聚合物分子设计的原理与方法-5-26

1、高聚物分子设计 (Polymer Molecule Design ) n内容概要内容概要： 介绍聚合物分子设计的基本概念、原理和方法，重点定向聚合、嵌段聚合、接枝聚合和活性自由基聚合在高聚物分子设计中的应用n主要参考书主要参考书： 周其凤，胡汉杰跨世纪的高分子科学-高分子化学，化学工业出版社 （日本）高分子学会编 徐震春，岳传龙 译，朱洪法校高分子的分子设计，上海科学技术出版社 安智珠聚合物分子设计原理，湖南科学技术出版社聚合物分子设计学说的建立聚合物分子设计学说的建立 聚合物分子设计是现代高分子科学中最重要的研究方向之一，它是在高分子化学和物理学以及高分子材料科学的基础理论和实际应用研究的基

2、础上发展起来的一门新兴的学课 它需要用所归纳和积累起来的关于高分子结构与性质、结构与合成、性能与加工各种关系个约大量数据，包括从宏观性能到微观结构，从定性到定量，静态与动态等方面的理论和应用的丰富数据，以及从中找出内在的基本规律，并提出实现该种结构所需要的合成与加工方法及其条件。 用比较少的实验，准确地合成具有预定结构和指定性能的高分子化合物。聚合物分子设计是高分子科学和材料科学发展的必然趋势 自从十九世纪中叶至二十世纪初对天然高分子的改性以及从双烯得到了合成橡胶，从酚和醛合成了酚醛树脂，并加工成塑料来高分子材料发展得异常迅速 四十年代人造纤维的产量就超了当时羊毛的产量。五十年代塑料的产量先超

3、过了铝，随后又超了钢和锌，从六十年代开始，出现芳香族聚酰胺和芳香族杂环聚合物 聚合物分子设计学说是在二十世纪七十年初期建立和发展起来的。在这一时期高分子科学与其他基础科学(数学、物理和生物)的相互联系，相互渗透，并在科学交叉点上形成了聚合物分子设计 高分子化学和物理学以及高分子材料科学研究的不断深入，人们已经得到了大量关于聚合物的数、理资料。人们有可能借助计算机的记亿、判断和罗辑推理等性能，从事分子设计。杜邦等较大的化学工业公司已经使用调算机图象和辅助系统，设计新的化合物分子。 分子设计的概念 分子设计一词原先由美国麻省理工学院材料科学专业的霍恩.贝尔教授在世纪提出 分子设计的基本概念是为使材

4、料适其所用,在首先了解构成材料的分子化学结构和物性之间相互关系的基础上, 再根据要求合成出具有所得物性而又有特定化学结构的物质。 分子设计的其他定义分子设计的其他定义 第一种是指用计算机借助于经验或理论设计一种具特定性能的分子，也就是分子是可以设计出来的。以前未合成过，设计出的分子具有某种性质 第二种理解是从分子、电子水平上通过数据库等大量实验数据，结合现代的理论方法（如量子力学等）设计新的分子 第三种理解是依据具体作用对象，借用可靠的先进理论通过计算机图形学等技术设计出分子，设计出的分子化合物的功能。 在第一、第二种理解基础上的分子设计，设计的分子往往是同系物的结构改造，第三种分子设计能获得

5、全新结构类型的分子。 那么为什么迄今才提出高分子的分子设计呢?其中一个原因是，高分子工业以前一直是遵循着新聚合物发现 物性研究 加工技术开发 用途开发这样一条路线发展起来的，至今已开始趋于尽头 掌握了完备的测定分子量、分子量分布的方法以及微观结构的结构分析法,就能合成出单一分散的聚合物。所需序列长度的嵌段共聚物和所需支链长度的接技共聚物等物质，就是一次结构也能使分子具有数之不尽的形态。因此，高分子的分子设计显示出无限厂阔的前景定向聚合定向聚合 又称立体有择聚合、立体选择聚合，立体对称聚合或有规立构聚合，单体形成立体规整性聚合物的聚合过程。可细分为配位聚合、离子型定向聚合和自由基型定向聚合等。定

6、向催化剂有Ziegler催化剂、Natta催化剂和离子型催化剂等。 能进行定向聚合单体有-烯烃，二烯烃和烯类单体等，所得的聚合物称作定向聚合物。 聚合物分子中原子或原子团在空间的排布方式（构型）主要分两类：几何异构和光学异构(旋光异构)。前者由双键或环上的取代基在空间分布不同造成，有顺式和反式两种。后者由不对称碳原子或分子整体不对称引起。 该类聚合物或具有旋光性，或由于内消旋作用而不显光学活性。C*可采用R（右旋）或S（左旋）构型。根据R和S构型在链中分布可得有规立构链及无规立构链。前者包括由相同构型单元组成的 （如-R-R-R-R-或-S-S-S-S-） 全同立构聚合物或等规聚合物及构型交替

7、的间同立构聚合物。 形成立构规整性的基本原则在于控制链的增长步骤，这与所用催化剂、单体性质（极性及空间障碍）和反应条件有关。 自由基聚合一般没有获得定向聚合物的特效性，如采用极性溶剂、选取适宜的络合剂形成配位络合物或采用晶道聚合、模板聚合和固态聚合等方法，可实现自由基聚合得定向聚合物。 一般离子型聚合也不具有立构规整的特效性。如选用弱极性溶剂、低聚合温度、低单体浓度，也可得定向聚合物。 配位离子型聚合是单体与催化剂先形成配位络合物，进而反应生成定向聚合物的反应。所用配位催化剂也称Ziegler - Natta催化剂。嵌段聚合嵌段聚合 嵌段共聚物的主链至少由两种单体单元构成足够长的链段组成 ，常

8、见的有AB,ABA,ABAB, ABC型可以用多种机理来合成嵌段共聚物1.活性阴离子聚合活性阴离子聚合 这是工业上合成嵌段共聚物的常用方法，SBS就是一个例子常温下SBS反应出B段弹性体的性质，S段处于玻璃微区，起到物理交联 的作用温度上升到聚苯乙烯玻璃化温度以上，SBS具有流动性，可以模塑，因此SBS可称作热塑性弹性体，具有无需硫化的特点。 利用活性阴离子聚合的机理，还可以合成环氧丙烷-环氧乙烷嵌段共聚物，用于非离子型表面活性剂。 2.特殊引发剂特殊引发剂 双功能自由基引发剂可以用来先后引发两种单体聚合而形成嵌段共聚物3.力化学力化学 聚合物塑炼或高分子浓溶液进行高速搅拌，当剪切力大到一定程

9、度时，主链将断裂成链自由基。两种聚合物共同塑炼时，就形成两种自由基，两者偶合结果就成为嵌段共聚物4.通过缩聚中的交换反应通过缩聚中的交换反应 例如：聚酯和聚酰胺共热，可以形成嵌段共聚物接枝聚合接枝聚合 接枝共聚物的性能决定于主，支链的组成和长度，以及枝链数。 接枝反应的首要条件是要有接枝点。各种聚合机理的引发剂都能为接枝共聚提供活性种。例如应用引发剂化学分解，光，高能辐射等 接枝点和支链的产生方式，接枝方法大致有三类1.长出支链长出支链 先在某一大分子链中间形成活性点，该活性点再引发另一单体聚合而长出支链。接枝点可由自由基，阴离子，阳离子，配为聚合机理产生。2.嫁接支链嫁接支链 如果某一大分子

10、主链带有活性侧基，另一大分子带有活性端基，两者反应，就嫁接上支链3.大单体共聚嫁接大单体共聚嫁接 Pvc接枝聚合接枝聚合氯乙烯与聚二烯烃和二烯烃共聚物的接枝共聚物氯乙烯与聚二烯烃和二烯烃共聚物的接枝共聚物 聚丁二烯和丁二烯共聚作为氯乙烯单体接枝聚合的对象，一度吸引过人们的注意，这主要是想利用它们的高弹性。然而这类接枝产品的多数迄今尚缺乏实际意义。原因在于氯乙烯在很少量的丁二烯单体存在下就难以进行聚合 有些成就使得注意，其中包括通过接枝加入少量弹性体(二烯烃共聚物)从而大大提高PVC的韧性。由于这些弹性体的玻璃化转变温度低(-90 50)故当环境温度降低时PVC产品仍表现出高的韧性和冲击强度。这

11、样得到的高抗冲Pvc的冲击性能要比相应的弹性体与PVC的共混物为好例如通过接枝得到的聚（丁二烯-丙烯腈）-g-氯乙烯，由于含有接枝物使产物比相应的共混物在拉伸冲击强度上高出不少PVC与丁腈橡胶接枝共聚物及共混物的拉伸冲击强度 一些日本公司已向市场推出用丁二烯或丁二烯共聚物改性的硬质PVC。除了韧性和撕裂性明显改善外，有些产品在热稳定性和硬度方面亦有改进。少量聚二烯烃的存在就足以降低PVC的熔融粘度，从而改善其加工行为。甚至用液体聚丁二烯、用降解的天然橡胶和用聚氯丙烯作接枝骨架都能得到具有高抗冲性能的PVC氯乙烯在聚烯烃及其衍生物上的接枝共聚物氯乙烯在聚烯烃及其衍生物上的接枝共聚物 不少文献和专

12、利报道过烯烃聚合物及其共聚物的氯乙烯接枝共聚物。同时认为：烯烃聚合物与PVC的相容性有限，但其TG低，耐化学腐蚀，因此适合于PVC改性，特别是在提高韧性方面。由于这类接枝共聚物具有某些独特的性能。 氯乙烯和聚乙烯的接枝共聚物是硬质或半硬质的产品，具有很高的韧性及良好的拉伸强度。较低的加工温度和良好的流动性、较高的热稳定性、良好的耐化学药品和溶剂性能。其接枝度可根据氯乙烯与聚乙烯在组成的比例以及接枝反应条件来确定。 专利中报道过一种接枝共聚物，聚(乙烯-g-氯乙烯)含11(重量)的聚乙烯，在韧性、拉伸强度、伸长率、杨氏模量上比同样组成的机械共混物要好很多通过改进加工工艺，采取分批添加单体的方法可

13、生产出适用于塑料、薄膜、板材和具有高韧性与户外耐候性良好的涂料等一系列产品。活性自由基聚合活性自由基聚合活性聚合的特点：活性聚合的特点：实现自由基活性聚合的主要方法有以下三种：实现自由基活性聚合的主要方法有以下三种：Graft copolymers from ethylene oxide and styrenePSg-PEO, graft copolymers with PEO side chains Ito used a macromer technique to obtain graft copolymers with uniform side chains. They synthesiz

14、ed a graft copolymer of PS with uniform PEO side chains through copolymerization of styrene with PEO macromer They obtained PEO macromers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-vinyl benzyl chloride as terminating agent. An apparent decrease in the reactivites

15、of both poly (ethylene oxide) macromers and comonomers was ascribed to thermodynamic repulsion between the macromer and the backbone. An amphiphilic polystyreneg-v-stearyl-polyoxyethy-lene copolymer was prepared using the macromer technique 53.The graft copolymers were describedas microphase separat

16、ed and can be used in applications that require blood compatibilities and antithrombogenic properties Through copolymerization of styrene with PEO macromer, prepared by anionic polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydrofuran as initiator, followed by terminat

17、ion with methacryloyl chloride. The reactions are shown Novel graft copolymers with styrenebutadienestyrene triblock copolymer as backbone and PEO as grafts onto the polybutadiene blocks were synthesizedSynthesis of a Novel Kind of Amphiphilic Graft Copolymer with Miktoarm Star-Shaped SideChainsIntr

18、oduction In recent years, much attention is paid to the synthesis of copolymers with different compositions and chain architectures, such as linear, grafted, comb-shaped, star-shaped, hyperbranched, and dendrimeric chains with the purpose to establish architecture-property relationships in bulk and

19、in solution. Of these various architectures, the graft copolymers, especially the amphiphilic graft copolymers, are attractive materials because of their unique chemical and physical properties as well as their potential applications in drugs, bimomaterials, nanotechnology, polymer-hybrid nanocompos

20、ites, and supermolecular science.Xiaolan Luo, Guowei Wang, Xinchang Pang, and Junlian Huang*The Key Laboratory of Molecular Engineering of Polymer, State Education Ministry of China, Department of Macromolecular Science, Fudan UniVersity,Shanghai 200433, China ReceiVed January 17, 2008ReVised Manusc

21、ript ReceiVed February 21, 2008 It is well-known that controlled polymerizations such as anionic, ATRP, and RAFT are powerful tools for the synthesis of linear polymers with well-controlled molecular weight and polydispersity,and it is possible to make topological tailoring on polymer by the reactio

22、ns of anion with some functional compounds or modification of the end groups. And “click” reactions, as termed by Sharpless are widely used in polymer chemistry during the past few years due to their high specificity, quantitative yields, and near-perfect fidelity in the presence of most functional

23、groups. Therefore, it is promising to combine the click reaction with controlled polymerization methods to synthesize the graft copolymers with complex structure.Synthesis of the Amphiphilc Graft Copolymer with Miktoarm Star-Shaped Side Chain by Click Reaction A novel kind of graft copolymers compos

24、ed of the copolymers of EO and EEGE as main chains and starshaped functionalized ABC copolymers of PS-PEO-PEEGE as side chains were described. The copolymers main chains with pending functional groups were modified to azide groups first by a series of reactions, and then the coupling reaction of the

25、 azide groups on main chain with alkyne group at PEEGE chain end of miktoarm star copolymers could be easily carried out.a EF is the efficiency of alkyne group functionality, which was determined by 1H NMR analysis .b Determined by SEC, calibrated against PEO standard using 0.1 M NaNO3 as eluent. c

26、Determined by SEC using PS as standard and THF as solvent. d EF is the azidation efficiency of the bromide atoms of copolymer 7, which was determined by 1H NMR analysis . e Calculated using the known Mn of the backbone and the side chain. f Calculated by 1H NMR using the formula Mn,NMR(9) ) Mn,SEC(5

27、) + NN3 Mn,NMR(3) Y grafting, in which NN3 was the number of azide groups on the main chain (Supporting Information). g The graft efficiency was calculated according to the 1H NMR spectrum . In summary, an amphiphilic graft copolymer with welldefined star-shaped side chains was synthesized by the “g

28、rafting onto” method via combination of anionic polymerization and click reactions. The azide group functionality of the main chain and the alkyne group functionality at PEEGE chain end of the miktoarm star side chains were very high. The moderate graft efficiency in click coupling reaction was obta

29、ined due to the large steric hindrance of the miktoarm star side chain. This work provided a new way to prepare the graft copolymer with complex structure.Synthesis of 2,3-epoxypropyl-1-ethoxyethyl ether the operation was carried out in a 250mL three-neck flask with a magnetic stirrer;1.25g of TsOH

30、was added in batch to 50g (0.675mol) of Glycidol in 200mL of ethyl vinyl ether solution, the temperature waskept below 40, and 100mL of saturated NaHCO3 aqueous solution was added after the mixture was stirred for 3h. The organic layer was separated and dried with MgSO4. After filtration,the ethyl v

31、inyl ether was evaporated, the remainder was distilled under reduced pressure, and the fraction at 51/80 Pa Was collected.Preparation of the pure cyclized product as macroinitiatorSynthesis of amphiphilic graft copolymers c-PEO-g-PCLSynthesis and Characterization of Biopolymer-Based Electrical Condu

32、cting Graft Copolymers In this study, PANI was grafted onto GG to synthesize water-soluble electrical active biomaterial for the in vivo and in vitro sensor applications. In the series of studies, the reaction mechanism, crystalline and morphological features, electrical and thermal properties of th

33、e grafted product were extensively investigated. It has been expected that results would be leading to new promising conducting polymers especially for the sensor applications. The major advantage of this work is to use natural recourses and increase their utility in broader prospective bychemical m

34、odification.Ashutosh Tiwari, S. P. SinghDepartment of Engineering Materials, National Physical Laboratory, New Delhi 110012, IndiaReceived 4 March 2007; accepted 13 October 2007DOI 10.1002/app.27789Published online 23 January 2008 in Wiley InterScience (). GG is an edible carbohydrate polymer isolat

35、ed from the seeds of Cyanaposis tetragonolobus. It is a nonionic, branched-chain polymer, consisting of a straight chain of mannose units joined by linkages having -D-galactopyranose units attached to this linear chain by a linkages with molecular ratio of 1 : 2. GG is cold-water swelling biopolymer

36、, and is reported to be one of the most highly efficient water thickeners and tablet binder Polyolefins including polyethylene (PE), polypropylene (PP), poly(1-butene), poly(1-octene), poly(4-methyl-1-pentene), ethylenepropylene elastomer (EPR) andethylenepropylenediene rubber (EPDM) are the most im

37、portant commercial polymers. Due to their excellent combination of good chemical and physical properties with low cost, superior processibility and good recyclability, polyolefins find widespread applications in modern human life. However, the major drawback of polyolefins is the lack of functional

38、groups, which poses serious problems when polyolefins are used in areas where adhesion, dyeability, printability or compatibility with other polymers is paramount. As the current development of polyolefins is being centred on the enhancement of their overall performances in order to expand their app

39、lication areas, the lack of chemical functionality has become the major stumbling block. In fact, ever since the commercialization of PE and PP in the 1950s, the functionalization of polyolefins has been a very interesting research subject attracting attention from both academic and industrial commu

40、nities.The so-called polyolefin functionalization is explained as introducing polar functional groups into polyolefins. With the precondition of maintaining the desired properties of polyolefins, polyolefin functionalization confers reactivity to polyolefins, improving adhesion and compatibility bet

41、ween polyolefins and other materials, such as pigments, paints, glass fibers, metals, carbon black and most polymers. The application of polyolefins after functionalization can be extended to such areas that even involve catalyst supporting, medication, photoelectronmaterial, biomaterial, photo mate

42、rial and environmental protection, which have never been previously accessed by polyolefinsDesign and synthesis of side group-functionalized polyolefins Theoretically, the direct, random copolymerization of -olefins with functional monomers is the most straightforwardway to access side group-functio

43、nalized polyolefins.This approach has the advantages of ensuring a random distribution of the incorporated functional groups along the polyolefin chain and that the functional groups being quantitatively controllable simply by tuning the insertion efficiency of the functional monomers during copolym

44、erization Unfortunately, due to a strong complexation between the Lewis acid components (Ti, Zr, Hf, V and Al) of the transitionmetal catalysts and the non-bonded electron pairs onN, O and X (halides) of the functional monomers, which is in preference to that between the catalysts and the -electrons

45、 of the double bonds, the direct -olefin/functional monomer copolymerization usually suffers from catalyst deactivation. The development of metallocene and other single-site olefin polymerization catalysts including the less oxophilic late transition metal catalysts based on Fe, Ni, Co and Pd, has p

46、rovided new opportunities for the direct copolymerization of -olefins with functional monomers. Recently, successful copolymerizations of -olefins with various functional monomers were maneuvered by either exerting steric and electronic protection on the functional groups , or enhancing the steric h

47、indrance of the catalyst active sites, or employing the heteroatom-resistant late transition metal catalysts . In addition, in order to avoid catalyst deactivation caused by the direct copolymerization with functional monomers, an alternative approach (the reactive polyolefin intermediate approach)

48、was developedGraft copolymerization approach The graft copolymerization approach is widely used to synthesize functional polyolefin graft copolymers. Its general procedure is as follows. First, grafting sites are generated in polyolefins. The grafting site can be an initiator (or its precursor) moie

49、ty for living anionic or controlled/“living” radical polymerizations (including atom transfer radical polymerization (ATRP), nitroxide-mediated stable radical polymerization (NMP) and peroxyborane-initiated stable radical polymerization) or a chain transfer agent moiety for reversible addition-fragm

50、entation chain transfer polymerization (RAFT). Secondly, graft polymerization of functional monomer either from (in the case of the grafting site being an initiator moiety) or onto (in the case of the grafting site being a chain transfer agent moiety) the grafting sites to obtain functional polyolef

51、in graft copolymers. Combined the reactive polyolefin intermediate containing benzyl or vinylbenzene groups with butyllithium via a lithiation reaction to transform the pendant benzyl or vinylbenzene group to an initiator moiety of benzyllithium. The benzyllithium moieties in polyolefins initiated l

52、iving anionic polymerization of styrene, methyl methacrylate (MMA) and acrylonitrile (AN) to obtain polyolefins grafted by PS, poly(methyl methacrylate) (PMMA) and polyacrylonitrile (PAN), respectively Controlled/“living” radical polymerizations are even more frequently used to synthesize functional

53、 polyolefin graft copolymers due to their excellent adaptability for many polar monomers. Chung et al. ever prepared polyolefins containing alkyl-9-BBN side groups by copolymerization of -olefins with B-5-hexenyl-9-BBN over Ziegler-Natta and metallocene catalysts . In the presence of O2, the pendant

54、 alkyl-9-BBN groups in polyolefins were selectively oxidized at the aliphatic CB groups, forming peroxyborane (B-O-O-C) that initiated living radical polymerizations of various polar monomers including methacrylate and vinyl acetate . Recently, the same chemistry was extended to synthesize functiona

55、l graft copolymers possessing s-PSbackbone . The relatively new methods of controlled/“living” radical polymerization, including ATRP, NMP and RAFT, were also used to synthesize functional polyolefin graft copolymers. In 1998, Stehling reported copolymerizationof -olefins (propylene or 4-methyl-1-pe

56、ntene) with an alkoxyamine-substituted-olefin by a cationic metallocene catalyst rac-Et(H4Ind)2ZrMe+B(C6F5)4. This copolymerization incorporates functional alkoxyamine, a unimolecularinitiator of NMP, into polyolefins, allowing the synthesis of polyolefin-g-PS graft copolymers via NMP . Subsequently

57、, Mulhaupt and co-workers employed Pd-based late transition metal catalysts to copolymerize ethylene and alkoxyamine-substituted -olefins. They synthesized graft copolymers of highly branched PE grafted by PS and styreneacrylonitrile random copolymers, respectively. TEMPO (2,2,6,6-tetramethyl-1-pipe

58、ridinyloxy)-mediated stable radical polymerization was employed by Shimada and co-workers to prepare PP-g-PS graft copolymers from PP containing peroxide species generated by irradiation . The obtained PP-g-PS graft copolymers possess PS grafts with well-controlled molecular weight and narrow molecu

59、lar weight distribution Liu and Sen carried out selective bromination of an ethylenestyrene random copolymer prepared with a metallocene catalyst, introducing bromine at the benzylidene position of the styrene unit . The ethylenestyrene randomcopolymer containing benzyl bromine groups functions as a

60、 multifunctional initiator of ATRP and initiates, in the presence of CuBr and PMDETA, homopolymerizations ofMMA and styrene and block copolymerization of MMA/styrene and MMA/methacrylate (MA), respectively. Polyethylenegraft copolymers with various functional polymer grafts were synthesized . Analog