【作者】 杜萍；

【导师】 江明；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2011， 博士

【摘要】 分子自组装是新型功能材料制备的一种“自下而上”的战略,同时,由于组装过程的复杂性和组装体的结构常具有多层次特点,分子自组装成为当前备受关注和充满挑战的重大科学问题之一。在过去的十多年中,我们课题组提出并发展了“非共价键合胶束(NCCM)"的概念,利用氢键相互作用系统地研究了性质互补的聚合物对的自组装行为。近年来,我们又将超分子化学中的主-客体间的分子识别作用引入到大分子自组装的领域中,不仅拓展了NCCM的研究范围,更深化了我们对非共价键在自组装中作用的认识。本论文的研究工作是在本课题组已有研究工作的基础上开展的,主要是利用主体分子环糊精(CD)和客体分子二茂铁(Fc)之间的包结络合作用,特别是其氧化-还原可逆性,在构筑具有电化学活性的超分子交联点、制备具有氧化-还原敏感性的超分子水凝胶,以及诱导聚合物胶束化等方面开展研究。本论文主要分为以下几个部分：1.具有电化学响应性的超分子交联点及其水凝胶研究一直以来,在智能聚合物水凝胶的研究工作中,大多数的兴趣都集中在温度和pH敏感性的研究,而氧化-还原响应性则很少被涉及。Fc具有可逆的单电子氧化还原敏感性,其还原态Fc分子可与p-CD形成稳定的包结络合物。在本章中,我们采用了一种简单有效的方法,即通过CD和Fc之间的包结络合作用,在CD稳定的CdS量子点(CD@QD)表面成功地引入了可聚合双键。所得超分子结构能够做为交联点与N’N-二甲基丙烯酰胺(DMA)单体共聚制备超分子杂化水凝胶(Fc-Gel),因此被称做“超分子交联点(Fc-SCL)"。Fc还赋予了该结构良好的电化学响应性。随着Fc-SCL含量的增加,Fc-Gel的力学性能有所增强。此外,该凝胶还具有良好的荧光性质。实验表明,在凝胶形成过程中,CD和Fc之间的包结络合起了关键的交联作用,因此这种凝胶是一种由超分子作用诱导的有机-无机杂化水凝胶。2.具有电化学响应性的温度／氧化双敏感水凝胶的制备在前一部分工作的基础之上,本部分研究将包结络合作用限定在量子点表面和官能化的聚合物端基上,并由此设计构建了新型的温度和电化学双敏感水凝胶。我们首先设计合成了一种新型的Fc修饰的RAFT链转移剂,并通过活性自由基聚合制备了端基带有Fc的嵌段共聚物Fc-(DMA-b-NIPAM),随后通过Fc和CD的包结络合作用将Fc-(DMA-b-NIPAM)引入到CD@QD表面,得到了星型聚合物超分子结构Fc-HIC。由于Fc的存在,该结构具有电化学响应性。对Fc-HIC溶液加热即可获得凝胶。水凝胶的形成主要依靠了PNIPAM的疏水聚集和Fc与CD的包结络合的协同作用,其“溶胶-凝胶”转变温度可通过动态流变实验获得。向凝胶中加入氧化剂K3Fe(CN)6之后,Fc被氧化成阳离子状态的Fc+,从CD空腔内脱落,导致凝胶转变为可流动的溶胶。这一凝胶解离过程同样可通过加入竞争客体分子金刚烷酰羧酸钠(ADA)来实现。由于ADA与CD的包结络合作用更强,可以取代Fc,与CD形成更稳定的络合物,从而导致凝胶的解离。凝胶的解离亦可通过流变实验确认。另一方面,这种凝胶还具有良好的温度可逆性,通过升温-降温循环,可以实现“溶胶-凝胶”的可逆转变。3.基于主客体包结络合和氢键双重作用的聚合物胶束化研究我们课题组过去研究的重点是基于单一的非共价相互作用,即氢键或包结络合作用的聚合物自组装行为,尚未涉及关于双重相互作用共同控制自组装体形貌的研究。在本部分中,我们采用含有Fc的单体(Fc-M-2)与甲基丙烯酸甲酯(MMA)共聚,并将该聚合物与含p-CD侧基的聚丙烯酸(PAA-CD)在水溶液中组装,构筑了由MMA/PAA氢键作用和Fc/CD包结络合作用双重诱导的NCCM。当聚合物中的Fc含量较高时,所得胶束呈球形,并且可以被竞争客体分子所解离。减少共聚物中Fc基团的含量,即增强包结络合作用与氢键的相对贡献,还可观察到聚合物组装体由球形胶束向三维网状结构的转变。4.基于包结络合作用构建粒子稳定的聚合物胶体的初步研究传统的维持聚合物胶体稳定性的方法是通过小分子表面活性剂或以亲溶剂的线形高分子来实现的。在本章中,我们建立了一种新型的制备粒子稳定的聚合物胶体的新途径。我们采用巯基环糊精稳定的金纳米粒子CD@AuNP来稳定疏水的聚2-丙烯酰氧乙基二茂铁甲酸酯(PFc)聚合物。在水相中,疏水性的PFc收缩聚集,由于CD与Fc之间的包结络合作用,亲水性的CD@AuNP富集在PFc疏水微区的外层,限制了PFc的进一步聚集,并形成了由CD@AuNP稳定的聚合物胶体球。DLS和TEM显示所得的胶体粒子为球形,并且大小均一,尺寸分布较窄。通过这种方法所制得的胶束粒子稳定性很好,可在水溶液中稳定存放数周。更多还原

【Abstract】 Molecular self-assembly is a "bottom-up" strategy to fabricate new functional materials. It has been considered as one of the most attractive and challenging scientific fields because of the complexity of the assembly process as well as the hierarchical structures of the resultant assemblies. In the past decade, our group first proposed and developed a new "block copolymer-free strategy" leading to "NonCovalently Connected Micelles" (NCCMs), in which self-assembly behavior of pairs of complementary polymers induced by hydrogen bonds were systematically investigated. Recently, we introduced host-guest interactions of supramolecular chemistry as the driving force for macromolecular self-assembly. This work not only opened a new research aspect of NCCM, but also helped us better understand the role of non-covalent interactions in macromolecular self-assembly. Based on the previous research work in our group, this thesis focuses on the fabrication of a electrochemically responsive "supra-crosslink" and supramolecular hybrid hydrogel, as well as polymeric micelles and colloids using the inclusion complexation between cyclodextrin (CD) and ferrocene (Fc) derivatives as the driving force. The contents of this thesis are as follows:1. Supramolecular hydrogels constructed by electrochemically responsive supra-crosslink.The majority of current research on responsive polymeric hydrogels is focusing on thermal and/or pH sensitive hydrogels, while those responsive to redox stimulus are still rare. It is known that Fc undergoes a reversible one-electron oxidation at a low potential, and this reduced-state molecule can form a stable inclusion complex withβ-CD. In this part, a novel electrochemically responsive supra-crosslink (Fc-SCL) was designed and prepared by incorporating Fc monomer (Fc-M) to the surface ofβ-CD stabilized CdS quantum dots (CD@QD) through theβ-CD/Fc inclusion complexation. A supramolecular hydrogel (Fc-Gel), which retained the fluorescent properties of QD, was successfully prepared by in situ polymerization of Fc-SCL with N,N’-dimethylacrylamide (DMA). The inclusion complexation betweenβ-CD and Fc played a crucial role during the formation of this supramolecular hybrid hydrogel, i.e. Fc-Gel. In addition, according to the results of dynamic rheology, an apparent increase of elastic modulus (G’) of Fc-Gel with increasing of Fc-SCL content was observed. 2. Dual responsive supramolecular hydrogel with electrochemical activity.Based on the results from last section, the CD/Fc inclusion complex pair has been further employed for connecting the surface of QD and well-designed block copolymers, then a novel hydrogel with both thermal and electrochemical responses was designed. For this purpose, a Fc-modified RAFT chain transfer agent was synthesized. From which, block copolymer of Fc-(PDMA-b-PNIPAM) with Fc at the end was obtained by living radical polymerization. The copolymer was introduced to the surface of QD via inclusion complexation to form a "star-shape" suprastructure Fc-HIC with electrochemical responses. Hydrogel formed when the aqueous solution of Fc-HIC was heated upon the LCST of PNIPAM. The hydrophobic aggregation of PNIPAM as well as the inclusion complexation on QD surface cooperatively contributed to the formation of hydrogel. When K3Fe(CN)6 was added, Fc was transformed to its oxidized state Fc+, then the inclusion complex was dissociated, and the hydrogel turned to sol. This transition can also be achieved by adding a competitive guest, i.e. a water-soluble adamantane derivative (ADA). Because the inclusion complexation between ADA and P-CD was much stronger than that of Fc, a new complex of ADA/β-CD formed instead of Fc/β-CD. The dissociation of the hydrogel can be further confirmed by rheology measurements. Meanwhile, this supramolecular hydrogel showed satisfactory thermal reversible sol-gel transition, which can be controlled by heating-cooling cycles.3. Polymeric micelles driven by simultaneous host-guest interaction and hydrogen bonding.Our group focused on the study of polymer micelles driven by a single kind of interaction, for example, hydrogen bond or host-guest inclusion complexation. In this section, we try to explore the morphology transition of macromolecular self-assembles governed by two kinds of non-covalent interactions simultaneously. Random copolymers were made of methyl methacrylate (MMA) and Fc-containing monomer (Fc-M-2) by ATRP. Then the copolymer self-assembled into stable NCCMs with cyclodextrin-grafted poly(acrylic acid) (PAA-g-CD) in aqueous solutions through both hydrogen bonding and inclusion complexation. With a high Fc content in the copolymer, spherical micelles were obtained and could be further dissociated by addition of a competitive guest. By decreasing the Fc content, i.e. to increase the relative contribution of hydrogen bond, the morphology transition from spherical micelle to network structure was observed.4. Polymer colloids stabilized by inorganic nanoparticles based on inclusion complexation.The conventional methods to stabilize polymer colloids are achieved by using low-molecular-weight surfactants or solvophilic linear polymers. In this part, a new way to stabilize polymer colloids was suggested by using inorganic nanoparticles. Typically, gold nanoparticles covered by CDs (CD@AuNPs) were employed. The Fc-containing hydrophobic polymer (PFc) collapsed in aqueous solution, but formed stabilized particles under the aid of CD@AuNPs as a result of inclusion complexation between Fc from the polymer and CD on the inorganic particle surface. The results of DLS and TEM measurements showed that the spherical colloid particles were uniform with a narrow size distribution. In addition, the hybrid colloids achieved by this method kept stable for several weeks without precipitation.更多还原