【作者】 陈冰；

【导师】 梁丽芸； 谭必恩；

【作者基本信息】 华中科技大学 ， 高分子化学与物理， 2008， 硕士

【摘要】 超临界CO₂由于具有无毒、不易燃烧、环境友好、来源丰富、价格便宜以及温和的临界条件等众多优势,可作为一种绿色溶剂,应用于萃取、有机反应、纳米微粒合成、催化等领域。它既具有类似气体的高扩散性,又具有类似液体的较大密度,这些特点保证了它可以替代现今工业生产中大量使用的、通常是有毒的有机溶剂,从而明显改善由于使用有机溶剂所带来的环境污染问题。尽管超临界CO₂具有种种优势,但是它的应用却经常受到限制。这是因为CO₂的极性很弱,因而极性物质在超临界CO₂中的溶解度很小,为了增加这些物质在超临界CO₂中的溶解度,常用的解决方法是使用亲CO₂的表面活性剂。目前用于超临界CO₂的表面活性剂多是含氟或含硅的化合物,这些物质或是有毒或是不易降解、价格昂贵,所以急需寻找一种安全、环保、便宜、易降解的物质以取代上述物质。而低分子量的聚乙酸乙烯酯（OVAc）就具有上述特点,并且可以适度的溶解在超临界CO₂中。而低分子量聚乙酸乙烯酯的制备通常是对普通的聚乙酸乙烯酯（PVAc）进行萃取、分级以得到低分子量的聚合物,但是该方法效率低下、耗费时间（通常需要几天时间）,因而本文拟使用可逆加成—断裂链转移（RAFT）聚合方法来制备低分子量聚乙酸乙烯酯,并探讨影响分子量分布的种种因素,这对于扩展超临界CO₂应用领域以及探索聚合物在CO₂中的相行为理论都具有十分重要的意义。全文共分为三个部分:第一部分详细论述研究背景,并说明该研究的重要性。第二部分将探讨用于RAFT反应的链转移剂EOSPE（2-乙氧基硫代羰基-丙酸甲酯）的合成。本文采用醇钠和溴代酯反应合成EOSPE,然后用FT-IR、1H NMR等方法对获得的EOSPE进行结构表征,证明合成的产物为EOSPE。第三部分对乙酸乙烯酯（VAc）实施RAFT聚合,探讨聚合物分子量设计的可行性。考察了反应温度、链转移剂浓度、引发剂浓度对PVAc分子量及其分布的影响。采用GPC、FT-IR、¹H NMR等方法对所得产物的结构进行了详细表征。详细分析了分子量的设计值与实际值、分子量与转化率的关系,结果表明,RAFT聚合反应可以有效的控制产物分子量及分子量分布（PDI在1.2¹.3）,当增大链转移剂浓度、减小引发剂浓度、降低温度,都能使分子量分布变窄。更多还原

【Abstract】 Supercritical carbon dioxide is well known for use as a green processing solvent in chemical industry applications such as extraction, polymerization, organic reactions, biocatalysis, nanoparticle synthesis and separations, because of its low cost, nontoxicity, mild critical point, and nonflammability. Its gas-like diffusivity and liquid-like density allow replacing conventional, often noxious, solvents with supercritical CO₂.In spite of all the recognized advantages of CO₂-based technologies, their applicability is often limited by the fact that CO₂ is a poor solvent to many solutes of interests. Suitable surfactants can be used to overcome some of the limitations associated with processing species that are weakly solvated by CO₂. But the majority of systems reported so far have been highly fluorine-substituted, and the associated costs and low biodegradability may prohibit industrial-scale use in the key applications. The discovery of inexpensive CO₂-soluble materials or CO₂-philes is therefore an important challenge. OVAc is an inexpensive, high-tonnaged bulk commodity polymer which, unlike most vinyl polymers, is moderately biodegradable. OVAc has been shown to exhibit anomalously high solubility in CO₂ with respect to other vinyl hydrocarbon polymers. But the polymer is soluble only at relatively low molecular weights under conditions of practical relevance （P<300bar, T<100℃）.The method of establishing OVAc is, usually through an extraction of PVAc in supercritical fluid, time-consumed and low effective. So the study presented here is a rapid method to produce well-defined OVAc through employing reversible addition fragmentation chain transfer （RAFT） polymerization and the influence parameters of preparation OVAc is also investigated.In the first part of this work, a detail background of this thesis was reported, which provided the importance of this study.In the second part of this work, a study of the synthesis and characterization of 2-Ethoxythiocarbonylsulfanyl-propionic acid methyl ester （EOSPE） was reported, which is an effective chain transfer agent for VAc’s RAFT polymerization. In the third part of this work, the low molecular weight and well-defined poly（vinyl acetate） was prepared via RAFT polymerization, performed with the aim to possibly modify to the polymer as a surfactant in supercritical CO₂, and the influence parameters of preparation PVAc was also investigated. Topography, structure and molecular weight of poly（vinyl acetate） were examined with FT-IR、¹H NMR and GPC.更多还原