【作者】 杨惠；

【导师】 杨世伟；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2010， 博士

【摘要】 凭借其超支化的结构、明确的分子量和分子尺寸、可精确控制的分子形状与分枝长度/密度比、独特的单分散性、分子内部存在的空腔、分子表面的功能性等显著特征,聚酰胺-胺(PAMAM)成为发展最为迅速、研究最为广泛和深入的一类新型树状分子。在此基础上,PAMAM基树状分子以其独特的分子结构和物理化学性质在众多领域有着广泛的应用前景,并迅速发展为研究热点之一。此类分子具有良好的反应活性以及包容能力,在分子中心或末端引入大量的反应性、功能性基团,因此可以作为纳米粒子和药物分子的模板或者蛋白质、酶、病毒等理想的合成模拟物,也可以在内部空腔引入催化剂的活性中心或者在经过修饰的末端基团连接基因、抗体等活性物质,从而成为具有特殊功能的高分子材料。由刚性疏水基团、发色单元修饰的PAMAM树状分子以及将PAMAM与金属离子进行螯合构筑等研究工作大量涌现,尤其是以PAMAM为基础接枝两亲嵌段的树状分子在生物医学、自组装模板、催化剂等诸多方面有着潜在的、巨大的应用前景。然而,对于此类PAMAM基两亲树状分子体系的表面活性、分子聚集行为及其通过pH和盐的可调节性、与小分子表面活性剂的分子间相互作用等的研究却鲜见报导。本文以PAMAM接枝POmEOn(其中PO为环氧丙烷;EO为环氧乙烷;m和n分别代表嵌段中PO和EO的个数)系列两亲树状分子的结构对其物理化学性质以及油水分离性能的影响为中心,通过表面张力、稳态荧光、浊度分析、等温滴定微量量热、动态激光光散射(DLS)、透射电子显微镜(TEM)、原子力显微镜(AFM)等实验手段与方法,研究树状分子的结构对其表面与界面性质、聚集行为的影响,以及pH、盐对聚集体构筑的诱导效应。本文考察树状分子的起始剂(即PAMAM)代数以及嵌段中EO/PO质量比对浊度性质的影响。探讨了在起始剂代数不同的情况下,系列树状分子的浊度性质与浊点(CP)温度等性质的变化规律。随着嵌段EO/PO比例的增大,体系的CP值先升高后逐渐降低,表明EO/PO对于树状分子的亲水、疏水性以及溶解能力具有一定的调节作用。熵增是系列树状分子自发聚集过程中的主要驱动力。当POmEOn嵌段增长时,EOn单元对于氢键的键合起到很大作用,此时体系的聚集在更高浓度下发生,即临界聚集浓度(CAC)升高,同时聚集过程中所产生的吉布斯自由能(ΔGo)增大。研究表明,在此过程中两亲嵌段长度对聚集体尺寸具有一定的调控作用。pH范围对树状分子体系的聚集行为作用显著。当pH值在2至pKa的范围内变化时,溶液澄清,主要由于PAMAM的胺基基团质子化作用完全;当pH值在pKa ~ 7.5的区间变化时,溶液呈现浑浊状态,此时质子化不完全,体系中形成了较大尺寸的聚集体;随着碱性继续增强,质子化进程几乎无法发生,体系产生分相。在pH值从2增加到10的过程中,由于在中性和碱性环境下质子化作用不完全其微环境极性随之增强、CAC逐渐减小。研究盐对树状分子体系聚集行为的影响。其影响顺序为C6H5COONa > Na2SO4 > NaCl,导致CP温度顺序递增。无机盐的影响主要归因于水合作用,即水分子从树状分子的核壳结构迁移至SO42-和Cl-水合层的运动。C6H5COONa的作用主要依赖于苯环插入到聚集体疏水核内部的作用,对聚集体尺寸的增大起到更为显著的效果。研究发现树状分子与表面活性剂的分子间相互作用较强。十二烷基硫酸钠(SDS)在远低于临界胶束浓度(CMC)时,与树状分子的混合体系即表现出较高的浊度性质,由于此时SDS分子插入到胺基基团和疏水微区中从而形成较大尺寸的聚集体。与双十二烷基二甲基溴化铵(DDAB)的多层囊泡体系相比,树状分子与DDAB混合体系的聚集体尺寸与形貌、流变学性质均有较大改变。探讨系列树状分子对油水界面膜的影响,并对脱水清水性能进行评价。研究了随着树状分子浓度的改变其降低油水界面张力的能力以及在界面处的扩张粘度、液滴半生命期、液滴破裂速率常数的变化规律。结果显示,随着起始剂代数的增加树状分子的脱水性能逐渐提高,当EO/PO在嵌段中的质量比例为1:3时脱水效果最佳。更多还原

【Abstract】 Polyamidoamine （PAMAM）, one of the families of novel dendrimers, has been developed the fastest and researched the most intensively for the remarkable characteristics, such as hyperbranched structure, exact molecular weight and size, well-controlled molecular shape and branch length/density ratio, unique monodispersity, cavity inside of molecule, functionality of molecule surface. On that basis, a variety of study fields focus on PAMAM-based dendrimers with particular molecular structure and physical chemistry properties. This kind of molecules has excellent activity and ability of capacity, introducing many reactive and functional groups in the centre or extremity, and therefore, it can be served as a template of nano particle and drug molecule, or the synthesized simulacrum of protein, enzyme and virus. It also can be led the active centre of catalyst into the cavity, or have the terminal groups modified with gene or antibody. Hence dendrimers become macromolecular materials with special functions.Various examples of PAMAM-based dendrimers functionalized with rigid hydrophobic periphery or chromophoric units, or binding metal ions have been emerged in large numbers. Especially, the amphiphilic PAMAMA-based dendrimers have been attracted on potential and enormous application fields, including biology and medicine, assembly template, catalyst, etc. Little attention, however, has been paid to surface active characteristics, aggregation behavior, pH and salt effects on the aggregagtion properties of PAMAM molecules branched with amphiphilic segments, as well as the molecular interactions with micromolecular surfactants. With this in mind, we synthesized a series of dendrimers with PAMAM as the core and PO_mEO_n units （PO and EO are the abbreviations of propylene oxide and ethylene oxide, respectively; m and n are the numbers of PO and EO in a branch, separately） as the branches, and investigated the influence of dendritic structure on the physicochemical properties and the ability in separating oil/water mixture, as well as the effects of pH and salts on the aggregates conformation, through the measurements of surface tension, steady fluorescence, turbidity analysis, isothermal titration microcalorimetry, dynamic light scattering （DLS）, transmission electron microscopy （TEM） and atomic force microscopy （AFM）.The influences of initiator （namely PAMAM） generation and EO/PO ratio of the branch on the turbidity properties were investigated in this paper, respectively. Dendrimers with different generations of PAMAM have different turbidity properties and cloud point （CP） temperatures. As the mass ratio of EO/PO increases, CP first increases, and then decreases gradually, which indicates the ratio of EO/PO could condition the hydrophilic and hydrophobic properties, and the capability of solubility.The gain of entropy is the main driving force for the spontaneous aggregation of the dendrimer series. In the case of longer PO_mEO_n chains, more EO oxygen atoms contribute to hydrogen bonding, and consequently lead aggregates to form at higher concentration, resulting in higher critical aggregation concentration （CAC） and larger Gibbs free energy for aggregation （ΔGo）. In the process, the amphiphilic chain length has impact on the size of aggregates to some extent.pH value has remarkable effect on the aggregation behavior of dendrimers in aqueous solution. When the acidity is below pKa, the dendrimer system is transparent mostly because of the thorough protonation of amide groups of PAMAM; as pH is in the range of pKa 7.5, the protonation process becomes incomplete, which leads dendrimer molecules to form bigger aggregates; with the basic environment coming up, the protonation can hardly take place and the oil phase separates out. With the pH vale increases from 2 to 10, the microenvironment of dendrimer colloid becomes higher polar before aggregates forming and reaches CAC earlier, mainly due to the incomplete protonation process under neutral and basic environment.Salt has an impact on the dendrimer aggregation process in the research. Salt effects on the aggregation behavior in the decreasing order: C₆H₅COONa > Na₂SO₄ > NaCl, resulting in the increase of CP temperature. The influence of inorganic salts is mainly attributed to the hydration process of the preferential movement of water molecules from coordination shells of dendrimer molecules to the hydration layer of SO42- or Cl- ion; and the benzene ring of C₆H₅COONa affects on the size of aggregates significantly, owning to its penetration into the hydrophobic core of aggregates.There is strong interaction between dendrimer and surfactant molecules. When the concentration of added sodium dodecyl sulfate （SDS） is very low such as far from critical micelle concentration （CMC）, the system exhibits higher turbidity which results in bigger aggregates, mainly due to the insert of SDS molecules into amine groups and hydrophobic microdomain. Compared with the multilamellar vesicle system of didodecyldimethylammonium bromide （DDAB）, the mixed system of dendrimer and DDAB exhibits different size and morphology of aggregates, and rheological properties.The demulsification and dehydration properties of dendrimers were discussed, including the ability to decrease interfacial tension and the parameters of dilational viscosity, half life cycle, and rupture speed constant of droplet. The results showed that the dehydration performance of dendrimer can be improved with the generation of initiator increasing, and it comes to the best dehydration result when the ratio of EO/PO in the branch equals to 1:3.更多还原