【作者】 严骏杰；

【导师】 尤业字；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2014， 博士

【摘要】 聚合物的性能不仅依赖于聚合物的化学结构与组成,同时也和聚合物的拓扑结构和序列结构密切相关。最近,可控“活性”聚合的快速发展,为聚合物拓扑结构和序列结构的构筑提供了强有力的工具,但是距离天然大分子的复杂、精密结构还有很大的差距。因此,寻找新的方法来构建拓扑结构规整、序列可控的聚合物对于高分子化学来说非常重要。本文通过精细的单体设计和选择高效的键合反应,制备了化学结构可控的功能性聚合物,并拓展这些聚合物在分子荧光成像、复合凝胶、重金属离子检测等方面的应用。论文主要研究内容分为以下五个部分：1.制备了含有二硫吡啶官能团的多嵌段共聚物,二硫吡啶侧单元数可以通过单体和链转移试剂的投料比来控制。当聚合物链中二硫吡啶单元数为1左右时,多嵌段聚合物在胺解反应后生成的A2B型中间体(A为巯基,B为二硫吡啶)可以进一步反应生成超支化聚合物。超支化聚合物结构外围的过量巯基在氧化条件下可以偶联生成凝胶,凝胶网络中的二硫键使之在还原条件下可以降解,凝胶-溶液间的转换过程是可逆的。同样,这种聚合物拓扑结构间的转换(线性聚合物-超支化聚合物-聚合物凝胶)适用于嵌段共聚物体系。2.通过精确的单体设计,利用高选择性、高活性特征反应如：巯基-甲基丙烯酸酯的迈克尔加成反应、胺基-硫代内酯的胺解开环反应、巯基-溴代马来酰亚胺的取代反应以及胺基-马来酰亚胺的加成反应,一锅法制备了ABC三序列、CBABCD四序列和DCBABCDE五序列的序列规整聚合物。此反应体系反应定量、高效,无需任何分离纯化,即可制备得到高分子量的聚合物。3.利用伯胺和硫代内酯的特征开环反应,反应过程中原位产生的巯基很好地避免了巯基氧化的问题；同时,巯基在太阳光的照射下能够生成硫自由基,进一步与硫代内酯单体末端的炔或烯发生自由基加成反应生成超支化聚合物。通过改变胺的结构和种类,可以很方便地调控聚合物的组成；此外,超支化聚合物结构外围的炔和烯能够进一步和生物巯基分子反应,得到生物相容性的超支化生物大分子。整个反应过程在自然太阳光下进行,绿色环保。4.通过迈克尔加成反应合成了不同结构的聚酰胺胺并考察它们作为量子点配体的能力及成凝胶能力。结果发现,线性聚酰胺胺是很好的成凝胶剂,但是不能与量子点结合；超支化聚酰胺胺可以很好的充当量子点配体,但是不能在DMF中超声形成凝胶；支化度较低、保留有部分线性单元的超支化聚酰胺胺既可以作为量子点配体,也可以形成凝胶。更为重要的是,量子点-聚酰胺胺杂化凝胶具有多响应性,还可以在溶液-凝胶状态下可逆的转变,并且凝胶状态下的荧光强度相比于溶液状态有所增强。5.在反应体系中没有任何荧光单元参与的条件下,通过聚合反应可生成具有强荧光特性的聚合物,反应技术不仅仅局限于RAFT,选择合适引发剂的ATRP聚合体系制备的聚合物同样有较强的荧光。通过密度泛函理论计算得知,RAFT试剂或ATRP引发剂结构中的苯环与邻位单体结构中的羰基之间的π-π相互作用是聚合物荧光的来源。用RAFT制备的PNIPAM-b-PEG温敏性嵌段共聚物有较宽的激发和发射区间,具有很高的量子产率、光稳定性及良好的生物相容性,37℃左右自组装成纳米粒子,在体外分子荧光成像中表现出很好的实验效果。更多还原

【Abstract】 The properties of polymers depend not only on their chemical structure and composition, but also on their topology and sequence. Recently, the rapid development of controlled/"living" polymerization techniques provides powerful tools for the control of polymeric topology and sequence. However, it’s still a long way to reach the level of natural biopolymers with accurate and complex structures. Therefore, finding new methods to easily construct polymers with well-defined topologies, controlled sequence is very important for polymer chemistry. In this dissertation, various functional polymers with controlled topology and sequence were successfully prepared by deliberate design of monomers and screening of specific organic reactions/polymerization methods, expanded applications in molecular imaging, hybrid gels and metal ions detection were also developed. The content of the dissertation includes following five parts:1. Multiblock copolymers containing pyridine-disulfide units were prepared by RAFT polymerization utilizing poly(trithiocarbonate)s (PTTC) as RAFT agent, the number of pyridine-disulfide unit in polymer chain could be easily tuned by initial feed ratios of monomer and PTTC. When the number was around1, aminolysis led to the generation of A2B intermediate (A is thiol group and B is pyridine-disulfide unit) and successive thiol-disulfide exchange reactions gave birth to hyperbranched polymers. The excess thiol groups on periphery of hyperbranched polymers were oxidized to form gels in the presence of oxygen, and the gels could be reversibly degraded with reductive agents such as DTT and GSH. This topology conversion from linear copolymers to hyperbranched copolymers to3D structured gels was also successful in block copolymer system.2. CBA, CBABCD and DCBABCDE sequence-ordered copolymers were successfully prepared in one-pot by deliberate design of monomers and employment of highly selective, high specific reactions such as thiol-methacrylate Michael addition reaction, amine-thiolactone ring-opening reaction, thiol-bromomaleimide substitution reaction and amine-maleimide addition reaction. These quantitative reactions were highly efficient, and high molecular weight polymers could be obtained without separation and purification.3. The aminolysis reaction of alkene/alkyne terminated thiolactones by primary amines generated in-situ an equivalent of thiol groups and decreased the possibility of thiol oxidization. Thiol groups would generate thiyl radicals under the sunlight irradiation, followed by thiol-ene/yne radical addition reaction to form hyperbranched polymers. The composition of the hyperbranched polymers could be readily tuned by different categories of primary amines. In addition, the excess alkene/alkyne groups were able to react with biomacromolecules containing thiol functionality to give biocompatible bioconjugates. The whole reaction process was involved in natural sunlight, and it was a green method.4. Poly(amido amine)s (PAAs) with different structures were prepared by Michael addition reaction to testify their performance on QD ligands and gelling abilities. It was found that linear PAAs were excellent gelling agent, but did not have good interaction with QDs; hyperbranched PAAs were perfect ligands for QDs but could not assemble into gels in DMF under ultrasound sonication; highly branched PAAs with linear units not only show excellent gelling ability but also behaved greatly as QD ligands. More importantly, HPAA-QD hybrid gels were multi-responsive with reversible transformation between gel and solution states, the fluorescence intensity at gel state was much stronger than solution state.5. Strong fluorescent polymers were prepared by polymerizations without utilization of any fluorescent matter in reaction system. It was not restricted to other polymerization techniques besides RAFT, such as ATRP. We came to the conclusion by calculation with density functional theory (DFT), as a matter of fact, the strong fluorescence of polymers resulted from the π-π interaction between benzene ring of RAFT agent and adjacent carbonyl group of monomers. The fluorescent block copolymers prepared by RAFT copolymerization of NIPAM and PEG presented very high quantum yield, high photostability and excellent biocompatibility. The copolymers assembled into nanoparticles at37℃and showed very promising results in vitro molecular imaging test.更多还原