高分子专业英语课件

1、 Polymerisation is a process which allows simple low molecular weight compounds to combine and forms a complex high molecular weight compound.Addition（Chain）Polymerisation This type of polymerisation is characterised by a self-addition of the monomer molecules, rapidly through a chain reaction. The

2、product has the same composition as that of the monomer molecules. In this reaction no byproduct is formed. Since the compounds containing reactive double bonds, therefore, can proceed by a chain reaction mechanism.Typical examples: Olefines (CH2=CHR) Ethylene -CH2=CH2Propylene- CH2=CH-CH3Isobutylen

3、e- CH2=C(CH2)2Dienes (CH2=CR-CH=CH2)Isoprene- CH2=C-CH3- CH=CH21, 3-Butadiene- CH2=CH-CH=CH2Chloroprene- CH2-CH-CCl=CH2Free-Radical Addition Polymerisation The polymer chain is initiated by free radicals produced by the decomposition of compounds called initiators Initiators : The initiators are the

4、rmally unstable compounds. When energy is supplied, they decompose into two identical fragments by homolytic decomposition. Each fragment carries one unpaired (lone) electron with it; and called free radicals. Free-radicals are also formed when initiators are induced by suitable catalysts. The decom

5、position of hydrogen peroxide by a ferrous ion and hydroperoxide by a cobaltous ion are the examples of initiators, decomposed by reduction-oxidation (redox) reaction. Polymerisation reactions using these redox initiators are termed as redox polymerisation,Initiation: A free-radical contains an unpa

6、ired electron; which always search a lone electron to couple with and get stabilised itself. Free-radical is, therefore, highly reactive species which attacks the double bond in the monomer molecule in such a manner: After initiation step, the propagation step get started, where the free-radical sit

7、e at the first monomer unit attacks the double bond of a fresh monomer unit. Thus, the second monomer molecule links with the first and the transfer of the radical site from the first monomer molecule to the second takes place by the unpaired electron transfer process as shown below: This chain agai

8、n contains a radical site at its end carbon atom and can attack another monomer molecule with a transfer of the radical site to the new monomer molecule as follows: where n denotes the monomer molecules added in the chain growth. In the growing chain , the mode of the addition of monomer molecule ca

9、n be of the head-to-tail, head-to-head , tail-to-head or tail-to-tail type. Suppose, the -CH2 - is the head and -CHX- is tail part ofa monomer unit, the four types of propagation can be shown as :Chain transfer There is another method of chain termination, which takes place by the transfer reaction.

10、 In this reaction, the growth of one polymer chain is deactivated and gets stopped, meanwhile, there is a generation of a new free-radical which starts a new polymer chain growth. The transfer reaction occurs by the abstraction of a H-atom or some other atom present in the system. This process follo

11、ws as: Ionic Polymerisation The ionic polymerisation is divided into two categories: (i) Cationic polymerisation (ii) Anionic polymerisationCationic Polymerisation In this type of polymerisation, initiators and monomers are used during the chaingrowth; however, the initiation is done by a proton and

12、 the propagation carried out by acarbonium ion. In cationic polymerisation, the initiators used are strong Lewis acids such asBF3, SnCl4, TiCl4, AlCl3 and are called catalysts. The monomers, which can undergo for this purpose are styrene, methyl styrene, many vinyl ethers and isobutylene.Anionic Pol

13、ymerisationIn anionic polymerisation, a negatively charged ion attacks onelectron pair of the monomer molecule and pushing it as far away as possible, i.e., to the end of the molecule.Simultaneously. it forms a sigma bond with the monomer unit.At the same time, a carbanion is also formed. This is re

14、presented as follows:The anionic polymerisation is represented as :In this case the initiators used are generally the organo-alkali compounds such as ethyl sodium, butyl lithium, triphenyl methyl potassium. Similarly, alkali metal amides,hydroxides and alcoxides can also be used for the anionic poly

15、merisation process.Coordination PolymerisationIn coordination polymerisation reactions the monomer molecules used are generally dienes and olefines. These reactions are catalysed by organo-metallic compounds. In such polymerisation, a monomer-catalyst complex is formed between the monomer and organo

16、metallic compound. A coordination bond is used between a carbon atom of the monomer and the metal atom of the catalyst, thus formation of monomer-catalyst complex takes place. The polymerisation process proceeds as follows:PolycondensationIn polycondensation, the reaction proceeds between monomers c

17、ontaining two or more reactive functional groups (e.g., hydroxyl, carboxyl and amino) condensing with each other.The main features regarding polycondensation are:(i) To proceed the polymerisation, monomers should have two reactive functional groups.(ii) The polymerisation takes place by step-wise re

18、action between reactive functional groups.(iii) Only one type of reaction (e.g., condensation reaction in this case) between two functional groups is brought about in polymer formation.(iv) The polymer formed still consists of both the reactive functional groups at its chain end, this is active and

19、not dead, as in chain polymerisation.Polyaddition PolymerisationIn polyaddition polymerisation, atoms are migrated from one monomer molecule to another. The monomer pairs with reactive functional groups can undergo polyaddition polymerisation.In the polyaddition reaction a pair of monomers containin

20、g reactive functional groups forms a polymer, without liberating any simple molecule in the following manner:Ring-Opening PolymerisationThe ring-opening polymerisation can be involved in the monomers of ethylene oxide (an heterocyclic oxirane ring compound) and sodium methoxide (dissolved in dioxane

21、).In the initiation step, sodium methoxide molecule attacks on oxirane ring and cleaves it into anion :After initiation, propagation starts. This step is brought about by the anion attacking a fresh ethylene oxide ring which will be opened up and added on with the simultaneous formation of an anion,

22、 thus this process goes on.After propagation, the termination step started, where HCI is added. HCI donates a proton to the anion molecule as follows : When a single monomer or a single monomer pair is polymerised and form a polymer,the process is called homopolymerisation.On the other hand, two or

23、more monomers or monomer pairs are polymerisedsimultaneously, the polymer is composed of more than one repeat unit, hence termed ascopolymerisation. The example of such reaction is styrene-butadiene rubber (SBR), the first synthetic made rubber, and is a copolymer of I, 3-butadiene and styrene which

24、 can be,formed in the ratio of 3 : 1in the presence of sodium as : In Buna-S, Bu stands for butadiene; Na for sodium and 5 stands for styrene. This copolymer is obtained by the free-radical polymerisation and composed of both butadiene as well as styrene repeat units. The copolymerisation can be dis

25、cussed under following types of polymerisation reactions:Under steady-state conditions, and assuming that the radical reactivityis independent of chain length and depends only on the nature of theterminal unit, the rate of the consumption of M I ,M2 from the initial reaction mixture is then: The cop

26、olymer equation can then be obtained dM1 I d M2 =(M1 / M21) r1 MI + M2 / (M1 +r2M2)Kll /K12 = r1 ，K22/K21 =r2 The quantities r1 and r2 are the relative reactivity ratios defined as the ratio of the reactivity of the propagating species with its own monomer to the reactivity of the propagating specie

27、s with the other monomer.Monomer Reactivity Ratio In a given reaction mixture, the amount of each monomer of the chain can be calculated by the copolymer equation. This equation suggest that if the monomer MI is more reactive than M2, the MI will enter in the copolymer more quickly. The equation is

28、then an expression which relates to the reaction mixture composition at any given time. If the copolymerisation is to- be completely understood, it is necessary to obtain a reliable values of r for each pair of monomers. By analysing the composition of the copolymer from a number of monomer (comonom

29、er) mixtures with various MI / M21 ratios, the values of r can be achieved. If FI and F2 are mole fractions of monomers MI and M2 being added to the growing chain, and fl and f2 are the corresponding mole fractions of the monomers in the reaction mixture, then the copolymer equation can be written a

30、s: which is a linear form of equation (a), and was given by Finemann and Ross. A plot between f (1- F)/F and (/2 IF) then must be linear and yield r1 from the slope and r2 from intercept.聚合是一个过程,允许简单的低分子量化合物结合,形成一个复杂的高分子量化合物加成（链）聚合反应这种类型的单体的聚合反应的特点是一个self-addition分子,通过连锁反应迅速。该产品具有相同的成分单体的分子。在这个反应没有形

31、成副产品。自包含活性双键化合物,因此,可以通过连锁反应继续进行机制。链烯烃(CH2 =装备)乙烯- - - - - -CH2浓度减少丙烯- - - - - - CH2 = CH-CH3异丁烯- - - - - - CH2 = C(CH2)2二烯烃(CH2 = CR-CH = CH2)异戊二烯- - - - - - CH2 = C-CH3 - CH1、精炼厂- - - - - - - CH2 = CH-CH = CH2之间氯丁二烯-加成聚合反应包括三个重要步骤:(i)引发(2)增长(3)终止。整个过程可以由一个自由基,离子(阳碳离子或负碳离子)或配位机理。根据反应机理,在三种类型的连锁聚合引发高

32、分子链分解产生自由基的化合物称为引发剂引发剂:引发剂是热不稳定的化合物。当有能量供应时,他们均裂分解成两个完全相同的片段。每个片段携带一个未配对电子(唯一的),称为自由基。自由基也可以在引发剂由合适的催化剂诱导时形成。过氧化氢的氧化还原反应分解,由一个亚铁离子和钴离子氢过氧化物的引发剂的例子使用这些氧化还原引发剂的聚合反应称为氧化还原聚合引发:自由基包含一个未配对电子,它总是搜索一个孤立的电子对以使自身变得稳定。因此,自由基是高活性反应组分攻击单体分子中的双键 。（图）引发步骤后,自由基的增长步骤开始，位于第一个单体单元上的自由基攻击新的单体单元的双键。因此,第二单体分子和第一个连在一起完成从

33、第一单体分子到第二个的转移，发生的未配对电子转移过程如下所示（图）（图）这个过程持续攻击新单体的分子,增加链到一个接一个，知道链增长由于缺乏进一步的新的单体而结束。它的整个过程被叫做链增长，过程如下连接方式可以是 头尾，头头。链终止链终止发生在没有进一步单体分子增加的链增长之后，链终止是对活性中心聚合物的摘取，根据时间、温度、单体单元和引发剂浓度，两个增长的链在统计概率上，接近并相互碰撞。当碰撞发生时,接下来的两个反应（如图）阻止了链增长链转移还有一个链终止的方式，链转移，在转移反应中发生在这个反应,高分子链的增长是无效的和停止的,与此同时,还有一个新的自由基的产生,开始了一个新的聚合物链增长

34、。转移反应发生的H原子或其他原子提取出现在系统中现在,一项新的R自由基的生成，增长链终止。因此,R 准备引发以及新的链增长。在这里,一个链的终止增长和一个新的链的引发同时发生。自从链增长从一个点转移到另一个,这一过程被称为“链转移”。离子聚合阴离子聚合和阳离子聚合在这种类型的聚合反应中，引发剂和单体在链增长是被使用。然而，链引发引发通过一个质子和由碳正原子的增长发生 在阳离子聚合反应中，用的引发剂是强的路易斯酸，例如BF3, SnCl4, TiCl4, AlCl3，被叫做是催化剂 能用作达到这个目的的单元体有 苯乙烯 甲基苯乙烯 乙烯醚 异丁烯阴离子聚合在阴离子聚合中，电子对的单体分子对负电荷的离子的攻击，尽可能的推它远。结束的同时它形成一个键的单体单元。同时，也形成一个负碳离子。表示如下：阴离子聚合表示为：在这种情况下，引发剂一般是有机碱化合物，如乙基丁基锂，钠，钾三苯甲基。同样，碱金属氢氧化物和醇盐化合物，也可用于阴离子聚合方法。配位聚合在配位聚合反应的单体分子一般使用二烯烃和烯烃。这些反应是由有机金属化合物催化。在这样的聚合，单体催化剂配合物形成在单体和有机金属化合物之间。配位键使用的单体碳原子和催化剂的金属原子之间的单体复合物的形成，使催化剂发生。聚