【作者】 麦亦勇；

【导师】 颜德岳； 周永丰；

【作者基本信息】 上海交通大学 ， 材料学， 2007， 博士

【摘要】 超支化聚合物因其独特的分子结构和物理化学性质,已成为近年来高分子科学界的研究热点。与传统的线性聚合物相比,超支化聚合物具有较低的溶液和熔体粘度、良好的溶解性、大量的末端官能团等特点。此外,超支化聚合物的合成相对简单,可以通过一步法合成。这些特点使得超支化聚合物在表面修饰、聚合物加工、生物医药、涂料等领域具有一定的应用价值。目前,超支化聚合物的研究主要集中在探索更有效的控制超支化聚合物支化度的方法以及寻找更加简单实际的合成方法从而把超支化聚合物的制备推向工业化等方面。除此以外,近两年来,超支化聚合物开始在聚合物自组装研究领域崭露头角,超支化聚合物的自组装真正体现了自然界“从不规则到规则,从无序到有序”的普遍规律,引起了科学工作者的极大兴趣。本文围绕这两个研究热点展开研究,研究内容主要包含两大部分,共五章。其中第一部分集中在第二、三章,主要介绍分子量相近且支化度不同的聚3-乙基-3-羟甲基环氧丁烷（PEHO）的合成及其物理性能的表征;第二部分包括第四、五、六章,主要阐述两亲性超支化多臂共聚醚的合成及其自组装行为研究。第二章中,我们通过阳离子开环聚合合成超支化PEHO。实验中我们发现,单体和引发剂的投料比对生成PEHO的支化度有影响,投料比越低,即引发剂用量越大,所得PEHO的支化度越高。另外,我们还发现反应温度对PEHO的支化度也有影响。在-50 oC～+30 oC的温度范围内,PEHO的支化度随反应温度的升高而增大,在10 oC以上变化趋势变小,趋向不变。根据这些结论,我们通过改变单体和引发剂的投料比以及改变聚合反应温度的方法合成了一些具有相近分子量且支化度不同的PEHO样品。第三章中,我们系统地研究了支化度对PEHO的结晶性能,热力学性能,以及自由体积等物理性能的影响。XRD和DSC等方法表明,支化度较小的PEHO相对结晶度较大,随着支化度的升高,聚合物结晶能力逐渐下降,当支化度达到40%以上时,PEHO呈无定型态。DSC表征得到的玻璃化转变温度（Tg）数据表明,Tg随PEHO支化度的增大而降低,表明支化度对PEHO的Tg影响较大。TGA测得的支化度不同的PEHO的降解温度（Td）在350 oC和360 oC之间,在实验误差范围内可以认为Td没有明显的变化,表明支化度对PEHO的Td影响不大。正电子湮没寿命谱（PALS）研究表明支化度主要影响的是PEHO的自由体积浓度,而不是自由体积尺寸。PEHO的支化度越高,自由体积浓度越大,从而使得PEHO的Tg和结晶性降低。PALS用具体的实验事实,从微观角度解释了支化度对PEHO的宏观物理性能的影响。第四章中,我们通过“一壶两步”阳离子开环聚合的方法合成了一系列具有不同亲水亲油比（RA/C）的两亲性超支化多臂共聚物PEHO-star-PPO。NMR和SEC表征证明,PPO成功地接到了PEHO核上。DSC和TGA结果表明PEHO-star-PPO共聚物的Tg和Td都随着RA/C值的增大而减小。超支化PEHO-star-PPO的自组装行为通过TEM、SEM和DLS等方法表征,结果表明不规则的超支化PEHO-star-PPO分子可以组装成规则的球形大胶束,胶束的平均直径在100纳米到300纳米之间,且随PEHO-star-PPO分子的RA/C值增大而减小。PEHO-star-PPO分子的自组装机理通过化学封端、变温红外、NMR以及高分辨TEM等实验方法研究。根据所得实验结果,我们提出了一种可能的PEHO-star-PPO分子的自组装机理,即“多胶束聚集体（MMA）”机理。这个机理认为,在疏水作用的驱动下,PEHO-star-PPO分子先聚集成尺寸较小的胶束,这些小胶束再通过胶束间作用力,比如氢键作用等,进一步聚集形成球形大胶束。第五章中,我们用“一壶两步”阳离子开环聚合的方法合成了一种平头状的两亲性超支化多臂共聚醚PEHO-star-PEO。NMR和SEC表征证明PEO成功地接到了PEHO核上。自组装研究发现,该平头状PEHO-star-PEO能够在水中组装成巨大的复合囊泡（LCVs）,其直径在10到100微米之间。巨大的尺寸为我们研究这些LCVs的形成机理及其稳定性提供了方便。通过显微镜下的实时观察,我们发现LCVs的形成是一个分级自组装过程。在连续的水合作用下,平头状PEHO-star-PEO先聚集形成囊泡,这些囊泡通过二次聚集,融合等过程形成一个亚稳定的三维囊泡堆（TDVS）,在均匀外力的作用下,TDVS会被打碎从而形成巨大的LCVs。组装过程中,平头状PEHO-star-PEO所形成的囊泡的巨大粘性起到了相当重要的作用。稳定性研究发现,影响LCV稳定的因素主要是LCV内囊泡的融合,且LCV所含的囊泡数越少,LCV越不稳定,包含大量囊泡的LCVs在无扰的情况下能够保持稳定直至溶剂完全挥发。第六章中,我们通过酰化反应和阳离子开环聚合物合成了荧光标记的PEHO-star-PEO,DNS-PEHO-star-PEO。NMR、紫外光谱、荧光光谱、SEC等表征方法证明了丹磺酰基（DNS）和PEO臂成功的接到了PEHO核上,根据实验结果,我们可以得到DNS-PEHO-star-PEO的超支化多臂分子结构。此外,我们研究了DNS-PEHO-star-PEO在THF/H2O共溶剂中随着水含量的增加而发生的自组装行为。荧光光谱分析结果表明随着水的体积百分比增大,DNS-PEHO-star-PEO的最大发射波长呈阶段性变化。TEM、DLS和荧光显微镜实验证明,这是由DNS-PEHO-star-PEO在含水量不同的THF/H2O的混合溶剂中形成的组装体的形貌发生转变造成的。DNS-PEHO-star-PEO在含水量较少的THF/H₂O共溶剂组装成小胶束,随着水量的增加,DNS-PEHO-star-PEO形成的组装体向“多胶束聚集体”转变,并最终转变成微米尺寸的聚合物大囊泡。这一独特的发现表明:可以通过丹磺酰基标记,根据其最大荧光发射波长的变化来跟踪聚合物组装体形貌的连续转变。所得的聚合物大囊泡在荧光显微镜下能够发出明显的绿色荧光,显示出清晰的囊泡结构。最后,我们通过变温紫外可见光谱测量了聚合物大囊泡的最低临界溶液温度（LCST）,得到囊泡的LCST约为20.6 oC。更多还原

【Abstract】 Hyperbranched polymers (HPs) have received considerable attention in the resent decade due to their unique molecular structures as well as their special physical and chemical properties. Compared with the traditional linear polymers, HPs possess some traits such as low solution and melt viscosity, good solubility, a large amount of terminal groups, and so on. In addition, HPs can be easily prepared through a one-step polymerization procedure. These advantages make HPs promising in the fields of surface modification, polymer processing, biomedicine, and coating etc. Recently, the researches on HPs have been focusing on two important directions. One is to explore more effective methods to control the degree of branching (DB) of HPs, and the other is to seek more convenient and practical approaches of preparing HPs and finally industrialize the synthesis of HPs. More recently, HPs have been freshly applied in the area of supramolecular self-assembly. The self-assembly of HPs, reflecting the principle of from irregularity to regularity in nature, has attracted people’s great interests. In this dissertation, we mainly focus on the researches of the synthesis, characterizations and self-assembly of HPs. The dissertation includes two primary parts of investigation contents. The first part, including Chapter 2 and 3, describes the synthesis and characterizations of a series of hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane]s (PEHOs) with a similar molecular weight and different DBs. The second part, including Chapter 4, 5, and 6, elucidates the preparation and self-assembly of amphiphilic hyperbranched multiarm copolyethers.In Chapter 2, PEHOs were prepared by the cationic ring-opening polymerization. In the experiments, we found two key factors that may influence the DB of PEHO. One is the feed ratio of monomer to initiator, and the lower the ratio, the higher the DB of the obtained PEHO. The other is the reaction temperature. In the temperature range of -50 oC～+30 oC, the DB of the prepared PEHO increases with increasing reaction temperature and inclines to be of no change when the temperature is higher than 10 oC. In terms of the conclusions, we prepared PEHO samples with a similar molecular weight and different DBs.In Chapter 3, we systematically investigated the influence of the DB on the physical properties of PEHO including crystallinity, thermodynamic properties, and free volume. X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) measurements indicate that PEHOs with a small DB are semicrystalline polymers, the crystallinity of PEHO decreases with increasing DB, and PEHO will become amorphous when DB is higher than 40%. The data of glass transition temperature (Tg) obtained by DSC show that the Tg of PEHO gradually reduces with the increase of DB. Thermal Gravimetric Analysis (TGA) indicates that DB does not evidently affect the temperature of decomposition (Td) of PEHO. Furthermore, we carried out the positron annihilation lifetime spectrum (PALS) measurement to study the effect of DB on the nanostructures of PEHO. The results show that the effects of DB mainly focus on the concentration of the free volume rather than on the size of the free volume of PEHO, and the higher the DB, the bigger the concentration of the free volume holes of PEHO, which leads to the decrease of Tg and crystallinity of PEHO. The PALS outcomes explain the influence of DB on the macroscopic physical properties of PEHO from a microscopic point of view.In Chapter 4, a series of amphiphilic hyperbranched multiarm copolyethers of PEHO-star-PPO with different hydrophile-lipophile ratios (RA/C) were synthesized by a“one-pot two-step”cationic ring-opening polymerization method. The results of Nuclear Magnetic Resonance (NMR) and Size Exclusion Chromatography (SEC) prove that PPO arms have been covalently attached to PEHO cores. DSC and TGA results show that both Tg and Td of PEHO-star-PPO copolymers decrease with increasing RA/C. The self-assembly behaviors of PEHO-star-PPO copolyethers were investigated by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), and so on. The results indicate that the ill-defined PEHO-star-PPO molecules can aggregate into large regular spherical micelles with average diameters of 100 to 300 nanometers, and the average sizes of the spherical micelles will decrease as RA/C increases. The self-assembly mechanism was explored by temperature-variable FTIR, NMR, TEM, etc. According to the obtained results, we suggest a possible self-assembly mechanism named as multi-micelle aggregate (MMA) to clarify the formation of the large micelles.In Chapter 5, a crew-cut amphiphilic hyperbranched multiarm copolyether, PEHO-star-PEO, was prepared by the“one-pot two-step”cationic ring-opening polymerization. The results of NMR and SEC confirm that PEO arms have been covalently grafted to PEHO cores. The crew-cut PEHO-star-PEO molecules can self-assemble into large compound vesicles (LCVs) with an average diameter of 46.9±17.8μm. Such big sizes provide us a unique advantage to study the three-dimensional structure as well as the dynamic behaviors of the LCVs by real-time observations with an optical microscope. Through real-time observations, we found that the formation of the LCVs is an interesting hierarchical self-assembly process. The crew-cut PEHO-star-PEO molecules first self-assemble into vesicles, then the sticky vesicles interconnect together as a result of the successive hydration and membrane fusion to form the special intermediates named as three-dimensional vesicle stack (TDVS), and finally the TDVS will transform into the giant LCVs after it is broken by external disturbances. The strong cohesion of the vesicles formed by the crew-cut PEHO-star-PEOs plays a significant role in the hierarchical self-assembly of the LCVs. The stability of the LCVs was also investigated. It was found that a key factor affecting the stability of the LCVs is the vesicle fusion. The stability of an LCV will enhance with increasing the number of the vesicles inside the LCV. If undisturbed, the LCVs containing a large number of vesicles can keep stable until the solvent volatilizes completely.In Chapter 6, we prepared fluorescence-labeled PEHO-star-PEO, DNS-PEHO-star-PEO. NMR, UV/Vis spectrometry, fluorescence spectrometry, and SEC measurements prove that the dansyl groups (DNS) and PEO arms have been covalently linked to PEHO cores, indicating the hyperbranched multiarm molecular structure of DNS-PEHO-star-PEO. Moreover, we studied the self-assembly behaviors of DNS-PEHO-star-PEO in THF/H2O solvent with increasing water content. The results obtained by fluorescence analysis, fluorescence microscopy, TEM, and DLS measurements indicate that DNS-PEHO-star-PEO molecules can aggregate into small micelles in THF/H2O solvent with a small amount of water, the small micelles will evolve into multi-micelle aggregates with increasing water content, and the multi-micelle aggregates will finally transform into giant vesicles with micron sizes. The outcomes reflect that the morphology transitions of polymer aggregates can be tracked by the fluorescence spectra of the DNS groups linked to the polymers. The green fluorescence emitted by the giant vesicles under a fluorescence microscope displays the distinct vesicle structure. Finally, the lowest critical solution temperature (LCST) of the giant vesicles, being about 20.6 oC, was measured by a temperature-variable UV/Vis spectrometer.更多还原