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to allow the formation of the BF3-complex and the initiator cation according to the above reactions. However, one should not describe the water or the alcohol as a “cocatalyst”.
BF3为引发剂（异丁烯为单体），证明仅在痕量水或乙醇的存在下聚合反应是可以进行的。如果消除痕量的水，单纯的BF3不会引发聚合反应。按照上述反应为了能形成BF3-络合物和引发剂离子水或乙醇是必需的。但是不应将水或乙醇描述成“助催化剂”。
Just as by radical polymerization, one can also prepare copolymers by ionic polymerization, for example, anionic copolymers of styrene and butadiene, or cationic copolymers of isobutylene and styrene, or isobutylene and viny ethers, etc. As has been described in detail with radical polymerization, one can characterize each monomer pair by so-called reactivity ratios r1 and r2. The actual values of these two parameters are, however, different from those used for radical copolymerization.
正与自由基聚合反应一样，通过离子聚合反应也能制备共聚物，例如，苯乙烯-丁二烯阴离子共聚物，或异丁烯-苯乙烯阳离子共聚物，或异丁烯-乙烯基醚共聚物，等等。正如对自由基型聚合已经详细描述过那样，人们可以用所谓的竞聚率r1和r2来表征每单体对。然而，这两个参数的实际意义不同于那些用于自由基共聚合反应的参数。
UNIT 5 Molecular Weight and its Distributions of Polymers
聚合物的分子量及其分布
The molecular weight of a polymer is of prime importance in its synthesis and application. The interesting and useful mechanical properties which are uniquely associated with polymeric materials are a consequence of their high molecular weight. Most important mechanical properties depend on and vary considerably with molecular weight. Thus,
strength of polymer does not begin to develop until a minimum molecular weight of about 5000～ 10 000 is achieved. Above that size, there is a rapid increase in the mechanical performance of polymers as their molecular weight increases; the effect levels off at still higher molecular weights. In most instances, there is some molecular weight range in which a given polymer property will be optimum for a particular application. The control of molecular weight is essential for the practical application of a polymerization process.
对聚合物的合成和应用而言，聚合物的分子量是最重要的。聚合物材料的高分子量带来了令人感兴趣的和具有利用价值的力学性能。最重要的力学性能取决于分子量，而且随着分子量变化而发生很大的变化。因此,直到最小分于量增大到大约5 000～10 000 以后, 聚合物的强度才开始显示出来. 分子量大于这个值的时候，随着分子量的增加，聚合物的机械性能快速增加;达到更高的分子量的时候，这种效应才变平缓。在大多数情况下，对于某种特定的应用来说，某种聚合物存在着某一个分子量范围。聚合物分子量的控制对聚合过程的实际应用而言是必需的。对实际的聚合过程而言，必须控制聚合物的分子量。
When one speaks of the molecular weight of a polymer, one means something quite different from that which applies to small-sized compounds. Polymers differ from the small-sized compounds in that they are polydisperse or heterogeneous in molecular weight. Even if a polymer is synthesized free from contaminants and impurities, it is still not a pure substance in the usually accepted sense. Polymers, in their purest form, are mixture of molecules of different molecular weights. The reason for the polydispersity of polymers lies in the statistical variations present in the polymerization processes. When one discusses the molecular weight
of a polymer, one is actually involved with its average molecular weight. Both the average molecular weight and the exact distribution of different molecular weights within a polymer are required in order to fully characterize it. The control of molecular weight and molecular weight distribution (MWD) is often used to obtain and improve certain desired physical properties in a polymer product.
当人们谈到聚合物分子量的时候，他所指的是和(适用于)低分子化合物的分子量完全不同的另一回事。聚合物与小分子量化合物的不同在于聚合物的分子量是多分散性的或不均匀的。即使聚合物在没有污物和杂质的情况下被合成，在人们广泛接受的意义上，它仍然不是纯物质。最纯净的聚合物是具有不同分子量的分子的混合物。聚合物多分散性在于聚合过程中展现的统计变化。当我们讨论聚合物的分子量，准确的含义是平均分子量。为了充分地表征聚合物，不仅要求平均分子量，而且也要求聚合物内不同分子量的确切的分布情况。为了获得和改善聚合物产品的某些理想的物理性质，我们经常需要控制分子量和分子量分布。
Various methods are available for the experimental measurement of the average molecular weight of a polymer sample. These include methods based on colligative properties, light scattering, viscosity, ultracentrifugation, and sedimentation. The various methods do not yield the same average molecular weight. Different average molecular weights are obtained because the properties being measured are biased different toward the different sized polymer molecules in a polymer sample. Some methods are biased toward the larger sized polymer molecules, while other methods are biased toward the smaller sized molecules. The result is that the average molecular weights obtained are correspondingly biased toward the larger or smaller sized molecules. The most important average
molecular weights which are determined are the number-average molecular weight Mn, the weight-average molecular weight Mw and the viscosity-average molecular weight Mv.
在聚合物样品平均分子量的实验测试中有许多方法可以利用。这些方法基于依数性，光散射，粘度法，超速离心分离，沉降法。不同的方法得到不同的平均分子量。(对同一聚合物)得到了不同的平均分子量，因为所测得的性质对试样中不同尺寸的聚合物分子有不同的偏差。一些方法对较大尺寸的聚合物分子有偏差（倾向性），而另外一些方法则对较小尺寸的聚合物分子有偏差（倾向性）。所获得的平均分子量分别对较大的或较小的分子有（偏差）倾向性。被测定的最重要平均分子量有数均分子量Mn, 重均分子量Mw,和粘均分子量Mv.
In addition to the different average molecular weights of a polymer sample, it is frequently desirable and necessary to know the exact distribution of molecular weights. A variety of different fractionation methods are used to determine the molecular weight distribution of a polymer sample. These are based on fractionation of a polymer sample using properties, such as solubility and permeability, which vary with molecular weight.
除聚合物样品的不同的平均分子量外，经常需要知道确切的分子量分布。各种各样的不同的分级方法被用来确定聚合物样品的分子量分布。这些方法基于使用诸如溶解性，渗透性等性质进行聚合物样品的分级，这些性质随着分子量变化而变化。
UNIT 7 Polymer Solution 第七单元 聚合物溶液
Dissolving a polymer is a slow process that occurs in two stages. First, solvent molecules slowly diffuse into the polymer to produce a swollen gel. This may be all that happens if，for example，the