【作者】 陶伟；

【导师】 闫立峰； 张广照；

【作者基本信息】 中国科学技术大学 ， 物理化学， 2009， 博士

【摘要】 可逆加成-裂解链转移（Reversible Addition-Fragmentation chain Transfer,RAPT）自由基聚合方法因其聚合条件温和,适用单体范围广而被广泛的应用于嵌段,接枝,星形,超支化等聚合物的合成上。本文以N-异丙基丙烯酰胺（N-isopropylacrylamide,nipam）为研究对象,通过RAFT过程合成了不同支化度的超支化聚N-异丙基丙烯酰胺（poly（N-isopropylacrylamide）,PNIPAM）。考虑到PNIPAM水溶液具备低临界溶液温度（lower critical solution temperature,LCST）的内在属性及超支化聚合物在结构上赋予聚合物独特性质的特点。我们结合RAFT聚合方法及自缩聚乙烯基共聚（self-condensing of vinylcopolymerization,SCVCP）的方法合成了超支化PNIPAM,根据RAFT聚合的机理及我们合成的inimer的结构,超支化的PNIPAM存在以硫代羰基硫为端基,苄基为支化单元的结构。考虑到支化单元及端基的憎水性及超支化聚合物端基对聚合物性质的影响以及硫代羰基硫端基容易除去的特点。我们通过Micro-Calorimetric研究了不同支化度的PNIPAM憎水端基及憎水支化单元对LCST的影响。对于PNIPAM,硫代羰基硫端基在伯胺或仲胺的作用下几乎定量的生成巯基（-SH）,这使RAFT方法可以制备多巯基封端的PNIPAM。巯基在温和的条件下氧化,如氧气中,生成二硫键（-S-S-）。二硫键可以在还原剂,如锌粉,二硫代苏糖醇（DTT）的作用下还原为巯基。我们基于RAFT聚合方法制备了二硫键交联的温敏可降解水凝胶。我们发现,超支化PNIPAM在不同的条件下可以生成不同性质的凝胶。根据凝胶的尺寸,我们将其分为:宏观化学凝胶（宏观可见）,纳米凝胶（-100nm）。宏观凝胶及纳米凝胶均可以在DTT,锌粉的作用下分解。有趣的是,纳米凝胶在一定的浓度范围具有温敏可逆的溶液-凝胶（Solution toGel,sol-gel）转变性质。并且,这种性质会因为二硫键还原试剂,如DTT,的加入而消失。我们利用原子力显微镜观察了纳米凝胶的聚集形态时,不同的样品制备方法导致不同的聚集形态,通过研究温度与纳米凝胶水溶液状态的关系,我们认为不同的制备方法所观察到的聚集形貌对应纳米凝胶在水溶液中的不同状态。阳离子聚合物水凝胶是非病毒基因载体的理想候选。我们以合成核（PDMAEMA）壳（PEG）结构的聚合物为目标,设计了两种可能的方案。第一种是先合成超支化的PDMAEMA,将胺解后巯基封端的超支化PDMAEMA做为核,利用巯基亲核加成双键的性质将PEG做为壳接到核上。实验结果表明,我们设计的inimer由于离去基活性差(C_tr小),并不能有效地形成支化的PDMAEMA。另一种方案是合成具有表面活性性质的RAFT试剂,利用PDMAEMA具有LCST的性质和RAFT聚合中单体增长方式的特点,乳液法一步形成目标的核壳结构。实验结果表明,这种方法在合适的条件下能够获得PDMAEMA被交联,PEG呈舒展状态的聚合物颗粒。RAFT方法适用于乳液聚合,但传统的乳液聚合过程需要加入乳化剂以稳定胶束,乳化剂可能会使RAFT试剂不稳定,同时,残留的乳化剂将可能对聚合物性能带来不利的影响,因此不添加乳化剂的无皂乳液聚合具有很高的应用价值。我们考虑到异相体系聚合过程中所谓的“乳化”过程其本质是通过降低表面张力而使分散相能够稳定的存在,每个微小的分散颗粒内发生类似于本体聚合的过程。因此,我们采用了另外一条新颖的策略:利用超声提供能量的方式阻止颗粒的聚集。通过对动力学的观察,我们发现在超声的作用下,聚合物单体转化率的对数与时间几乎成线性关系。聚合产物保留硫代羰基基硫端基,分子量分布及多分散指数都符合活性自由基聚合的特点,但是利用核磁氢谱计算获得的分子量比GPC测得的分子量大很多。我们认为,超声作用下聚合物链的断裂和RAFT试剂的分解都有可能会产生这样的结果,并且聚合物链的断裂可能是更主要的因素。嵌段聚合物的自组装是最近几十年研究的热点,棒-线团（rod-coil）型的刚柔嵌段聚合物是比较独特的嵌段聚合物模型,其独特的组装行为也引起了人们广泛的兴趣。我们将双羟基封端的聚乙二醇（PEG）修饰成双苯胺封端,在酸性条件下与苯胺单体氧化聚合获得了rod-coil-rod结构的聚苯胺-聚乙二醇-聚苯胺（Polyaniline-PEG-Polyaniline,PANI-PEG-PANI）三嵌段聚合物。利用原子力显微镜观察发现,当在PANI-PEG-PANI的四氢呋喃溶液中加入乙醚时,聚合物组装成具有螺旋结构的纤维。根据临界封装参数的概念,我们提出了聚苯胺链段π-π相互作用形成发夹结构,乙醚诱导聚合物临界封装参数的改变而导致螺旋纤维的形成。同时,我们也观察到了临界封装参数理论中的过渡状态-棒状胶束。更多还原

【Abstract】 Reversible addition-fragmentation chain transfer（RAFT） living/control free radical polymerization is one of the most versatile methods to obtain well-defined polymers.Many novel structured polymers,such as block,graft,cyclic,star and hyperbranched polymers were synthesized conveniently by RAFT polymerization. Furthermore,the products obtained by RAFT polymerization can easily and high effectively be modified to thiol group capped polymers.Considering the unique reversible coupling and cleaving properties of thiol groups under mild redox circumstance,one can easily realized that the RAFT method should be a potential tool in application of biochemistry and bioconjunction.Aiming to get stimuli response degradable hydrogel,we focus on the well-known smart polymer-PNIPAM（poly（N-isopropylacrylamide））,whose aqueous solution behaved phase transition around its lower critical temperature（LCST）.The strategy for synthesis of the novel hydrogel is proposed as follow:firstly,we combine RAFT process and self-condensing vinyl polymerization（SCVCP） to get hyperbranched PNIPAM,then,after aminolysis of the product,the polymer capped with multi-thiols will be obtained,finally,exposing the multi-thiols end-capped PNIPAM to air,the oxidation of the thiol will lead the polymers cross-linked by disulfide bonds.The results of experiment showed that this strategy was feasible when degrees of branching of polymers are high enough.The gels obtained by this strategy were able to decompose when reduced agent,such as Zn powder and DTT were added.Furthermore,at appropriate concentration,the gels with the sizes at nanometer scale were obtained.The aqueous solutions of the nanogels behaved reversible solution to gel trasition when temperature changed,the novel properties disappeared when DTT was added,accompanied by the size of nanogels turning small. The morphologies of the nanogels on fresh mica were different according the methods of preparing:when samples were dried by heating,the fiber like aggregations would be got,while samples were dried by high speed spinning,the aggregations were clusters looked like flowers.The interesting phenomena might contribute to the different states of the nanogel solution at different temperature.Considering the novel properties of PNIPAM and the unique structure of hyperbranched branched polymer,we also investigated the influence of branched structure to the phase transition of aqueous solution of PNIPAM with Micro Calorimetric Investigation.The influences were thought to be expressed by the random distributed hydrophobic units such as benzyl dendritic uints and thiocarbonylthio terminal units.The results showed that the phase transfer temperature（Tp） of aqueous solution of PNIPAM decreased sharply when degree of branching（DB） increased.Furthermore,after thiocarbonylthio end groups were eliminated by amine,the Tp increased greatly,the bigger the DB was,the greater the increasing was.When investigating the relationship of DB and T_p of the aminolized PNIPAM,the almost linear correlation was found,and we proposed this phenomenon might be due to the independent disturbing of hydrophobic benzyl units to water layer around PNIPAM,considering the branching units were comparted by linear units.The results might imply the probability of tuning the phase transfer temperature by changing the degree of branching of hyperbranched PNIPAM.The RAFT polymerizations are also appropriate for heterogeneous systems such as emulsion polymerization and miniemulsion polymerization.Different from traditional heterogeneous systems which need emulsifiers to stabilize the dispersed oil particles,we used ultrasound to encounter the aggregation of the particles caused by the tendency of reducing surface energy.We investigated the kinetic behavior of this system,molecular weights distribution of products obtained by this method.The results showed that the molecular weight distributions and polydispersities of the products were good（PDI＜1.3） and the polymers were end capped by thiocarboylthio groups.But,further analysis showed that the molecular weights obtained by GPC were greatly smaller than the ones calculated by ¹HNMR.We attributed the results mainly to the cleavage of the polymers in ultrasonic field,Aiming to synthesizing cationic nanogel which owns PDMAEMA as core and PEG as shell,we designed two strategies.One strategy is that:firstly,synthesizing hyperbranched PDMAEMA,and then getting multi-thiol end capped PDMAEMA as a core after aminolysis,finally,grafting acrylate group modified PEG to the core to form the shell.But,experiment showed that the inimer we used was not appropriate for RAFT process of the DMAEMA monomer.The other strategy is one-step to get the target polymer by emulsion polymerization with oligomeric PEG modified RAFT agent which behaved as emulsifier.The results showed that with this help of N, N’-methylenebisacrylamide,the obtained particles owned a compacted cross-linked PDMAEMA part and an unfolded PEG part. Self-assembly of rod-coil polymers were investigated as an independent work of this dissertation.In this work,we synthesized the ABA triblock polymers,the A block was polyaniline,which is known as rigid structure for the conjugated structure of the aromatic rings,the B block was poly（ethyl glycol） which acted as a random coil in its good solvents.The block polymers,PANI_x-PEG₁₁₀-PANI_x（PEG） were found self-assembling into sphere structure in THF,which is a good solvent for PEG.When diethyl ether was added to the THF solution of the block polymer,interesting structures such as cross-like rods and helical fibers were found.The results were explained by theory of critical packing parameters if the ABA block could form a hairpin structure byπ-πstacking interaction between conjugated chains of PANI.更多还原