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。

-------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