【作者】 孙波；

【导师】 米镇涛； 欧阳杰；

【作者基本信息】 天津大学 ， 化学工艺， 2006， 博士

【摘要】 环境友好型化学品—聚天（门）冬氨酸（PAA）是一种具有多肽结构的可降解生物高分子物质。研究开发各种类型的PAA材料,并进行应用研究已成为世界各国共同感兴趣的课题,力图将这些材料直接应用于某些重要领域,或替换目前在一些重要领域中正在使用的有害物质。本工作重点研究开发具有脱除重金属功能的聚天冬氨酸材料,研究其结构与性能之间的“构效关系”,并尝试将它们应用于脱除中药中重金属这一领域,具有重要的理论意义和实用价值。本文的主要工作和得出的重要结论如下:1.首先采用分散悬浮聚合方式,研究了（线性）聚天冬氨酸（盐）的前驱体—聚丁二酰亚胺的合成。详细考察了聚合过程中原料粒度、反应温度、反应时间、催化剂及其用量等因素对分子量及分布的影响。实验结果表明,对分子量及分布影响最大的因素是原料粒度和聚合温度,在减小原料L-或DL-天冬氨酸的粒度并提高聚合温度（²40℃）的条件下,可得到重均分子量20 000³0 000的聚丁二酰亚胺（以聚苯乙烯为标准）,分子量分布系数为1.3¹.5。H3PO4为适宜催化剂,加入适量的H3PO4,既可保护-NH2,减少副反应;又可降低聚合反应的活化能,加快聚合反应,缩短反应时间;还可提高分子量。但催化剂过量时起封端作用,不利于分子量的提高,因此可用催化剂用量调节分子量。2.以对水溶液中Ca2+的阻垢效果为目标函数,运用正交试验设计研究了聚丁二酰亚胺碱性水解制备（线性）聚天冬氨酸（盐）的反应过程。考察了水解温度、水解时间、碱的浓度和用量等因素对（线性）聚天冬氨酸（盐）分子量的影响。实验结果表明,对分子量影响最大的因素是水解温度;由实验结果可推测聚丁二酰亚胺的碱性水解动力学为2级连串反应;在此基础上估算出聚丁二酰亚胺中酰亚胺环（结构单元）水解反应的活化能为28.1 kJ/mol,而聚天冬氨酸中酰胺水解反应的活化能为40.1 kJ/mol。3.阻垢性能测试表明,若以制备阻垢剂为目的,无论采用何种原料路线（L-或DL-天冬氨酸还是顺丁烯二酸酐）,只要反应条件适宜均可得到具有优异阻垢性能的聚天冬氨酸。不同原料得到的聚天冬氨酸的阻垢效果相差不大,与目前正在使用的聚丙烯酸型水处理剂的阻垢性能相仿。当采用分散悬浮聚合法时,制备具有优异阻垢性能的聚天门冬氨酸的适宜聚合条件为220℃,0.02⁰.03 mol H3PO4/mol L-天门冬氨酸,反应时间为1.5 h,产品阻垢率90⁹5%,产品色浅;适宜水解条件为:水解温度50⁹0℃,水解时间约30 min,NaOH浓度2 mol/L,用量为与聚丁二酰亚胺等摩尔数（每克聚丁二酰亚胺约0.45⁰.48 g NaOH）。聚天门冬氨酸（钠）以络合增溶、晶格畸变、凝聚分散等三种方式发挥阻垢作用。4.运用离子选择电位法研究了聚天冬氨酸材料的一次化学结构——线性聚天冬氨酸（钠）对重金属Pb2+的吸附作用,实验结果表明,线性聚天冬氨酸（钠）对Pb2+有很强的吸附作用,它不仅吸附容量高（按聚丁二酰亚胺质量计为1.0 g Pb2+/g ）,而且具有较低的平衡吸附浓度（<0.25 mg Pb2+/L）;尽管线性聚天冬氨酸及其Pb2+盐是水溶性的,但它对Pb2+的平衡吸附数据仍可用Langmuir和Freundlich方程较好的拟合。5.以重均分子量为10 000～30 000的聚丁二酰亚胺（以聚苯乙烯为标准）为原料,选用适宜的交联剂,采用微波技术合成了非水溶性聚天冬氨酸水凝胶。探讨了原料配比、反应温度或加热方式、反应时间、交联剂及其用量等对反应的影响。实验结果显示:聚天冬氨酸水凝胶也是优良的Pb2+吸附剂,它对Pb2+的吸附量随溶液中Pb2+的浓度、pH等的变化而不同,但受温度的影响较小,而且达到吸附平衡所需要的时间短。初步研究表明,适宜的脱附剂是柠檬酸/柠檬酸三钠和乙酸/乙酸钠混合物。根据红外光谱数据推测聚天冬氨酸水凝胶对Pb2+的吸附作用既有离子交换作用又有配位络合作用。6.在研究聚天冬氨酸水凝胶的制备工艺中,探索了以水为介质的清洁制备工艺,通过加入钙模板剂,提高了聚天冬氨酸水凝胶的强度和吸附容量。实验结果表明,加入Ca²⁺模板剂后,聚天冬氨酸水凝胶对Pb²⁺的吸附性能有所增强,而且也增强了水凝胶的强度。聚天冬氨酸水凝胶的吸附容量约为4.0 mmol/g。7.将带有胺基侧链的聚天冬氨酸与壳聚糖交联共聚,开发了一种新型“绿色”高分子材料—聚天冬氨酸与壳聚糖共聚物,其结构与与细胞壁的肽聚糖结构相似。它遇水体积膨胀系数小,可用于固定床操作。采用不同的制备工艺,可制得不同形式的聚天冬氨酸与壳聚糖共聚物材料,例如颗粒型,膜型,巯基型。研究了合成过程中各种因素的影响。通过实验确定了制备颗粒型聚天冬氨酸与壳聚糖共聚物的适宜条件为:壳聚糖:带胺基侧链的聚天冬氨酸（g/g）=1:1.5,0.5～1.0 ml 50 %戊二醛/g （带胺基侧链的聚天冬氨酸）,所得共聚物的含N量约8.0 %。在制备聚天冬氨酸与壳聚糖共聚物的过程中,加入适宜的致孔剂,可制得既具有离子交换/吸附功能,又具有一定孔径的双功能超滤膜。此外,将制得的聚天冬氨酸与壳聚糖共聚物与巯基乙酸反应,还可制得含巯基的聚天冬氨酸与壳聚糖的共聚物,巯基含量约为2.0 %。巯基的存在可能会有利于脱除有机重金属离子（例如甲基汞等）。聚天冬氨酸与壳聚糖的共聚物对原料聚丁二酰亚胺的分子量要求不高,可利用较低分子量的聚丁二酰亚胺作为原料。8.系统研究了聚天冬氨酸材料脱除重金属离子的功能,通过改变结构中的官能团,研究了“构效”关系。通过比较几种具有不同侧链聚天冬酰胺衍生物对Pb²⁺的作用,证实聚天冬氨酸盐是聚天冬酰胺衍生物中最理想的重金属去除剂。它单位质量捕集容量大,极限平衡浓度低。既可用于重金属浓度较高的场合,又可用于重金属浓度较低的场合。实验结果还显示,交联聚天冬氨酸水凝胶的除铅性能优于聚丙烯酸基树脂和一般螯合树脂,也优于天然高分子材料壳聚糖。红外光谱数据和XPS分析显示聚天冬氨酸水凝胶对Pb²⁺的作用同时存在离子交换作用和配位络合作用。结合线性聚天冬氨酸对Pb²⁺的吸附数据,可推测Pb²⁺与聚天冬氨酸形成配位数为4的络合物。与此同时,以Ca²⁺为参照物,通过实验证实聚天冬氨酸对重金属离子Cd²⁺和Hg²⁺的吸附作用机理与对Pb²⁺吸附作用机理相似。9.将聚天冬氨酸材料应用于脱除中药中的重金属。选择了几种重金属含量较高的中草药来考察聚天冬氨酸材料脱除中药中重金属的能力。实验结果显示,聚天冬氨酸水凝胶可有效除去甘草、当归、绞股兰等中药水溶液中的Pb²⁺、Hg²⁺、Cd²⁺等二价重金属离子,中药浓度（或固含量）对水凝胶吸附性能有一定的影响;但实验也发现,聚天冬氨酸结构对以其它形式存在的Hg元素的脱除效果不好。而含巯基聚天冬氨酸与壳聚糖共聚物既可有效脱除中药中的Pb和Cd元素,也可有效脱除Hg元素。10.通过BOD/COD、总有机碳法（TOC）变化、生长分级、质量变化、扫描电镜,元素分析、红外光谱等多种分析测试手段,评价了各种类型的聚天冬氨酸材料的生物降解性。实验结果表明,在评价水溶性聚天冬氨酸生物降解性的方法中,总有机碳法（TOC）法比较好。该方法实验操作较简单,数据可靠,重复性好;按照OECD 201B标准,经过驯化接种后,水溶性聚天冬氨酸属于易生物降解聚合物。评价非水溶性聚天冬氨酸材料生物降解性的适宜方法是生长分级法并配合扫描电镜,失重法并配合残余物元素分析、红外光谱分析等;实验结果显示,聚天冬氨酸与壳聚糖共聚物的生物降解性优于聚天冬氨酸水凝胶,二者生物降解性均比市售凝胶型聚丙烯酸类离子交换树脂110好。更多还原

【Abstract】 Polyaspartate （PAA） is typical of environmentally friendly chemicals and the macromolecule with a biodegradable polypeptide structure. Developing various kinds of polyaspartate （PAA） and extending their application have attracted a great deal of worldwide attention, in order to put directly them to a good use or substitute harmful substances in some key fields. It is of great theoretical and practical significance to focus on synthesis of polyaspartate （PAA） materials with an excellent heavy-metal-removing performance, investigation of relation of structure-activity, and their application to some Chinese herbal medicines. The main contents, conclusions and results are as follows:1. Polysuccinimide, precursor of polyaspartate, was synthesized by suspension polycondensation of L-aspartic acid dispersed in a medium. The effects of catalyst,temperature,time and particle size of L-aspartic acid on molecular weight （ M w） and its distribution were investigated deliberately.The experimental results revealed that particle size of L-aspartic acid and temperature are the major factors affecting the molecular weight of the product. Polysuccinimide, having a weight average molecular weight of 20 000³0 000 and M w/ M ndistribution of 1.3¹.5, was obtained under appropriate conditions. The results also showed that H3PO4 as the catalyst can prevent–NH2 group from side reactions,accelerate the rate of polymerization and increase M w, but an excess of catalyst results in closing end-group, and so blocks the increase in M w.2. Taking inhibition of calcium in aqueous solution as a probe, conversion of polysuccinimide to polyaspartate by alkaline hydrolysis was investigated by means of orthogonal experimental design. The effects of temperature, time, concentration and amount of NaOH on the scale inhibition capacity and molecular weight （ M w） of the hydrolysis products were taken into account. The experimental results indicated that the reaction temperature is the key factor affecting the molecular weight of the polymer, and the kinetics of the hydrolysis reaction was deduced to be a 2nd order cascade type reaction. Approximate calculation values of the activation energy of the hydrolysis reaction of succinimide unit in polysuccinimide and amide unit in polyaspartate were 28 mol/kJ and 40 mol/kJ, respectively.3. Scale inhibition performance test demonstrated that for the purpose of preparinginhibitor of calcium,no matter what starting substance was, such as L-aspartic acid, DL-aspartic acid, or maleic anhydride, polyaspartate with excellent scale inhibition the scale inhibition can be available under appropriate conditions. Polyaspartates from different raw materials are similar in inhibition performance, and competitive with polyacrylic acid-based water treatment chemicals. The appropriate polycondensation conditions of L-aspartic acid by means of suspension polymerization were 0.02⁰.03 molH3PO4/mol L-aspartic acid , 220℃and 1.5 h, with a 90⁹5 % scale inhibition and light colour. The appropriate conditions of the hydrolysis of polysuccinimide determined by means of an orthogonal experimental design were 2 mol/L NaOH （in water）, 0.45⁰.48 g NaOH / g polysuccinimide, 50⁹0℃and 30 min. Polyaspartate plays the scale inhibition role of increasing dissolvability by complexing, distorting crystal lattice and dispersing aggregate.4. Pb²⁺-binding behavior of linear polyaspartate, the primary structure of polyaspartate material, was evaluated by potentiometer determination. It was demonstrated that the linear polymer exhibits higher Pb²⁺ uptake capacity (about 1.0 g Pb²⁺ /g,based on amount of polysuccinimide) and lower Pb²⁺ equilibrium concentration (<0.25 mg Pb²⁺/L). It was noticeable that the uptake is still high even in the range of lower concentration of Pb²⁺. The equilibrium sorption data for Pb²⁺ on polyaspartate fitted well with Freundlich and Langmuir models in spite of its dissolving in water.5. Crosslinked polyaspartate hydrogels were prepared by crosslinking polysuccinimide, having a weight average molecular weight of 10 000³0 000, with diamine used as cross-linking agents. Microwave technique was adopted in the process. Effects of reactant molar ratio, temperature or heating mode and reaction time on crosslinking were discussed. The experimental results showed that reaction time was shortened remarkably and temperature had little effect on the reaction by use of microwave technique. Polyaspartate hydrogel also exhibits to be an effective agent for removal of Pb²⁺, and its Pb²⁺ uptake varied with concentration of Pb²⁺ in solution, pH of media, and so on. Temperature had little effect on its binding performance, and only a short period for reaching equilibrium was required. Citrate and acetates were preferably desorbing agents. By means of infrared spectra （IR）, it is inferred that polyaspartate hydrogel bound Pb²⁺ by both ion exchange mechanism and chelating mechanism6. A clean process using water as the solvent media was explored for the preparation of Polyaspartate hydrogel, and meanwhile Ca2+ template was adopted to improve thestrength and uptake capacity of gel. The experimental results showed that the gel having better strength and uptake capacity was obtained, with an uptake capacity of about 4.0 mmol per gram of dry gel.7. A novel and green polymer with similar structure with peptidepolysaccharide, the copolymer of ployaspartate and chitosan, was developed by the copolymerization of chitosan and ployaspartate with the side amino-group. The copolymer can be used for the packed bed due to its lower expansion performance in the presence of water. Several types of the copolymer, such as granule, membrane and thiol-type, can be prepared with different methods. The appropriate conditions for the granule type copolymer were experimentally obtained: chitosan: ployaspartate with the side amino-group （g/g）=1:15, 0.5¹.0 ml 50% glutaraldehyde / g （ployaspartate with the side amino group）, The addition of appropriate pore-forming agents in the copolymerization of chitosan and ployaspartate gave a bifunctional ultrafiltration membrane of ion exchange and adsorption with porosity. When the copolymer reacts with thioglycollic acid, a new copolymer containing 2% （wt.） thiol content can be obtained. The presence of thiol group may be helpful to the removal of organic heavy metal ions, such as CH3Hg+ etc.8. The researches on the function of polyaspartate material for heavy-metal removal and on the relation between structure and its activity were conducted systematically. It was verified that polyaspartate is a more excellent Pb²⁺-binding agent by comparison with some polyaspartamide derivatives having different side chains in that it possesses higher Pb²⁺ uptake and lower Pb²⁺ equilibrium concentration. It was suitable for application to both higher and lower concentration of heavy metal ions. The experimental results also demonstrated that crosslinked polyaspartate hydrogel is superior to polyacrylic acid-based resins, poly styrene-based chelating resins and chitosan. The infrared spectra （IR） and X-ray photoelectron spectra （XPS） revealed that polyaspartate hydrogel binds Pb²⁺ by both ion exchange mechanism and chelating mechanism. Along with the equilibrium sorption data for Pb²⁺ on polyaspartate and those from IR, it was deduced that the complex is formed between Pb²⁺ and polyaspartate hydrogel and the coordination number of Pb²⁺ is 4. Meanwhile, using Ca²⁺ as a reference, the experimental results showed that Cd²⁺ and Hg²⁺ were bound to polyaspartate hydrogel by the same mechanism as Pb²⁺.9. Polyaspartate materials were introduced into some Chinese herbal medicines to remove heavy metal in them. The performance was tested for their heavy metal-binding behavior in some chosen herbal solutions with a higher heavy metal contents.Polyaspartate materials were demonstrated to be the effective agents for the removal of Pb²⁺, Cd²⁺ and Hg²⁺ from the aqueous solution of glycyrrhizin, angelica or gynostemma pentaphyllum. The concentration of the solutions, or solid content in herbal medicine solution, had an influence on their performance. Except for Hg²⁺, Polyaspartate structure was found to be ineffective for the removal of mercury in other form. Polyaspartate and chitosan copolymer with thiol group exhibited an excellent elimination of lead, cadmium and mercury.10. The biodegradation of various ployaspartates was systematically investigated using several testing methods, such as BOD/COD, TOC, growth grade rating, loss of weight, scanning electron microscope （SEM）, elemental analysis and infrared spectrum analysis （FT-IR）. The results indicated that TOC is an appropriate method to evaluate biodegradation of water-soluble ployaspartate due to the simplicity of operation, reliability and excellent repeatability of data. According to standard OECD 201B, water-soluble ployaspartate belongs to the ready-biodegradable polymer. Several methods were also suggested to evaluate the biodegradation of water-insoluble ployaspartate. They are growth grade rating with the aid of SEM, loss of weight with the help of elemental analysis and FT-IR of residue. It was found that the biodegradability of copolymer of chitosan and ployaspartate is better than that of polyaspartate hydrogel, and that both the copolymer and polyaspartate hydrogel have a better biodegradability than the commercial polyacrylic acid-based ion-exchange resin 110 （gel type）.更多还原