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。 The control of molecular weight is essential for the practical application of a polymerization process.
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.
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。
Polymers differ from the small-sized compounds in that they are polydisperse or heterogeneous in molecular weight.
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。 Even if a polymer is synthesized free from contaminants and impurities, it is still not a pure substance in the usually accepted sense.
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。
Polymers, in their purest form, are mixture of molecules of different molecular weights.
最纯净的聚合物是具有不同分子量的分子的混合物。
The reason for the polydispersity of polymers lies in the statistical variations present in the polymerization processes.
聚合物多分散性在于聚合过程中展现的统计变化。
When one discusses the molecular weight of a polymer, one is actually involved with its average molecular weight.
当我们讨论聚合物的分子量，准确的含义是平均分子量。
Both the average molecular weight and the exact distribution of different molecular weights within a polymer are required in order to fully characterize it.
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。
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. 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.
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。
These include methods based on colligative properties, light scattering, viscosity, ultracentrifugation, and sedimentation.
这些方法基于依数性，光散射，粘度法，超速离心分离，沉降法。 The various methods do not yield the same average molecular weight. 不同的方法得到不同的平均分子量。
Different average molecular weights are obtained because the properties being measured are biased different toward the different sized polymer molecules in a polymer
sample.
(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。
Some methods are biased toward the larger sized polymer molecules, while other methods are biased toward the smaller sized molecules. 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）。
The result is that the average molecular weights obtained are correspondingly biased toward the larger or smaller sized molecules.
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。
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.。
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. 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。
A variety of different fractionation methods are used to determine the molecular weight distribution of a polymer sample.
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。
These are based on fractionation of a polymer sample using properties, such as solubility and permeability, which vary with molecular weight.
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
Dissolving a polymer is a slow process that occurs in two stages. 溶解高分子需要一个缓慢的过程，这个过程分两步发生。
First, solvent molecules slowly diffuse into the polymer to produce a swollen gel. 溶剂分子缓慢地扩散到高分子中产生溶胀凝胶。
This may be all that happens if，for example，the polymer-polymer intermolecular forces are high because of crosslinking，crystallinity·or strong hydrogen bonding. 例如, 如果因交联，结晶和很强的氢键而形成很大的分子间力，(聚合物的溶解过程)有可能就只停留在这一阶段。
But if these forces can be overcome by the introduction of strong polymer-solvent interactions, the second stage of solution can take place.
但是如果这些力被强的高分子-溶剂之间相互作用克服，溶解的第二阶段就会发生。 Here the gel gradually disintegrates into a true solution. 即，凝胶逐渐变成一个真正的溶液。
Only this stage can be materially speeded by agitation. 只有这个阶段可以通过搅拌得到明显促进。
Even so, the solution process can be quite slow (days or weeks) for materials of very
high molecular weight.
虽然如此，对高分子量的材料而言，溶解过程是相当缓慢的（几天或几个星期）。 Solubility relations in polymer systems are more complex than those among low molecular-weight compounds, because of the size differences between polymer and solvent molecules, the viscosity of the system, and the effects of the texture and molecular weight of the polymer.
因为高分子和溶剂分子之间尺寸上的区别，体系的粘度以及聚合物分子量及织态结构的影响等原因，高分子体系的溶解性关系比低分子量化合物要复杂得多。
In turn，the presence or absence of solubility as conditions(such as the nature of the solvent，or the temperature)are varied can give much information about the polymer. 当条件(溶剂的性质或温度)变化的时候，有无溶解性又可提供出许多关于这种聚合物的信息。
As specified in the literature，the arrangements of the polymer chain differing by reason of rotations about single bands are termed conformations. 正如在文献中所定义的那样，由于围绕着单键的旋转而导致的聚合物链不同的空间排布叫做构象。
In solution, a polymer molecule is a randomly coiling mass most of whose conformations occupy*‘okjupai+ many times the volume of its segments alone.
在溶液中，聚合物分子是无规线团状,而大部分构象占链段分子自身体积的许多倍。 The average density of segments within a dissolved polymer molecule is of 10-4~10-5g/cm3.
溶解聚合物分子里的平均链段密度是10-4~10-5g/cm3
The size of the molecular coil is very much influenced by the polymer-solvent interaction forces.
聚合物-溶剂之间的作用力对分子线团尺寸有很大的影响。
In a thermodynamically “good” solvent, where polymer-solvent contacts are highly favored, the coils are relatively extended.
在热力学上的好溶剂中，聚合物-溶剂作用较强，线团是相对伸展的。 In a “poor” solvent they are relatively contracted. 而在不良溶剂中，线团则是相对收缩的。
It is the purpose to describe the conformational properties of both ideal and real polymer chains.
使用上述方法的目的是描述理想的和真实的聚合物链构象。
The importance of the random-coil nature of the dissolved, molten, amorphous, and glassy states of high polymers cannot be overemphasized.
我们无论怎样强调溶解的，熔融的，无定形的，玻璃态的高分子无规线团性质的重要性都不过分。
Many important physical as well as thermodynamic properties of high polymers result from this characteristic structural feature.
高分子的许多重要的物理及热力学性质都是这个结构特征引起的。
The random coil(Fig. 7. 1) arises from the relative freedom of rotation associated with the chain bonds of most polymers and the formidably large number of conformations accessible to the molecule.
无规线团(图7. 1)一方面是由于聚合物链上的键自由旋转而产生的，另一方面是由于(聚合物)分子 (链)可达到巨大的构象数而产生的。Fig. Tab.
One of these conformations, the fully extended chain has special interest because its length, the contour length of the chain, can be calculated in a straightforward way.
我们对这些构象之一，也是充分伸展的链有特殊的兴趣，因为它的长度，即链的伸直长度可以直接地计算出来。
In all other cases the size of the random coil must be expressed in terms of statistical parameters such as the root-mean-square distance between its ends, (r2)1/2, or its radius of gyration, the root-mean-square distance of the elements of the chain from its center of gravity, (s2)1/2.
在所有其他的场合，无规线团的尺寸必须用统计参数来表示，如链末端之间距离的均方根，(r2)1/2或回旋半径，从分子重心（质心）到链节距离的均方根(s2)1/2
For linear polymers that are not appreciably extended beyond their most probable shape, the mean-square end-to-end distance and the square of the radius of gyration are simply related:r2=6s2. For extended chains r2>6s2.
在线型聚合物的形状没有超出的充分伸展的情况下，平均末端距离的平方和回转半径之间可以简单地相关：r2=6s2。对伸展链则有：r2>6s2.
The use of the radius of gyration is sometimes preferred because it can be determined experimentally.
有时回旋半径更为常用，因为它可以用实验来确定。
UNIT 8 Morphology of Solid Polymers
Solid polymers differ from ordinary, low molecular weight compounds in the nature of their physical state or morphology.
固体聚合物在物理态的性质或形态是有别于普通低分子量化合物。
Most polymers simultaneously show the characteristics of both crystalline solids and highly viscous liquids.
大多数聚合物同时体现结晶固体和高粘液体的特性。
X-ray and electron diffraction patterns often show the sharp features typical of three-dimensionally ordered，crystalline materials as well as the diffuse features materials characteristic of liquids.
(固体聚合物的)X射线图样和电子衍射图样常常会显示出三维有序晶体材料所具有的边缘清晰的特征，也会显示出液体的所具有的边缘模糊的特征。
The fringed-micelle theory, developed in the 1930’s, considers polymer to consist of small-sized, ordered crystalline regions-termed crystallities-imbedded in an unordered, amorphous polymer matrix.
在上世纪三十年代发展的缨状胶束理论认为聚合物由小尺寸，规则晶区即所谓的微晶包埋到不规则的，无定形聚合物基体组成。
Polymer molecules are considered to pass through several different crystalline regions with crystallites being formed when segments from different polymer chains are precisely aligned together and undergo crystallization.
当来自不同聚合物链的链段精确地排列在一起结晶时， 认为伴随着微晶的生成，
聚合物分子会通过几个不同的晶区.
Each polymer chain can contribute ordered segments to several crystallities. 每个聚合物链可以提供规则链段到几个微晶。
The segments of the chain in between the crystallites make up the unordered amorphous matrix. This concept of polymer crystallinity is shown in Fig. 7.1.
在微晶之间的聚合物链段形成不规则的无定形基体。聚合物结晶性概念如图7.1所示。
The folded-chain lamella theory arose in the late 1950’s when polymer single crystals in the form of thin platelets termed lamella were grown form polymer solutions.
上世纪50年代末期，当（发现）聚合物单晶以薄片的形式即所谓的片晶从聚合物溶液中生长的时候，提出了折叠链片晶理论。
The diffraction patterns of these single crystals indicate that the polymer molecules fold back and forth on themselves like in an accordion in the process of crystallization (Fig. 7.2).
这些单晶的衍射图显示，在结晶过程中，聚合物分子来回折叠就像一个手风琴。 The theory of chain-folding applies generally to most polymers-not only for solution-grown single crystals, but also for polymers crystallized from the melt.
折叠理论一般应用于大多数高分子，不仅用于溶液生长单晶，而且也适用于熔融结晶聚合物。
Semi-crystalline polymers are considered by advocates of the folded-chain theory to be chain-folded crystal with varying amounts of defects.
折叠链理论的拥护者认为半结晶聚合物是具有不同数量缺陷的折叠链晶体。
The crystallinity of polymers is pictured as being completely similar to that of low molecular weight compounds.
聚合物的结晶性可想象成完全类似于低分子量化合物的结晶性。
The defects in the chain folded crystals may be imperfect folds, irregularities in packing, chain entanglements, loose chain ends, dislocations, occluded impurities, or numerous other imperfections.
在链折叠结晶中的缺陷可以是不完整的折叠，不规则的堆砌，链缠结，疏松的链末端，错位，夹杂的杂质或许多其他的不完整性。
The fringed-micelle and folded-chain theories of polymer crystallinity are often considered to be mutually exclusive but they need not be so considered.
经常认为聚合物结晶的缨状胶束和折叠链理论是相互排斥的，其实不是这样的。 It is usually practical to adopt a working model of polymer crystallinity which employs the features of both concepts.
实际工作中常采用聚合物结晶性的工作模型，这个模型兼有两者的特征。
The folded chain theory is especially well suited for highly crystalline polymers where one can consider them to be one phase crystalline systems with defects. 折叠链理论特别适用于高结晶聚合物，高结晶聚合物被认为是具有缺陷的单相结晶体系。
Polymers with medium to low crystallinity can often be advantageously treated by the fringed micellel concept as two phase systems composed of crystallites imbedded in uncrystallized，amorphous polymer.