【作者】 罗时忠；

【导师】 吴奇； 刘世勇；

【作者基本信息】 中国科学技术大学 ， 物理化学， 2006， 博士

【摘要】 本论文主要以“环境敏感单分子胶束的制备及其相转变行为研究”为主题，运用可逆加成-断裂链转移(RAFT)的合成方法，制备了环境敏感的单分子胶束；并利用激光光散射、微量示差扫描量热、透过率测量和荧光标记等手段对这种新型单分子胶束的溶液性质进行了表征，详细研究了接枝在表面上高分链的相转变行为。 首先，合成了新型热敏两亲性超支化大分子并详细研究了它在溶液中的相转变行为。在实验上，运用RAFT聚合的技术，通过“grafting-from”的方法，制备出接枝在Boltorn型四代超支化聚酯H40表面上的聚(N-异丙基丙烯酰胺)(PNIPAM)高分子刷，可以形成多臂星状的共聚物大分子(H40-PNIPAM)。从结构上来看，这种星状的共聚物大分子可以看成是一个以疏水性的H40为核，以PNIPAM为壳的“核-壳”型单分子胶束。它集中体现了以下四个方面的特点：(1)具有类似核交联胶束的结构；(2)具有超支化大分子的形态；(3)接枝的PNIPAM链具有高分子刷的构象；(4)具有温敏性。因此这种新型两亲性超支化大分子的优势非常明显：它具有环境敏感行为，但它的结构稳定，不会像嵌段共聚物胶束那样随着外界环境的改变而被破坏结构或组成；它具备超支化大分子的各种潜在应用，比如药物载体、纳米反应器以及具有很高的反应活性等；此外，这种单分子胶束的壳层具有高分子刷的构象，可以用作研究高分子刷的理想模型；更重要的是，由于PNIPAM高分子刷是接枝在超支化大分子H40表面上，使它既不同于接枝在平面上的高分子刷，也不同于接枝在球面上的高分子刷，从而为验证高分子刷的有关理论提供了新的研究模型。 实验结果表明，在核H40上的PNIPAM高分子链的平均接枝密度为每个链占0.46 nm~2，证实PNIPAM是高分子刷的构象。通过激光光散射、微量示差扫描量热、透过率测量和荧光标记等表征手段，我们发现这种接枝在超支化大分子上的高分子刷的相转变行为分为两个阶段。而且所有表征手段所得到的结果都证实接枝在H40表面上的PNIPAM高分子刷有两阶相转变行为。当温度升高时，那些靠近核H40的内层PNIPAM高分子链在温度低于30℃(低于均聚PNIPAM的LCST)更多还原

【Abstract】 The dissertation with a title of "Preparation of Stimuli-Responsive Unimolecular Micelles and their Phase Transition Behavior" focuses on the synthesis of thermoresponsive unimolecular micelles by using reversible addition-fragmentation transfer (RAFT) process; and the thermoresponsive phase transition behavior of these novel unimolecular micelles is characterized in detail by a combination of dynamic and static laser light scattering (LLS), micro-differential scanning calorimetry (micro-DSC), and excimer fluorescence techniques.Firstly, we prepared an amphiphilic dendritic core-shell nanostructure with a temperature-sensitive shell. RAFT polymerization of N-isopropylacrylamide (NIPAM) was conducted using hyperbranched polyester (Boltorn H40) based macroRAFT agent. The resultant multiarm star block copolymer (H40-PNIPAM) exists as unimolecular micelles with hydrophobic H40 as the core, densely grafted PNIPAM brush as the shell. Therefore, the novel unimolecular micelles will have many properties, such as (1) having a structure like core-cross linked micelles, (2) with a dendritic morphology, (3) the grafting polymer chains take a polymer brush conformation, and (4) with stimuli-responsive behavior, and so on. It is well known that in aqueous solution amphiphilic block copolymers can self-assemble into micelles. The microstructure of block copolymer micelles is not static and there exists dynamic exchange between micelles and unimers, i.e., they tend to be disintegrated upon alteration of external conditions such as concentration, temperature, pH, and ionic strengths, etc. Chemical cross-linking of the micellar core or shell can lead to micelles with permanent stability. So here PNIPAM chains are tethered to the dendritic macromolecules, they can be considered as unimolecular micelles due to their structural resemblance to amphiphilic block copolymer micelles. Moreover, polymeric unimolecular micelles generally possess well-defmed chemical structures with pre-determined core size, controllable length and density of grafted chains, thus they could also serve as model systems for block copolymer micelles. At the same更多还原