【作者】 钟玲；

【导师】 颜德岳； 周永丰；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 超支化多臂星型嵌段共聚物同时拥有线形聚合物以及超支化聚合物的性质,近年来对于它们的研究发展得很快。这些聚合物一般是通过活性聚合方法得到的,如阴、阳离子聚合,可控开环聚合(CROP),原子转移自由基聚合(ATRP)与可逆加成-断裂链转移(RAFT)聚合。RAFT聚合与其它“活性”自由基聚合方法相比,最突出的优越性在于单体的适用面很广,可以扩展到带官能团的单体,而且聚合条件温和,因此RAFT聚合成为制备新型嵌段聚合物和结构更复杂聚合物的强有力的研究工具。另外,与线性嵌段共聚物的自组装研究相对比,超支化聚合物的自组装研究较晚,有很多关键性问题等待我们去解决,如:探索可控合成具有各种拓扑结构超支化多臂共聚物的新方法,并研究聚合物的分子结构和组装行为的关系,细致研究组装过程中超支化共聚物的微相分离过程,获得新的组装形貌,建立新的表征方法等。基于此,本论文主要采用RAFT聚合技术合成了几种不同结构的超支化多臂星型嵌段共聚物,并研究了它们在选择性溶剂中的自组装行为。具体研究结果见如下:1.通过两步法成功合成了超支化双硫酯大分子链转移剂。首先利用超支化聚酯上的羟基与马来酸酐发生酯化反应得到端基含有双键的聚合物,然后利用聚合物末端的双键和二硫代苯甲酸发生加成反应生成超支化大分子引发剂,得到的超支化大分子带有大约16个末端二硫代基团。以超支化双硫酯为链转移剂,使用“core-first”的RAFT方法,对甲基丙烯酸N,N-二甲胺乙酯(DMAEMA)单体进行了RAFT聚合反应,得到超支化多臂星型共聚物H20-star-PDMAEMA。H20-star-PDMAEMA具有温度响应性,运用紫外分光光度计、动态光散射(DLS)对它在浓溶液中的温度响应行为进行了研究。2.以超支化双硫酯为链转移剂,偶氮二异丁氰(AIBN)为引发剂,采用RAFT活性自由基聚合方法,合成了以超支化聚酯(BoltornH20)为核,聚丙烯酸为臂的两亲性超支化多臂共聚物(H20-star-PAA),并通过紫外分光光度计、动态光散射(DLS)和透射电子显微镜(TEM)对它在水溶液中的pH响应的自组装行为进行了研究。结果表明:在稀溶液条件下,H20-star-PAA始终以单分子胶束的形式存在,随着溶液pH的降低,胶束的PAA壳层会逐步塌缩,导致胶束尺寸减小;而在浓溶液条件下,当溶液的pH较低时,单分子胶束会进一步聚集形成多分子胶束。3.利用“core-first”方法,通过连续的CROP和RAFT聚合反应,制备了一类具有交替杂化臂的超支化多臂共聚物。首先合成了带有大约32个交替羧基和二硫代基团的超支化大分子引发剂,然后在BF3 OEt2催化下,用其引发了环氧乙烷(EO)和四氢呋喃(THF)的阳离子开环聚合得到超支化星型共聚物H20-P(EO-THF),再用H20-P(EO-THF)作为大分子链转移剂,进行了甲基丙烯酸甲酯(MMA)的RAFT聚合发应,得到带有P(EO-THF)和PMMA交替臂的超支化星型共聚物。此工作也提供了一条聚合THF的简便方法,即用环氧乙烷作为促进剂,羧基作为引发剂可以直接一步就能引发环氧乙烷和四氢呋喃的阳离子开环共聚合反应。由于反应活性有很大差别,环氧乙烷首先进行聚合反应,然后再引发四氢呋喃开环聚合。4.以带有大约32个交替羧基基团和二硫代基团的超支化大分子聚合物为引发剂,通过连续的CROP和RAFT聚合制备得到了一种新的带有多条交替P(EO-THF)臂和PDMAEMA臂的两亲性超支化多臂共聚物。由于具有复杂的两亲性四嵌段结构,得到的杂臂超支化共聚物在DMF/水中能组装成具有核-壳结构的球形胶束。通过TEM,DLS和1H NMR对其自组装行为进行了研究。其可能的自组装机理为:疏水的超支化H20核心和PTHF链段聚集形成不溶的球形胶束的核心,伸展的PDMAEMA链段形成了胶束的亲水的外壳层(胶束的冠),而PEO链段被局限在不溶的胶束核心,形成胶束的内壳层。另外,得到的聚合物胶束由于具有PDMAEMA亲水的外壳,温度升高至PDMAEMA的LCST时,发生相转变行为,导致PDMAEMA链段塌缩在胶束的表面,聚合物胶束粒径减小,但由于PEO内壳层的存在,胶束不会缔合。并利用DLS, UV-Vis和1H NMR研究了聚合物胶束的相转变行为。5.以超支化双硫酯为链转移剂,AIBN为引发剂,进行聚乙二醇甲基丙烯酸酯(PEGMA)的RAFT聚合得到了超支化多臂星型聚合物刷。超支化星型聚合物刷在水中可以进行自组装形成大的球形胶束。通过1H NMR,DLS和TEM的研究,表明其自组装机理为“多胶束聚集体(MMA)”机理。疏水相互作用和分子之间的氢键是自组装的驱动力。单个超支化聚合物刷分子在疏水作用的驱动下,先形成具有核-壳结构的小胶束,然后小胶束通过二次聚集形成多胶束聚集体。超支化多臂星型聚合物刷在水中形成的球形大胶束具有温度响应行为,其相转变温度大约为92 oC。通过UV-Vis和DLS研究发现,温度升至LCST时,胶束表面的亲水基团与水分子间的氢键作用被破坏,疏水基团相互作用加强,大胶束与大胶束缔合形成更大的聚集体,发生温度响应行为。更多还原

【Abstract】 Recently, much interest has been aroused in the research of dendritic star copolymers because they have the properties of both linear polymers and dendritic polymers. These polymers are generally prepared by living polymerization, such as living cationic/ anionic polymerization, cationic ring-opening polymerization (CROP), atom transfer radical polymerization (ATRP) and reversible addition–fragmentation transfer (RAFT) polymerization. In comparison with other living radical polymerization techniques, RAFT polymerization has the advantages of utilizing versatile functional vinyl monomers and easy operations. So it becomes a powerful tool to synthesize novel copolymers with complicated architectures. In addition, the self-assembly behaviors of dendritic star copolymers is still at the very early beginning compared with that of linear polymer. There are still many key questions to resolve, such as synthesizing more dendritic star copolymers with novel structure by living polymerization, studying the relationship of the polymer molecular structure and self-assembly behaviors, carefully investigating the micro-phase separation of the dendritic star copolymer, obtaining new assemble shape and establishing new characterization methods.All the above facts lead to the origin and impetuses of this thesis. The main research work in this thesis is the synthesis of several different dendritic star copolymers as well as their self-assembly behaviors in selective solvents. The main results obtained in this thesis are as follows:1. The dendritic macroRAFT agent has been successfully synthesized by a two-step approach. The first step involved the reaction of terminal hydroxyl groups in the dendritic core with Maleic anhydride (MAh) to obtain the dendritic core with 16 terminal vinyl groups. The second step involved the reaction of double bond in the obtained dendritic core with dithiobenzoic acid (DTBA) to form the dendritic macroRAFT agent with nearly 16 dithiobenzoate groups. By the‘core-first’approach, the macroRAFT agent was used to induce the RAFT polymerization of 2-(Dimethylamino)ethyl methacrylate(DMAEMA) to obtain the dendritic multiarm copolymer of H20-star-PDMAEMA. H20-star-PDMAEMA undergoes a thermosensitive phase transitions at the LCST of PDMAEMA, and the phase transition behaviors of the polymer with a moderate concentration in water are examined by DLS and fluorescence spectroscopy.2. RAFT copolymerization of Acrylic acid initiated by fractionated dendritic polyester (Bolton H20) based macroRAFT agent was conducted to obtain a dendritic multiarm star copolymer of H20-star-PAA. The pH-responsive phase transition and self-assembly behavior of H20-star-PAA at different solution pH were also studied by using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results show that at the lower polymer concentration, the dendritic macromolecules exist as unimolcular core-shell micelles with hydrophobic BoltornH20 as the cores and swollen poly (acrylic acid) (PAA) as the shells, and the PAA shells will collapse on the surface of the micelles with decreasing the solution pH. While in the high concentration of the polymer, H20-star-PAA self-assemble into large multimolecular micelles due to the secondary aggregation of unimolecular micelles stabilized by the intermolecular hydrogen bonding at a low solution pH.3. By the‘core-first’approach, we synthesized a heteroarm star polymer with a dendritic core and multi alternating mixed polymer arms by combination of sequential CROP and RAFT polymerization. A special dendritic core with multi-alternating carboxylic acid and dithiobenzoate groups was synthesized from a dendritic polyester with 16 terminal hydroxyl groups. And then it was used to initiate the sequential CROP of tetrahydrofuran (THF) in the presence of ethylene oxide (EO) as the polymerization promoter and BF3 OEt2 as catalyst, and RAFT polymerization of methyl methacrylate (MMA). Finally, a heteroarm star copolymer with a dendritic core and multi-alternating arms of P(EO-THF) and PMMA were successfully prepared. In addition, the work also demonstrated a facile method for the ROP of THF in the presence of the polymerization promoter of ethylene oxide (EO). Carboxylic acid groups were directly used as the initiators to perform the one-step ROP copolymerization of EO and THF, where EO polymerized at an early stage and then the resulted PEO served as the macro-initiator to initiate the block copolymerization of THF by utilizing the great difference of the polymer activity between EO and THF.4. A new dendritic amphiphilic heteroarm copolymer containing multi alternating arms of P(EO-THF) and PDMAEMA on a dendritic core was synthesized by combination of sequential CROP and RAFT polymerization initiated by a dendritic macroinitiator capped with nearly 32 alternating terminal carboxyl acid and dithiobenzoate groups. The obtained mixed-arms dendritic star copolymer can self-assemble into spherical micelles with a core-shell-corona structure in mixed solvent of DMF/water. The self-assembly behavior was investigated by TEM, DLS and NMR spectrum and a possible self-assembly process is put forward. The hydrophobic dendritic H20 core and the PTHF segments associate into the hydrophobic insoluble core, and the extended PDMAEMA arms form the hydrophilic corona, while the hydrophilic PEO segments are restricted in the periphery of the hydrophobic insoluble core and form the hydrophilic shell. The obtained polymer micelles undergo a phase transitions at the LCST of PDMAEMA. During he LCST transition, the PDMAEMA chains shrike on the surface of the micelles core and are partially wrapped inside the PEO segments. Thus, the core-shell-corona structure of the micelles transformed into a core-shell structure with the PDMAEMA and PEO segments as the shell. The diameter of the micelles decreases greatly during the LCST transition, but no aggregation is found. Such a reversible phase transition behaviors of the micelles are examined by DLS and fluorescence spectroscopy.5. The dendritic copolymers with multiarm polymer brush have been successfully synthesized by RAFT of poly(ethylene glyco1)methyl ether methacrylate (PEGMA) initiated by dendritic macroinitiator. The dendritic multiarm polymer brush can self-assemble into spherical micelles in water. The self-assembly behavior was investigated by 1H NMR, DLS and TEM measurements, and a“multimicelle aggregate (MMA)”mechanism was suggested for the self-assembly process. The driving forces of aggregation are the hydrogen-bonding interactions between molecules and the hydrophobic interaction. In water, the dendritic brush polymers spontaneously self-assemble into small micelles with a core-shell structure driven by hydrophobic interaction, and then the small micelles further aggregate into larger MMAs by intermicellar interactions. The obtained polymer micelles undergo phase transitions at the LCST of PEGMA and the temperature is about 92 oC. When the solution was heated to the temperature above the LCST, hydrogen-bonding interactions between the water molecules and the PEGMA segments on the surface of the micelles were destroyed and the multimolecular micelles joined together to form the even larger aggregates driven by the increasing intermicellar hydrophobic interaction.更多还原