高分子材料与工程专业英语翻译(2)

高分子专业英语选讲课文翻译资料

反应式略

Reaction (3.1) illustrates the former, while (3.2) is of the latter type. 反应（3.1）说明前一种形式，而反应（3.2）具有后一种形式。

图3.1 逐步聚合的示意图

（a） 未反应单体；（b）50%已反应；（c）83.3%已反应；(d) 100%已反应（虚线表示反应种类） Polyesterification, whether between diol and dibasic acid or intermolecularly between hydroxy acid molecules, is an example of a step-growth polymerization process. The esterification reaction occurs anywhere in the monomer matrix where two monomer molecules collide, and once the ester has formed, it, too, can react further by virtue of its still-reactive hydroxyl or carboxyl groups. The net effect of this is that monomer molecules are consumed rapidly without any large increase in molecular weight. Fig. 3.1 illustrates this phenomenon. Assume, for example, that each square in Fig. 3.a represents a molecule of hydroxy acid. After the initial dimmer molecules from (b), half the monomer molecules have been consumed and the average degree of polymerization (DP) of polymeric species is 2. As trimer and more dimer molecules form (c), more than 80% of the monomer molecules have reacted (d), DP is 4. But each polymer molecule that forms still has reactive end groups; hence the polymerization reaction will continue in a stepwise fashion, with each esterification of monomers. Thus, molecular weight increases slowly even at high levels of monomer conversion, and it will continue to increase until the viscosity build-up makes it mechanically too difficult to remove water of esterification or for reactive end groups to find each other.

聚酯化，是否在二元酸和二元醇或羟基酸分子间进行，是逐步聚合反应过程的一个例子。酯化反应出现在单体本体中两个单体分子相碰撞的位置，且酯一旦形成，依靠酯上仍有活性的羟基或羧基还可以进一步进行反应。酯化的结果是单体分子很快地被消耗掉，而分子量却没有多少增加。图3.1说明了这个现象。例如，假定图3.1中的每一个方格代表一个羟基酸分子。（b）中的二聚体分子，消耗二分之一的单体分子聚合物种类的聚合度（DP）是2。（c）中当三聚体和更多的二聚体形成，大于80%的单体分子已反应，但DP仅仅还是2.5。（d）中当所有的单体反应完，DP是4。但形成的每一种聚合物分子还有反应活性的端基；因此，聚合反应将以逐步的方式继续进行，其每一步酯化反应的反应速率和反应机理均与初始单体的酯化作用相同。因此，分子量缓慢增加直至高水平的单体转化率，而且分子量将继续增加直到粘度的增加使其难以除去酯化反应的水或难以找到相互反应的端基。

It can also be shown that in the A-A+B-B type of polymerization, an exact stoichiometric balance is necessary to achieve high molecular weights. If some monofunctional impurity is present, its reaction will limit the molecular weight by rendering a chain end inactive. Similarly, high-purity monomers are necessary in the A-B type of polycondensation and it follows that high-yield reactions are the only practical ones for polymer formation, since side reactions will upset the stoichiometric balance.

在A-A+B-B的聚合反应中也可以看到，精确的当量平衡是获得高分子量所必需的。假如存在一些但官能团杂质，由于链的端基失活，反应将使分子量减少。同样，在A-B类的缩聚反应中高纯度的单体是必要的，而且可以归结高收率的反应仅是形成聚合物的实际反应，因为副反应会破坏当量平衡。

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高分子专业英语选讲课文翻译资料

-------Stevens M P. Polymer Chemistry. London: Addison-Wesley Publishing Company, 1975. 13

UNIT 4 Ionic Polymerization

第四单元 离子聚合反应

Ionic polymerization, similar to radial polymerization, also has the mechanism of a chain reaction. The kinetics of ionic polymerization are, however, considerably different from that of radical polymerization.

离子聚合反应，与自由基聚合反应相似，也有链反应的机理。但是，离子聚合的动力学明显地不同于自由基聚合反应。

(1) The initiation reaction of ionic polymerization needs only a small activation energy. Therefore, the rate of polymerization depends only slightly on the temperature. Ionic polymerizations occur in many cases with explosive violence even at temperature. below 50℃(for example, the anionic polymerization of styrene at –70℃ in tetrahydrofuran, or the cationic polymerization of isobutylene at –100℃ in liquid ethylene ).

(1)离子聚合的引发反应仅需要很小的活化能。因此，聚合反应的速率仅对温度有较少的依赖性。在许多情况下离子聚合猛烈地发生甚至低于50℃（例如，苯乙烯的阴离子聚合反应在-70℃在四氢呋喃中，或异丁烯的阳离子聚合在-100℃在液态乙烯中）。

(2) With ionic polymerization there is no compulsory chain termination through recombination, because the growing chains can not react with each other. Chain termination takes place only through impurities, or through the addition of certain compounds such as water, alcohols, acids, amines, or oxygen, and in general through compounds which can react with polymerization ions under the formation of neutral compounds or inactive ionic species. If the initiators are only partly dissociated, the initiation reaction is an equilibrium reaction, where reaction in one direction gives rise to chain initiation and in the other direction to chain termination.

（2）对于离子聚合来说，不存在通过再结合反应而进行的强迫链终止，因为生长链之间不能发生链终止。链终止反应仅仅通过杂质而发生，或者说通过和某些像水、醇、酸、胺或氧这样的化合物进行加成而发生，且一般来说（链终止反应）可通过这样的化合物来进行，这种化合物在中性聚合物或没有聚合活性的离子型聚合物生成的过程中可以和活性聚合物离子进行反应。如果引发剂仅仅部分地离解，引发反应即为一个平衡反应，在出现平衡反应的场合，在一个方向上进行链引发反应，而在另一个方向上则发生链终止反应。

In general ionic polymerization polymerization can be initiated through acidic or basic compounds. For cationic polymerization, complexes of BF3, AlCl3, TiCl4, and SnCl4 with water, or alcohols, or tertiary oxonium salts have shown themselves to be particularly active. The positive ions are the ones that cause chain initiation. For example:

通常离子聚合反应能通过酸性或碱性化合物被引发 …… 此处隐藏：10675字，全部文档内容请下载后查看。喜欢就下载吧 ……