基于胆固醇衍生物的新型凝胶乳液的创制及其在低密度聚合物材料制备中的应用

【作者】 张雨；

【导师】 房喻；

【作者基本信息】 陕西师范大学 ， 物理化学， 2011， 硕士

【摘要】 凝胶乳液(也称高内相乳液)是在某种稳定剂存在下由分散相(内相)与连续相(外相)构成的凝胶状(Gel-like)体系。其中,分散相和连续相是两种互不相溶的溶剂。在多数情况下水为一相,不相溶的有机溶剂为另外一相。根据定义,只有分散相的体积分数大于或等于74%时(此比例对应于单分散无形变球体最密堆积时的临界体积比)所形成的凝胶状分散体系才称之为凝胶乳液。凝胶乳液被广泛应用于食品、化妆品、医药、化工产业及作为模板制备具有特殊结构或功能的材料等方面。其中,利用凝胶乳液作为模板,制备具有特殊结构或功能的材料是最重要也最受关注的关于凝胶乳液应用。以高内相乳液体系作为模板是将含有一种或多种可聚合单体的连续相引发聚合后,除去体系分散相,获得一系列多孔材料,这类材料被称为聚高内相乳液(polyHIPE),在分离介质、催化剂担载、固相有机合成、生物组织工程及可药物控释放等方面有着广泛应用。本学位论文综合评述了凝胶乳液及其应用,并在实验室之前的工作基础上,合成了五种双胆固醇衍生物,研究了它们与不同的高分子单体和水形成凝胶乳液的能力,考察了以凝胶乳液为模板,引发聚合其连续相,制备低密度聚苯乙烯的方法。具体来讲,主要包括以下两个方面：第一部分：以五种双胆固醇衍生物小分子胶凝剂作为稳定剂,三种高分子单体作为连续相,水作为分散相进行凝胶乳液实验。实验表明,在化合物用量为高分子单体的5%(w/v)时,化合物1和2可以作为稳定剂,在简单振荡下,即可以使苯乙烯及甲基丙烯酸叔丁酯分别与水形成凝胶乳液且其最高分散相体积分数至少为92%；光学显微镜测试及激光共聚焦测试均表明所形成的凝胶乳液为典型的泡沫结构(图1)；而化合物3、4、5均不能使三种高分子单体和水共混形成凝胶乳液,但化合物5可以将三种高分子单体在水中选择性胶凝。不同于传统的凝胶乳液体系所使用的表面活性剂,胆固醇衍生物在高分子单体内形成“微凝胶”区域,将分散相液滴包裹,使体系整体失去流动性形成凝胶乳液。其中,由于随着化合连接臂的增长,其分子间作用力增大,化合物5可以将三种高分子单体在水中选择性胶凝,形成物理凝胶。根据文献调研,这是第一例利用胆固醇衍生物将可聚合高分子单体进行胶凝形成凝胶乳液的报道,与已有凝胶乳液体系相比,本文中的凝胶乳液制备简单,仅需振荡即可以实现,且体系并不需要再添加其它物质(如CaCl2·2H2O)来防止“奥斯瓦尔德”效应(乳液中,较小颗粒被较大颗粒湮灭的现象)。第二部分：以不同分散相体积分数的凝胶乳液作为模板,将连续相苯乙烯引发聚合,制备得到聚苯乙烯材料。实验证明,胆固醇衍生物稳定剂的加入对苯乙烯的聚合并没有影响,且聚合结束后通过索氏提取去除材料中残留的稳定剂,室温下即可对材料进行干燥,没有造成材料的塌陷(图2)。由此可见,以胆固醇衍生物作为稳定剂不仅可以成功制备凝胶乳液且该类凝胶乳液可作为模板合成具有特殊结构的聚合物材料,而且材料纯化方法简单,常规实验条件即可以实现。并且,通过给凝胶乳液中添加致孔剂,制备得到了孔结构不同的聚苯乙烯材料,研究了致孔剂浓度对材料结构及密度等性质的影响,初步获得了制备并调节多孔低密度聚苯乙烯材料及其结构的实验条件。更多还原

【Abstract】 Gel emulsion (also referred as High Internal Phase Emulsion) consisting of water, stabilizer (or emulsifier) and oil is a gel-like disperse system with its internal-phase volume fraction exceeding 0.74, a data for the most compact arrangement of uniform, spherical droplets. Stabilizers used in preparations of gel emulsions do include surfactants and solid particles of sizes between a few nanometers to micrometers mostly. Conventionally, gel emulsions are commonly stabilized by large amounts of surfactants, about 5-50 wt%and particle-stabilized emulsions commonly phase-invert between volume fractions of 0.65 to 0.70. Gel emulsion is widely used in practice in food, cosmetics, medicine, chemical industry and as a template for the preparation of materials with special structure or functions and so on. Among them, the use of gel emulsions as templates to prepare materials with special structure or function is of the most importance, which has attracted much attention during the last few decades. High internal phase emulsion used as templates for the fabrication of highly porous materials contains one or more monomers as its continuous phase which has been polymerized in the system. And after the removal of dispersed phase, such materials, commonly known as poly(merized)HIPEs are obtained, which have proven to be useful in a variety of applications, including filtration membranes for molten metal and hot gases, catalyst carriers, scaffolds for solid phase organic synthesis, tissue engineering and so on.As a continuation of the works conducted in our group earlier, we have prepared stable W/O gel emulsions stabilized by cholesterol-based organogelators with water as dispersed phase and styrene as continuous phase at room temperature. Further investigation, including the preparation methods of low-density polystyrene and adjustment to its structures has been carried out. Specifically, it is composed of following two parts:PartⅠ:Gel emulsion experiments were conducted with five cholesterol-based organogelators, which have been specially prepared in the present work, as stabilizers, three kinds of monomer as the continuous phase, water as the dispersed phase. The results show that compounds 1 and 2 can stabilize styrene and tertiary butyl methacrylate to form gel emulsions with water, respectively, in a simple surge, with the concentrations of compounds being 5 wt%considering to the continuous phase. The highest volume fraction of the dispersed phase is 92%, at least. The optical microscopy and confocal images show that the microstructure of gel emulsions is a typical foam structure (Figure 1). Compounds 3,4 and 5 cannot stabilize three monomers and water to form a gel emulsion, but compounds 5 can gel monomers in the water, selectively. Unlike traditional gel emulsion stabilized by surfactant, cholesterol derivatives can make the monomer form "microgel" region in which dispersed droplets are packaged and get immobility. The intermolecular forces increase with the length of spacer’increasing, so compound 5 can make three monomers form physical gels in the water, selectively. According to the literature, this is the first case of using cholesterol derivatives as stabilizers to carry out gel emulsions with polymers. This kind of gel emulsion can be achieved simply and does not need to add other substances such as CaCl2·2H2O to prevent the "Ostwald" effect (the smaller particles are inclined to be particle annihilation by the larger phenomenon in emulsion), being compared with traditional gel emulsions.PartⅡ:Different dispersed phase volume fractions of gel emulsion with styrene as continuous phase were prepared and polymerized to obtain polystyrene. Implementation results show that the addition of cholesterol derivatives does not affect the polymerization of styrene. The removal of stabilizers by Soxhlet extraction and the dryness of materials at room temperature did not cause material collapse (Figure 2). Thus, the cholesterol derivatives, not only as a stabilizer gel emulsion can be successfully prepared but gel emulsions prepared can be used as template to synthesis polymer materials with special structure. The purification of the materials is simple. Furthermore, by adding porogen into the gel emulsion, polystyrenes with different pore structure were prepared and the effect of porogen concentration to the pore structure and density of materials were investigated, accessing to the experimental conditions of the preparation and adjustment of porous low-density polystyrene.更多还原