphology and stimuli-responsive mechanism of smart membranes. In this study, smart membranes with both thermo-responsive and molecular recognizable characteristics were prepared by grafting both NIPAM and modified CD monomers onto polyethylene terephthalate (PET) TE membrane by employing plasma-induced grafting polymerization or the combined method of plasma-induced grafting polymerization and chemical reaction.Natural CDs do not have active groups to react with NIPAM, so they need to be modified before polymerization. Three modified CDs, mono-6-deoxy-6-(N-acryl- oxyethylenediamino)-β-cyclodextrin (AACD), mono-6-deoxy-6-(N-allylamino)-β- cyclodextrin (ACD) and mono-6-deoxy-6-(2-hydroxypropyl methacrylate-hexane- diamino)-β-cyclodextrin (GMA-HAD-CD), which have double bond and different length of substituted group, were synthesized. Compared with AACD and GMA- HAD-CD, ACD has less synthesis step and therefore its yield and purity were higher.The intermediate product ethylenediamino-β-cyclodextrin (EDA-CD) in the second step of preparing AACD could also be used as monomer to react with PNIPAM. Because it is difficult to analyze the properties such as composition, chain length and the LCST of polymer grafted on the substrate membrane, poly(N-isopropylacrylamide-co-2-hydroxypropyl methacrylate ethylenediamino-β- cyclodextrin) P(NIPAM-co-GMA/CD) polymer was synthesized, and thermo- responsive characteristics and molecular recognizable capability of such a polymer were experimentally studied. When GMA content in the copolymer was small (feeding molar ratio of NIPAM and GMA was 19.5: 1), P(NIPAM-co-GMA) copolymer had thermo-responsive characteristics similar to homopolymer PNIPAM, but its LCST became smaller than that of PNIPAM. The thermo-responsive characteristics of CD-immobilized copolymer P(NIPAM-co-GMA/CD) became a little worse, however, their molecular recognizable capability was still remained. The LCST of P(NIPAM-co-GMA/CD) copolymer was higher than that of P(NIPAM-co-GMA) copolymer in aqueous solution. When P(NIPAM-co-GMA/CD) copolymer was dissolved in ANS aqueous solution, its LCST became lower than that in aqueous solution but still higher than that of P(NIPAM-co-GMA) copolymer in aqueous solution.PNIPAM was successfully grafted on the surface and in the pores of the polycarbonate (PC) TE porous membrane by plasma-induced grafting polymerization, and the preparation technical conditions, including grafting technical conditions such as monomer concentration, polymerization temperature and time, and plasma treating technical conditions such as treating power and time, were experimentally investigated. The grafted PNIPAM polymers were formed onto the membrane surface and inside the pores throughout the entire membrane thickness, and the PNIPAM polymers were filled in the membrane pores gradually with the increase of the pore-filling ratio (F). For the PNIPAM-g-PCTE membranes with F is smaller than 44.2%, the water flux at 40 oC was always larger than that at 25 oC. With the F increasing, the water flux of PNIPAM-grafted membranes decreased at 25 oC as well as at 40 oC. However, when F was too large (> 44.2%), the water flux of PNIPAM grafted membranes became zero no matter what the environmental temperature was. The pore diameter of the PNIPAM-g-PCTE membrane with F = 23.9% increased dramatically when the temperature changed from 28 to 34 oC, but kept unvaried at the temperatures lower than 28 oC and/or higher than 34 oC (pore size at 34 oC was nearly two times as that at 28 oC). The contact angle of PNIPAM-g-PCTE membrane increased largely when the temperature increased, while that of substrate membrane became a little smaller at the same environmental temperature. The thermo-responsive gating characteristics of the water flux of PNIPAM-g-PCTE membranes were mainly dependent on the pore size change rather than the variation of membrane surface hydrophilicity.Poly(N-isopropylacrylamide-co-N-allylamino-β-cyclodextrin)-g-PET (P(NIPAM-co-ACD)-g-PET) membranes were successfully prepared by employing plasma-induced peroxide radical grafting polymerization method and plasma-induced free radical grafting polymerization method, respectively. The addition of sodium dodecyl sulfate, dimethylsulfoxide and N,N-dimethylformamide into monomer solution, was helpful to improve the reaction temperature and consequently obtain higher grafting yields (Y). Poly(N-isopropylacrylamide-co- 2-hydroxypropyl methacrylate ethylenediamino-β-cyclodextrin)-g-PET (P(NIPAM-co-GMA/CD)-g-PET) membranes were successfully prepared by the combined method of plasma-induced free radical grafting polymerization and chemical reaction. P(NIPAM-co-GMA/CD)-g-PET membranes with appropriate grafting yield (Y=1.47%) prepared by appropriate feeding molar ratio of monomers (e.g. feeding molar ratio of NIPAM and GMA was 2.9 : 1) showed good thermo-responsive characteristics, whose pore diameter at higher temperature (34~40 oC) was about 1.15 times as that at lower temperature (25~28 oC) compared with 1.29 times of PNIPAM-g-PET membrane (Y=1.42%). When feeding molar ratio of NIPAM and GMA was 1.6 : 1, P(NIPAM-co-GMA)-g-PET membrane with Y=2.67% showed thermo-responsive characteristics. However, because the water flux was small, the thermo-responsive gating effect was not significant. With the ratio of GMA in grafted polymer increasing, the thermo-responsive characteristics of P(NIPAM-co-GMA)-g-PET membranes became worse. To obtain better thermo- responsive characteristics, it is necessary to increase grafting yield to some extent. The gating temperatures of resultant thermo-responsive P(NIPAM-co-GMA)-g-PET membranes were still around 32 oC. The contact angle of P(NIPAM-co-GMA/CD)- g-PET membrane also showed thermo-responsive characteristics. When the temperature increased, the contact angle of P(NIPAM-co-GMA/CD)-g-PET membrane increased largely, whereas that of substrate membrane became smaller at the same time. The thermo-responsive characteristics of the water flux of P(NIPAM-co-GMA)-g-PET membranes were mainly dependent on the pore size change rather than the variation of membrane surface hydrophilicity.CD-immobilized PGMA/CD-g-PET and P(NIPAM-co-GMA/CD)-g-PET membranes could discriminate D,L-tryptophan (D,L-Trp), and the chiral resolution process was based on redarded transport methanism. PGMA/CD-g-PET membrane (Y=3.08%,CD content is 11.0μg/cm2) has better chiral resolution capability toward D-Trp than PGMA-g-PET (Y=2.53%) at 25 oC. The enantiomeric excess (e.e.%) firstly increased and then decreased as time increased, and the maximal e.e.% of PGMA/CD-g-PET membrane was 7 %. The e.e.% of P(NIPAM-co-GMA/CD)-g- PET membrane was also increased first and then decreased. The less the CD content was, the smaller the e.e.% of P(NIPAM-co-GMA/CD)-g-PET membrane. When CD content was 2.6μg/cm2, the maximal e.e.% was nearly 7%; while the maximal e.e.% was 10% for 11.5μg/cm2. ANS diffused faster through PGMA/CD-g-PET membrane (Y=3.07%, CD content was 5.6μg/cm2) than through PGMA-g-PET membrane (Y=3.27%) at both 25 oC and 40 oC, because of the facilitated transport function of CD. Because of the association constant of ANS with CD was smaller at higher temperature, the facilitated transport of CD toward ANS was enhanced at higher temperature. The difference between diffusion coefficient of ANS through PGMA/CD grafted membrane at 40 oC and that at 25 oC was larger than that through PGMA grafted membrane. The diffusion coefficient of ANS through PGMA/CD-g- PET membrane at 40 oC was even larger than that through substrate membrane. The adsorption of ANS onto P(NIPAM-co-GMA/CD)-g-PET membrane was mainly due to stronger recognition capability of CD toward ANS, while the adsorption of the substrate and P(NIPAM-co-GMA)-g-PET membrane toward ANS was weaker. ANS adsorbed onto P(NIPAM-co-GMA/CD)-g-PET membrane at lower temperature (i.e. 25 oC) and desorbed from P(NIPAM-co-GMA/CD)-g-PET membrane at higher temperature (i.e. 40 oC) with good repeatability. The reason mainly existed in both the“swollen-shrunken”configuration change of P(NIPAM-co-GMA) grafted chains around LCST and the stronger recognition of CD toward ANS. ANS was partially captured in the CD cavity with naphthalene group enclosed in the cavity and benzene ring residing outside the cavity. At lower temperature (T < LCST), the P(NIPAM-co-GMA) copolymer swells, and steric hindrance from the polymer near the cavities is small, guest molecules can easily enclose into the cavity, so that the associated constant is higher. However, at higher temperature (T > LCST), the P(NIPAM-co-GMA) copolymer shrinks, and the polymer chains agglomerate around the cavity, increasing the steric hindrance, which leads to a smaller binding constant. As CD content increased, the difference between adsorption amount of ANS onto P(NIPAM-co-GMA/CD)-g-PET membrane at 25 oC and that at 40 oC became larger. ANS adsorbed on the P(NIPAM-co-GMA/CD)-g-PET membrane could be washed away by water at higher temperature, and the membrane could be regenerated.In summary, a novel thermo-responsive and molecular recognizable gating membrane was designed and successfully prepared. The guest-molecule recognition and chiral-molecule discrimination capability were experimentally studied by thermo-responsive flux experiment, chiral resolution experiment and guest-molecule adsorption experiment. The results showed that guest molecules can be separated and the membrane can be regenerated simply by changing the environmental temperature.更多还原