【作者】 董文勇；

【导师】 颜德岳； 周永丰；

【作者基本信息】 上海交通大学 ， 材料学， 2011， 博士

【摘要】 超支化聚合物是一类具有准球形结构的高度支化大分子,在其不规则的分子结构中含有大量内部空穴和末端官能团。由于超支化聚合物独特的结构和性能特点,目前它已成为高分子领域的研究热点。经过近20年的发展和探索,人们在超支化聚合物的合成、结构表征、功能化改性等方面已经取得了重要进展,尤其是超支化聚合物的合成方法已经趋于全面和成熟,这为超支化聚合物的应用开发奠定了坚实的基础。本文利用活性自由基聚合或者酯化反应对超支化聚合物进行修饰改性从而赋予超支化聚合物新的性质,然后将其用于微/纳米结构的构筑,研究的领域涉及超支化聚合物自组装,通过“breath figure”法制备蜂窝状多孔结构,以超支化分子为模板进行生物矿化等。具体研究内容和主要结论如下:1.端羧基超支化聚醚的pH响应自组装端羟基的超支化聚醚(HBPO-OH)本身不溶于水,当其端基通过改性变为羧基后(HBPO-COOH),其在水溶液中的性质也随之发生变化,从不溶变为可溶,且表现出pH响应自组装行为。在高pH值(pH = 12.21)条件下,由于端羧基完全电离,它以单分子胶束的状态存在于溶液中。随着pH值的降低,由于羧基质子化程度的提高,单分子胶束之间氢键作用不断加强,从而聚集形成一系列不同尺寸的多胶束聚集体。多胶束聚集体的尺寸呈现出pH依赖性,pH值越低,胶束尺寸越大。透射电镜(TEM),动态光散射(DLS),衰减全反射红外(ATR-FT-IR),核磁氢谱(1H NMR)以及原子力显微镜(AFM)的测试结果均证明了HBPO-COOH的pH响应自组装行为。2.基于超支化聚合物构筑具有孤立孔洞结构的蜂窝状有序多孔材料通过可逆加成断裂链转移自由基聚合方法,合成了一种具有超支化聚醚核(HBPO)以及一定数量聚苯乙烯臂(PS)的新型超支化多臂共聚物HBPO-star-PS。然后通过“breath figure”方法,使用HBPO-star-PS作为前驱体,在二维平面上构筑蜂窝状有序多孔膜结构。相比于传统的光刻技术,“breath figure”法的实施过程非常简单——将含有前驱体HBPO-star-PS的氯仿溶液涂于基体表面,然后令其在潮湿的空气中自然挥发,待溶剂和凝结的水滴先后挥发干后,就留下了规则的有序多孔结构。和我们先前报道的结果相比,使用HBPO-star-PS作为前驱体,所得到的蜂窝状多孔膜中六边形排列的孔洞之间没有贯穿,而是由孔壁彼此分隔开来。我们进一步通过调节溶液浇铸体积,聚合物分子量,溶液浓度等参数,可以很方便的控制蜂窝状多孔膜中孔洞的尺寸和结构。多孔膜的水滴接触角测试表明,由于多孔结构的形成,增加了膜表面的粗糙度,使膜表面的疏水性得到显著的提高,接触角从平滑表面的88°增加到孔尺寸为3.12μm时的130°。3.仿生合成具有类贝壳层状微结构的碳酸钙空心球通过将超支化聚合物与双亲水嵌段共聚物的概念结合起来,设计了一种双亲水型的端羧基超支化聚缩水甘油醚(HPG-COOH),并用其作为调控剂,来控制碳酸钙晶体的生长。研究结果表明:HPG-COOH可以有效的控制碳酸钙从无定形纳米粒子到无定形空心球,最后转变为霰石相碳酸钙空心球。通过高分辨透射电镜和选区电子衍射分析,我们发现这是一个非经典结晶过程。得到的霰石相碳酸钙空心球具有“膨胀蒲公英”状的外观形貌,即空心球的壳层是由与球表面垂直的片状霰石相介晶堆叠构成。空心球壳层的截面使我们联想到了贝壳的微结构——片状的碳酸钙晶体之间层层堆砌在一起。以上结果揭示了晶体生长调控剂的拓扑结构对生物矿化过程的影响,以及非经典结晶过程对于构筑多级微结构的重要作用。4.利用HPG-COOH中粘合/助溶链段摩尔比调控碳酸钙结晶双亲水嵌段共聚物是一种新近出现的结构简单的晶体生长调控剂。这类大分子中的一个链段与无机矿物表面发生强烈相互作用,称为粘合链段;另一部分与矿物表面作用很弱,主要起分散稳定的作用,称为助溶链段。据此,我们改变HPG端基的羟基转化率,得到了一系列具有不同粘合/助溶链段摩尔比(the mole ratio of the interacting to stabilizing portion, RI / S)的晶体生长调控剂,并研究了它们对碳酸钙结晶的影响。结果表明:随着RI / S从0.1逐渐增加到0.9,碳酸钙晶体的外貌从松塔状,变为橄榄状,最后变为高度单分散的碳酸钙微球。同时随着RI / S的增大,碳酸钙的晶型也从方解石相转化为霰石相。我们此外还研究了RI / S值分别为0.3,0.6,0.7的HPG-COOH浓度变化对碳酸钙结晶的影响。结果表明RI / S值为0.3时,随着浓度从0.5 mg/mL增大到2 mg/mL,碳酸钙晶体的形貌从花生状,橄榄状最后变为短棒状和球状的混合物,产物中霰石相的含量也随浓度升高而增大。对于RI / S值为0.6和0.7的HPG-COOH,浓度升高导致霰石相单分散微球的尺寸略减小。更多还原

【Abstract】 Hyperbranched polymers are a novel kind of three dimensional torispherical irregular macromolecules possessing highly branched architectures, many inner cavities and a large amount of terminal functional groups. Due to their unique molecular structures and properties, hyperbranched polymers have become the hot topics in many research fields. Up to now, great progresses have been made in the synthesis, characterization, modification, and application of hyperbranched polymers. On the basis of the previous works, this thesis focuses on the synthesis and modification of hyperbranched polymers through the reversible addition fragmentation chain transfer polymerization or a simple esterification to endow the hyperbranched polymers with new properties. The resulting hyperbranched polymers were applied to construct micro/nano structures, including the self-assembly of hyperbranched polymers into micelles, the construction of microporous films by the breath figure method and biomineralization mediated by hyperbranched polymers. The detailed results were described as follows.1. pH-responsive self-assembly of carboxyl-terminated hyperbranched polymers.The hydroxyl terminal groups of hyperbranched polymers (HBPO-OH) were replaced by carboxyl groups by a simple esterification and the obtained carboxyl-terminated hyperbranched polymers (HBPO-COOH) displayed a pH-responsive self-assembly behavior in solution. HBPO-COOH existed as unimolecular micelles at high pH (pH=12.21) due to the ionization of carboxyl groups, while the polymers aggregated into multimolecular micelles from 10 to 500 nm with the decrease of pH as a result of the partial protonation of the carboxyl groups. The size of the obtained micelles depended strongly on the solution pH, the lower the pH, the bigger the micelles. TEM, DLS, ATR-FT-IR, 1H NMR and AFM measurements substantiated that the multimolecular micelles were formed by the secondary aggregation of unimolecular micelles driven by the hydrogen bonding interaction depending on the solution pH.2. Honeycomb-structured microporous films made from hyperbranched polymers by the breath figure method.Honeycomb-structured microporous films were self-assembled from a new type of multiarm copolymer, hyperbranched poly(3-ethyl-3-oxetanemethanol)-star-polystyrene (HBPO-star-PS). The precursor consisting of an HBPO core and a number of PS arms was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The microporous film was prepared by the evaporation of a chloroform solution of the precursor in a humid atmosphere (the so-called breath figure method). Compared to our former work, the hexagonally packed pores in the film were not interpenetrated and isolated from one another by the walls. The size of the pores could be controlled easily by changing the casting volume of the solution, the molecular weight and the concentration of the polymer, and so forth. The water contact angle on the film surface indicated that the hydrophobicity of the film surface was significantly enhanced as a result of the formation of the porous structure.3. Bioinspired synthesis of calcium carbonate hollow spheres with a nacre-type laminated microstructure.We combine the characters of hyperbranched polymers and the concept of double-hydrophilic block copolymer (DHBC) to design a 3D crystal growth modifier, HPG-COOH. The novel modifier can efficiently control the crystallization of CaCO3 from amorphous nanoparticles, amorphous hollow spheres to vaterite hollow spheres by a nonclassical crystallization process. The obtained vaterite hollow spheres have a special puffy dandelion-like appearance; that is, the shell of the hollow spheres is constructed by platelet-like vaterite mesocrystals, perpendicular to the globe surface. The cross-section of the wall of a vaterite hollow sphere is similar to that of nacres in microstructure, in which platelet-like calcium carbonate mesocrystals pile up with one another. These results reveal the topology effect of the crystal growth modifier on biomineralization and the essential role of the nonclassical crystallization for constructing hierarchical microstructures.4. Control the CaCO3 crystallization in vitro through the molar ratio of the interacting/stabilizing portion (RI / S) in a hyperbranched polymer.Double hydrophilic block copolymers (DHBCs) often consists of one hydrophilic block designed to interact strongly with the appropriate inorganic minerals and surfaces, and another hydrophilic block that does not interact (or only weakly interacts), and mainly promotes solubilization in water. An effective DHBC should be an optimized molecular design combining the advantages of electrostatic particle stabilization with those of steric particle stabilization, so we changed the functionalization efficiency for the carboxyl groups coupled on the surface of HPG and synthesized a series of HPG-COOH with different ratios of the interacting to stabilizing portion (RI/S). We investigated the influence of the RI/S value on the morphology and crystal habit of the obtained CaCO3 by the one-pot precipitation and found that as the RI/S value increased from 0.1 to 0.9, the morphology of CaCO3 changed from pinecone-like, olive-like to highly monodisperse spheres and the phase transition occurred from pure calcite, a mixture of calcite and vaterite to pure vaterite. We also investigated the concentration effect of HPG-COOH with RI/S value 0.3, 0.6, 0.7 on CaCO3 crystallization. For HPG-COOH0.3, as the concentration increased from 0.5 mg/mL to 2 mg/mL, the morphology changed from peanut-like, olive-like to a mixture of sticks and spheres, the vaterite content also increased accordingly with the increasing of the concentration. For HPG-COOH0.6 and HPG-COOH0.7, the increasing of concentration resulted in the decreasing of the size of the highly monodisperse vaterite spheres.更多还原