【作者】 刘敏；

【导师】 周年琛；

【作者基本信息】 苏州大学 ， 材料科学与工程， 2021， 硕士

【摘要】 高分子的结构决定其性能/功能的特异性。单一分子量序列精确聚合物因精确的分子量、准确的分子结构、明确的序列位置,有利于对高分子结构与性能关系的精准研究,为新型材料的制备和应用提供重要的理论依据。共轭聚合物因其刚性共平面结构、出色的热/化学稳定性以及载流子易迁移等特点,通常表现出优异的光致发光和电致发光等性能,广泛应用于有机发光二极管、太阳能电池、场效应晶体管和光电检测等领域。近年来,多种合成策略及高效点击化学方法的提出,为设计并合成单一分子量的共轭聚合物提供了良好的契机,推动了共轭聚合物体系性质与结构之间关系的研究进程。偶氮苯具有独特的光致异构化性能,是一类用途广泛的刺激响应性基团。在光照或加热条件下,受偶氮苯顺-反异构化的影响,主链偶氮苯共轭聚合物几何形状发生改变,表现出独特的刺激响应行为和光电性能,有望成为最有前途的新型光电材料之一。一维/二维(1D/2D)纳米材料因具有较大的比表面积、优异的光、电、磁学特性,在光电器件、生物医药、催化等领域展现出广泛的应用前景,一直是高分子领域的研究热点。两亲性聚合物可通过改变组成成分、单体顺序、相对长度等因素以溶液自组装的方式“自下而上”精准控制纳米粒子内部堆积和外部形貌,构建具有特殊功能的纳米材料。基于以上背景,可以发现对于含有不同功能单元的 单一分子量主链共轭聚合物的研究较少。尤其是将刺激响应基团引入共轭聚合物骨架中来探究序列与性质关系的例子更是寥寥无几。因此本文围绕序列结构与性质关系设计了不同序列的芴-偶氮苯共轭齐聚物和两亲性嵌段聚合物,详细研究了不同序列齐聚物的性质和溶液组装行为的差异。主要研究结果如下:1.精密合成了三种不同位置偶氮苯的单一分子量共轭芴-偶氮苯齐聚物,并系统研究偶氮苯位置的改变对流体力学体积、热性质和光学性质的影响(第二章)。(1)首先,通过多步反应合成了一端为叔丁基二甲基硅烷(TBS)保护的炔基,另一端为氨基的芴单体和偶氮苯单体,接着进行保护基团TBS的脱除或氨基的叠氮化,将逐步增长策略与一价铜催化的叠氮化物-炔烃环加成(CuAAC)反应相结合实现链增长,制备了具有不同位置偶氮苯的单一分子量共轭芴-偶氮苯精确序列齐聚物(4F-Azo、2F-Azo-2F及F-Azo-3F),并通过核磁共振氢谱、尺寸排阻色谱和基质辅助激光解析电离飞行时间质谱证明结构的准确性。(2)比较三种不同序列齐聚物的性能差异。研究发现,4F-Azo具有更长的流出时间,更小的流体力学体积,并且因其独特结构及较好的结晶度,热分解温度较低和玻璃化转变温度较高,同时其也具有更高的荧光量子效率和独特的光响应特性。相比于另外两种齐聚物,F-Azo-3F光致异构化过程所需能量最少,速率最快。此外,偶氮苯的引入抑制了芴衍生物的光氧化,并且抑制氧化程度与偶氮苯位置相关。实验结果和理论分析表明,偶氮苯基团的位置与共轭芴-偶氮苯齐聚物的性质变化紧密相连,该项工作为研究精确序列聚合物结构-性能关系提供了指导意义。2.精密合成了三种不同序列主链刚性,侧链含有疏水性烷基链和亲水性季铵盐的单一分子量芴-偶氮苯两亲性齐聚物,并系统研究了序列对两亲性齐聚物溶液自组装行为的影响(第三章)。(1)首先,通过多步反应分别合成了一端为叔丁基二甲基硅烷(TBS)保护的炔基,另一端为氨基的芴单体和一端为叔丁基二甲基硅烷(TBS)保护的炔基,另一端为溴的偶氮苯单体,接着进行保护基团TBS的脱除和氨基或溴的叠氮化,利用逐步增长与“CuAAC”点击反应精准控制芴及偶氮苯位置制备了三种不同序列的单一分子量芴-偶氮苯两亲性齐聚物(4F-4Azo、2Azo-4F-2Azo及4(F-Azo)),并通过核磁共振氢谱、尺寸排阻色谱和基质辅助激光解析电离飞行时间质谱证明结构的准确性。(2)比较三种不同序列两亲性齐聚物在相同条件下的自组装行为差异。研究发现两嵌段齐聚物4F-4Azo-8NH2在THF/H2O/HC1中组装成纳米纤维,而三嵌段齐聚物2Azo-4F-2Azo-8NH2和交替齐聚物4(F-Azo)-8NH2只能形成囊泡和复合胶束。结合理论计算,对组装机理进行初步探讨并提出了组装模型。利用紫外吸收和荧光发射光谱进行光响应行为研究,在紫外光照下,主链由反构型转变成顺式构型,对应偶氮苯反式吸收峰的吸光度值显著降低,组装体溶液荧光增强。在加热条件下发生回复,吸光度值上升,荧光降低。以上实验结果表明,在聚合物分子级别上进行细微的调整会显著影响聚集体的聚集状态及组装形貌,为精准探究结构-组装行为之间的关系提供重要指导价值。更多还原

【Abstract】 The structure of polymers determines its special performance and functionality.Discrete polymers with precise molecular weight,accurate chemical structure and clear sequence position are capable of accurately studying the relationship between the sequence structure and properties and providing important theoretical basis for the preparation and application of new materials.Conjugated polymers,while exhibiting excellent photoluminescence and electroluminescence properties due to their rigid coplanar structure,excellent thermal/chemical stability and high carrier migration,are widely used in the fields of organic light-emitting diodes,solar cells,field effect transistors and photoelectric detection.The various synthetic strategies and efficient click-chemistry methods that have been proposed in recent years provide a good opportunity for the design and synthesis of discrete conjugated polymers,promoting the research process of the relationship between the properties and structures of conjugated polymer systems.Azobenzene,which performs unique photo isomerization ability,is a kind of stimuli-responsive molecules with a wide range of applications.Owing to the influence of cis-trans isomerization of azobenzene,the geometric shape of the main chain of azobenzene conjugated polymers is changed when under light or heated,resulting in characteristic stimulus response behavior and photoelectric properties,which is expected to be one of the most promising innovative photoelectric materials.1D/2D nanomaterials have extensive applications in the fields of photoelectronic devices,biomedicine,catalysis and other fields due to their large specific surface area,excellent optical,electrical and magnetic properties.This has been a research hotspot in the field of polymers.The internal accumulation and external morphology of nanoparticles can be accurately controlled by changing its composition,monomer sequence,relative length and other factors to construct nanomaterials with special functions through the "bottom-up" self-assembly of amphiphilic polymers in solution.Based on the above background,it can be found that there are few studies on the discrete conjugated polymers with diverse functional building units.In particular,rare attention has been given to stimuli-responsive molecules as a π-conjugated building unit in the conjugated polymers backbone to explore the relationship between sequence and properties.Therefore,this thesis focuses on the relationship between sequence structure and properties to design fluorene-azobenzene conjugated oligomers and amphiphilic block polymers with different sequences,and study the differences in properties and assembly behavior of oligomers with different sequences in detail.The specific research contents are as follows:1.Three kinds of discrete conjugated fluorene-azo oligomers with different azobenzene positions(i.e.,sequence)were synthesized precisely,and systematically studied the effects of sequence change on hydrodynamic volume,thermal properties,and optical properties(Chapter 2).(1)Firstly,fluorene and azobenzene monomers were synthesized through a multi-step reaction,which protected by tert-butyldimethylsilane(TBS)at one end and an amino group at the other end,and then the removal of the protective group TBS and the conversion of amino acids into azides were performed.Using stepwise chain growth and Copper(Ⅰ)-Catalyzed 1,3-Dipolar Cycloaddition of Alkynes to Azides(CuAAC),three discrete fluorene-azo oligomers with π-conjugated azobenzene units at different locations of the conjugated oligofluorene backbone(named 4F-Azo,F-Azo-3F and 2F-Azo-2F)were synthesized.1H nuclear magnetic resonance,size exclusion chromatography and Matrix-assisted laser desorption/ionization time of flight mass spectrometry were used to confirm the accuracy of the structures.(2)Compare the differences in properties of three oligomers with various sequences.The research showed that 4F-Azo has a longer outflow time and smaller hydrodynamic volume.It shows a lower thermal decomposition temperature and a higher glass transition temperature due to its unique structure and better crystallinity.At the same time,4F-Azo also has higher fluorescence quantum efficiency and unique light response characteristics.Compared with the other two oligomers,the photoisomerization of F-Azo-3F requires the least energy and the rate is the fastest.In addition,the introduction of azobenzene inhibits the photooxidation of fluorene derivatives,and the degree of photodegradation inhibition is related to the position of azobenzene in the main chain.Experimental results and theoretical analysis indicated that the location of azobenzene can play a dominant role in determining the properties of fluorene-azo oligomers.Undoubtedly,this work can provide deeper insight into the structure-property relationships based on precisely sequence-defined polymer structures.2.Three kinds of amphiphilic fluorene-azo oligomers with rigid main chain,side chain containing hydrophobic alkyl chain and hydrophilic quaternary ammonium salt were synthesized precisely,and systematically studied the differences in self-assembly behavior of oligomers with various sequences(Chapter 3).(1)Firstly,fluorene and azobenzene monomers were synthesized through a multi-step reaction,which protected by tert-butyldimethylsilane(TBS)at one end and an amino group or a bromine group at the other end,and then the removal of the protective group TBS and the conversion of amino or bromine into azides were performed.Three discrete amphiphilie fluorene-azo oligomers with different sequences(named 4F-4Azo,2Azo-4F-2Azo and 4(F-Azo))were synthesized by using stepwise chain growth and "CuAAC" click chemistry to precisely control the position of fluorene and azobenzene to synthesize.1H nuclear magnetic resonance,size exclusion chromatography and Matrix-assisted laser desorption/ionization time of flight mass spectrometry were used to confirm the accuracy of the structures.(2)Compare the differences in self-assembly behavior of three kinds oligomers with various sequences under the same conditions.The research showed that diblock oligomer 4F-4Azo-8NH2 can be assembled into nanofibers in THF/H2O/HCl,while triblock oligomer 2Azo-4F-2Azo-8NH2 and alternating oligomer 4(F-Azo)-8NH2 are formed into vesicle and composite micelles.Combined with theoretical calculation,the assembly mechanism is initially explained and the assembly model is proposed.The UV-Vis absorption spectra and fluorescence emission spectra were used to study the photoresponse behavior.Under UV light irradiation,the absorption peak of the trans-isomer is significantly reduced and the fluorescence of the assembly solution intensity increases.Under the condition of heating,the absorbance value increases and the fluorescence decreases.The above experimental results showed that fine adjustments at the polymer molecular level will significantly affect the aggregation state of aggregation and the morphology of the assembly,which provided important value for accurately exploring the relationship between structure and performance of oligomers.更多还原