节点文献

新型嵌段共聚物的合成及自组装

Synthesis and Self-assembly of Novel Block Copolymers

【作者】 王万卷

【导师】 祝方明;

【作者基本信息】 中山大学 , 高分子化学与物理, 2010, 博士

【摘要】 本文主要包括基于点击化学的自组装偶联反应合成多嵌段共聚物的方法研究和基于ATRP和点击偶联反应的聚乙烯基复杂结构嵌段共聚物(线形-刷状两嵌段共聚物,两亲性双结晶三嵌段共聚物)的合成及其在水中自组装性质研究。一、基于自组装和点击化学的偶联反应合成多嵌段共聚物将带有反应性端基的嵌段共聚物在选择性溶剂中自组装形成核壳结构的胶束,使反应性功能端基充分暴露和富集在胶束外壳,有利于提高偶联反应的速率和效率,从而合成高分子量的多嵌段共聚物,该方法称之为“自组装偶联反应”。其结合了高分子物理和合成化学,是一种崭新的的高效率合成结构明确且分子量可控的多嵌段共聚物的方法;不过,前期研究存在活性端基对水氧极其敏感、必须准确添加的小分子偶联剂,因为偶联剂用量极少难以精确定量,以及溶剂体系、温度范围适用性窄等问题,导致偶联反应具体实施起来困难。通过对该方法的改进,本文联合自组装和点击化学,通过两端带有能进行点击反应基团的三嵌段共聚物自组装偶联反应合成多嵌段共聚物。首先将双端羟基聚环氧乙烷-b-聚环氧丙烷-b-聚环氧乙烷(HO-PEO-b-PPO-b-PEO-OH)三嵌段共聚物的端羟基分别转化为叠氮基(-N3)和炔基(-C≡CH),然后在水中将(N3-PEO-b-PPO-b-PEO-N3和HC≡C-PEO-b-PPO-b-PEO-C≡CH)等物质的量混合并自组装形成核壳胶束,其中不溶于水的PPO嵌段为核,可溶于水的PEO嵌段为壳,叠氮基和炔基则暴露和富集在壳层,在催化剂作用下发生点击偶联反应,得到?(?PEO-b- PPO-b-PEO?)n?多嵌段共聚物。本文也比较了非自组装状态下或添加小分子偶联剂或提高体系温度等因素对结果的影响,证明通过双端叠氮基和双端炔基A-B-A三嵌段共聚物在选择性溶剂中的自组装点击偶联反应,能够提高制备多嵌段共聚物的效率,是一种通用巧妙简便的方法。常温下等摩尔的HC≡C-PEO-b- PPO-b-PEO-C≡CH和N3-PEO-b-PPO-b-PEO-N3在选择性溶剂水中的胶束化能够富集和暴露炔基和叠氮基端基,从而大大提高端基偶联反应的效率。二、新型两亲性聚乙烯-b-聚甲基丙烯酸低聚乙二醇酯线形-刷状两嵌段共聚物的合成及其在水中的自组装通过一种新颖方便的路径来制备结构明确的两亲性聚乙烯-b-聚甲基丙烯酸低聚乙二醇酯[polyethylene-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PE-b-POEGMA)线形-刷状两嵌段共聚物(linear-brush diblock copolymer)。首先采用2,6-二[1-(2,6-二甲基苯基)亚胺乙基]吡啶合二氯亚铁/MAO/ZnEt2催化乙烯链穿梭聚合(chain shuttling ethylene polymerization, CSEP),在聚合过程中原位氧化制备端羟基聚乙烯(PE-OH),PE-OH与2-溴异丁基酰溴反应转化为ATRP大分子引发剂PE-Br,然后该大分子引发剂引发甲基丙烯酸低聚乙二醇酯(OEGMA)单体的ATRP,从而成功制得PE-b-POEGMA。接着通过动态光散射(DLS)、透射电镜(TEM)和扫描电镜(SEM)等技术手段研究PE-b-POEGMA在水中自组装形成的胶束形貌,结果发现在水中,PE-b-POEGMA线形-刷状两嵌段共聚物自组装形成夹心层状胶束,其中POEGMA嵌段位于外层,而结晶性的PE嵌段则处于中间。还用差示扫描量热法(DSC)研究其结晶行为。三、两亲性双结晶聚乙烯-b-聚环氧乙烷-b-聚乙烯三嵌段共聚物的合成及其在水中的自组装基于链穿梭乙烯聚合制得端羟基聚乙烯(PE-OH),其与戊炔酸酯化后变为点击偶联前驱体端炔基聚乙烯(PE-≡);研究双端羟基聚环氧乙烷HO-PEO-OH经磺酰化和叠氮取代端基改性,制备出为可进行点击偶联反应的另一前驱体双叠氮基聚环氧乙烷(N3-PEO-N3)。两种均聚物前驱体PE-≡和N3-PEO-N3在炔基和叠氮基摩尔比为1.2 : 1的投料条件下,以CuBr为催化剂,进行点击偶联反应,纯化后得到结构明确的两亲性双结晶三嵌段共聚物PE-b-PEO-b-PE。一共合成了PE嵌段分子量固定而PEO嵌段分子量不同的三种PE-b-PEO-b-PE三嵌段共聚物:PE-b-PEO2k-b-PE,PE-b-PEO6k-b-PE和PE-b-PEO8k-b-PE,它们在选择性溶剂水中自组装形成以不溶的PE嵌段为核,可溶的PEO链段弯曲成环作为壳层的花状胶束,形成的胶束的粒径随着PEO嵌段的增长而减小。并用核磁(NMR)、红外(IR)、凝胶渗透色谱(GPC)、动态光散射(DLS)、透射电镜(TEM)、差示扫描量热法(DSC)等技术手段对合成的PE-b-PEO-b-PE和中间产物的结构和自组装结构及结晶性进行了表征。

【Abstract】 This thesis consists of the following parts:1. Synthesis of multiblock copolymers by coupling reaction based on self- assembly and click chemistry.It is well known in polymer physics that A-B diblock or A-B-A triblock copolymers with a proper comonomer composition in a selective solvent can self-assemble to form polymeric core-shell-like micelles. Such a self-assembly forces and concentrates the reactive end-groups of the soluble block to stay on the periphery of each micelle, which should make the coupling or linking reaction much easier. Such a combination of polymer physics and synthetic chemistry has enabled us to develop a new methodology for the synthesis of long multiblock copolymers with an ordered chain sequence and controllable block lengths. Using such a self-assembly assisted coupling reaction, we have so far had a limited success in the preparation of multi-block copolymers by starting with A-B-A triblock copolymers terminated with two reactive end-groups. However, a commonly encountered drawback, when using multiple coupling reaction using a linking agent, is a low yield of multiblock products due to the slow and inefficient reactions between the di-ends-functionalized triblock copolymer chain ends and di-ends-functionalized linking agent. First, the addition of a right amount of linking agent to link each two of the reactive chain ends is always a problem, and insufficient or excessive amount of linking agent will reduce the linking efficiency. Second, highly efficient coupling reactions require reactive end-groups having very high activity, which are always sensitive to impurities such as moisty, carbon dioxide and oxygen. Therefore, a large amount of selective solvent for the self-assembly of triblock copolymers inevitably lose the coupling reactivities because of impurities. In addition, it is difficult to ensure that the linking agents can be dissolved by the selective solvents. As compared with linking reactions, directly self-assembly assisted coupling reaction among di-ends-functionalizaed block copolymers without linking agent should overcome above shortcomings. Click chemistry has been extensively used in polymer chemistry due to the high efficiency and technical simplicity of the reaction. Moreover, this procedure can be conducted in aqueous or organic media with little or no side reactions in a wide temperature range. Herein, we demonstrate the synthesis of multi-block copolymers by multiple coupling procedure using a combination of self-assembly and click chemistry. Di-ends-azido- terminated and di-ends-alkynyl-terminated poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers (N3-PEO-b-PPO-b-PEO-N3 and HC≡C-PEO-b-PPO-b-PEO-C≡CH) were respectively prepared and used together as the precursors for multiblock copolymer synthesis through coupling reaction by combination of self-assembly and click chemistry. The self-assembly of equimolar resultant triblock copolymers in water, a selective solvent for PEO, results in a core-shell structure with the insoluble and collapsed PPO blocks as the core and the soluble and swollen PEO blocks as the shell. The self-assembly concentrates and exposes the azido and alkynyl end-groups on the periphery. The multiple click coupling reactions between the self-assembled di-ends-functionalized triblock copolymers were performed, leading to the highly efficient formation of ?(?PEO-b-PPO-b-PEO?)n? multiblock copolymer chains. In comparison, the click coupling reaction was also presented in N, N-dimethylformamide (DMF) solution without self-assembly. It was found that the efficiency of the coupling reaction was very low and no long multi-block copolymer chains were produced.2. Synthesis and self-assembly in water of novel double-crystalline amphiphilic polyethylene-b-poly[oligo(ethylene glycol) methyl ether methacrylate] linear- brush diblock copolymer.We study the synthesis and self-assembly of a novel well-defined linear-brush diblock copolymer with linear crystalline polyethylene (PE) as the coil block and hydrophilic poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) as rod brush via a combination of chain shuttling ethylene polymerization (CSEP) and atom transfer radical polymerization (ATRP). Initially, bromine end-terminated PE macroinitiator (PE-Br) was synthesized through the esterification of 2-bromo-2- methylpropionyl bromide with monohydroxyl-terminated PE (PE-OH) which was prepared by means of CSEP with 2,6-bis[1-(2,6-dimethylphenyl) imino ethyl] pyridine iron (II) dichloride / methylaluminoxane (MAO) / ZnEt2 and subsequent in situ oxidation with oxygen. The resultant PE-b-POEGMA linear-brush diblock copolymer was synthesized by ATRP of monomethoxy-capped oligo(ethylene glycol) methacrylate (OEGMA) using PE-Br as macroinitiator. The self-assembly of the double-crystalline PE-b-POEGMA in aqueous solution were investigated by dynamic light scattering, transmission electron microscopy and cryofield emission scanning electron microscopy. It was found that, in water, a solvent selectively good for the POEGMA brush, PE-b-POEGMA chains could self-assemble to form sandwich-like micelles with the insoluble and crystallized PE blocks as the interlayer cores and the soluble and swollen POEGMA brush as the outer-layer shell. The crystallization of both PE and POEGMA blocks in self-assembled structure formed from aqueous solution was investigated by differential scanning calorimetry.3. Synthesis and self-assembly in water of novel double-crystalline amphiphilic polyethylene-b-poly(ethylene oxide)-b- polyethylene triblock copolymerNarrowly distributed polyethylene-b-poly(ethylene oxide)-b-polyethylene triblock copolymers (PE-b-PEO-b-PE) with a linear PE block were successfully synthesized by click chemistry between polymer precursors of akynyl-terminated polyethylene (PE-≡) and di-ends-azido-terminated poly(ethylene oxide) (N3-PEO-N3). PE-≡was synthesized via the esterification of pentynoic acid with hydroxyl-terminated PE (PE-OH), which was prepared using chain shuttling ethylene polymerization. N3-PEO-N3 derived from tosylation and subsequent substitution by sodium azide of dihydroxyl-terminated PEO (HO-PEO-OH). The self-assembly of three double-crystalline PE-b-PEO-b-PE samples (PE-b-PEO2k-b-PE, PE-b-PEO6k-b-PE, PE-b-PEO8k-b-PE) with different PEO block length in water were investigated by laser light scattering (LLS) and transmission electron microscopy (TEM). It was found that, in water, a solvent selectively good for the middle PEO block, PE-b-PEO-b-PE chains could form flower-like micelles with the two insoluble and crystallized PE blocks as the core and cyclic swollen PEO blocks as the shell. Differential scanning calorimetry (DSC) experiments showed that the crystallization of both PE and PEO blocks was intensely confined by the previously self-assembled structure of PE-b-PEO-b-PE in aqueous solution.

  • 【网络出版投稿人】 中山大学
  • 【网络出版年期】2011年 03期
节点文献中: 

本文链接的文献网络图示:

本文的引文网络