聚合物合金为什么要结晶

㈠ 为什么一般情况下缩聚物都能结晶

影响高分子结晶的因素及其表征

在诸多影响高分子聚合物结晶能力的因素中，既有外界温度、
时间与作用力等条件，
又有高分子聚合物本身结构的因素。
由于分子
结构的不同，
有能够结晶和不能结晶之分，
也有易于结晶和难以结晶
之分，还有熔点高低之分。

（
1
）化学结构的影响

从分子结构来看，线型高分子聚合物、
支链型高分子聚合物和交联度不大的网状结构高分子聚合物都能够
进行结晶。而体型结构的高分子聚合物，如酚醛树脂、硬质橡胶等，
就根本不可能产生结晶。

大多数橡胶，如天然橡胶、聚异戊二烯橡胶、顺丁橡胶、反式聚
丁二烯橡胶和氯丁橡胶等，
在结构上均为有规则的立体构型，
均能结
晶。从高分子聚合物的结构上来看，化学结构越简单，分子链规则的
或者大部分规则的就越容易产生结晶。
用一般工艺合成生产的丁苯橡
胶、丁腈橡胶等，
由于其侧基排列不规则，链节的首尾相接的方式也
无规律可言，
甚至是含有一些支链结构，
更使分子链的结构极不规整，
所以这类橡胶不能进行结晶。使用齐格勒
-
纳塔催化体系而聚合的顺
丁橡胶，由于其结构规整性理想就比较容易结晶。

（
2
）分子间作用力的影响

分子间的作用力有利于将分子结合
在晶体之中，从而提高了结晶的能力。

有强极性基的高分子聚合物，
特别是能形成氢键的聚酰酸
（即尼
龙），它甚至在熔融状态时也能产生半有序区（即结晶中心）。对于
橡胶类来说，以天然橡胶和氯丁橡胶相比较，

后者的分子间作用力
比前者大，所以就易于结晶，熔点也比较高。

但是，
如果高分子聚合物的极性太大，
以致使分子链段不能有任
何运动的可能性时（如纤维素），虽然其分子链本身较为规整，也不
能进行结晶，这也是其柔性因素所影响的结果。

（
3
）
分子链柔性的影响

对于柔性分子链的高分子聚合物来说，
柔性过小则不易转变为有序排列，也就不易结晶。

总而言之，高分子聚合物的分子结构对结晶的影响是比较复杂
的，即使是结构非常类似的同类高聚物，如天然橡胶和顺式
-1
，
4-
聚异戊二烯橡胶，它们冷冻结晶的速度和伸长结晶的速度都不一样。
这可能是由于天然橡胶微观结构比较整齐，相对分子质量也比较大，
有极性组分和有一部分天然杂质，
致使冷冻结晶速度较快，
其熔点也
较高。
一般天然橡胶和顺丁橡胶在低温下可以结晶，
橡胶一旦结晶就
会失去弹性，变得跟塑料一样。拉伸模量、剪切模量等性能剧增，延
伸率、回弹性骤减。

高分子的结构规整度对其能否结晶看两个方面：内部因素，外
部条件

内部因素中，
立构规整度只是有利于结晶，
但并不是唯一的决定
因素。
如侧基很大，
严重影响了其结晶的能力，
根本就不能排入晶格，
那就自然不能结晶了。
或者这个链根本就是刚性的，
那即使是规整的
对其结晶也是无用的。

外部因素：有些结晶速度很快的，迅速冻结，根本来不及结晶，
那它自然不能结晶。

总之，不是什么高分子都能结晶的，要链段比较规整，如长的
烷基链比较好结晶，
但都是相对来说，
且结晶条件一般来讲相当苛刻，
很多都是要在高温下，高压下或是在高温下缓慢降温才能得到晶体，
且结晶时间一般都要很长，
缺陷也很大，
当然在极端条件下形成结晶
较完好的结晶聚合物它的力学性能是非常好的！
还有如果高分子长链
结构比较复杂，
但中间有部分是比较规整的链段那么在结晶的时候高
分子会部分结晶，
也就是说无序的结构比较复杂的那部分链段还是无
法结晶，但规整那部分可以结晶，会形成部分的物理交联，这样形成
的部分结晶聚合物的强度等方面的性能会提高。
比如串晶一类的，
力
学性能也比较好。

㈡ 聚合物结晶过程有什么特点

特点：对称性，越高越易结晶 。规整性：对于主链中含有手性中心的聚合物，如果手性中心的构型完全是无规的，使高分子链的对称性和规则性都遭到破坏，这样的高分子一般不能结晶。

如果两种共聚单元的共聚物有相同类型的结晶结构，那么共聚物也能结晶，分子间力也往往使链柔顺性降低，影响结晶能力，分子间能形成氢键，则利于结晶结构的稳定。

聚合物结晶出现边熔融边升温的现象是由于其含有一系列不同完善程度的晶体所致。因为，聚合物在结晶过程中，一些分子链未经充分调整以最稳定的状态排入晶胞就被固定在晶格中，使得结晶中含有不同完善程度的结晶。

结晶的完善程度愈低，其稳定性愈差，熔融温度就愈低，随着结晶完善程度的提高，熔融温度逐渐升高，最后熔融的是完善程度最高即热力学上最稳定的结晶，所以，在一般的升温速度下观察到聚合物结晶在熔融过程中是边熔融边升温，有较宽的熔限。

其他：

影响因素：

1、拉伸：拉伸使聚合物结晶前分子链取向，分子无序程度降低，这样，熔融前后聚合物晶态与非晶态之间转变的熵变∣ΔSm∣减少，结果可提高聚合物结晶能力（可使结晶过程ΔG减小）和结晶度以及提高聚合物结晶的熔点。

2、晶片厚度：聚合物片晶是由折叠链组成的，晶片表面的分子链折叠部分是不规则的，晶片内部分子链是有序排列的，晶片的厚度增加意味着晶体的完善性增加，则晶体的熔点将提高。

3、分子链结构：分子链的柔顺性影响着结晶聚合物的熔融熵ΔSm，分子链柔顺性越大，则结晶聚合物的熔融熵ΔSm越大。而分子间作用力变化影响着结晶聚合物的熔融热ΔHm。

通常，分子间作用力变化越大，则结晶聚合物的ΔHm越大。

以上内容参考：结晶聚合物-网络

㈢ 聚合物结晶对性能会产生哪些影响

结晶可以使聚合物强度硬度增加，但结晶后分子链和链段规整排列到晶格中，运动困难，会使韧性下降易发生脆性断裂。同时由于晶区和非晶区的折射率不同，聚合物会变的不透明。

㈣ 什么是聚合物的结晶

聚合物是通称一些非常长的分子，当中由结构单位和重覆单位经共价化学键连接一起。 (英文Polymer起源自希腊语中polys即"许多"，meros即部分)。 聚合物与其它分子不同之处在於他们是由许多相同、相似或互补的亚单位重复所组成。这些亚单位或称单体是一些低至中等分子质量的分子，他们经聚合作用的化学反应便可组成聚合物。

相似的单体由於有不同的取代基，所以不会是完全相同的。由不同的单体组成的聚合物会有不同的特性例如：溶解度、弹性和强度。譬如在蛋白质里、这些差异使聚合物能形成其独特的生物活跃构象(参见自我组装)。当中相同单体如有非活泼的支链会导致聚合物链形成一无规线团——即根据数学模型所描述的理想链。虽然多数聚合物是有机化合物，并由碳基之单体所组成，但是也有无机聚合物例如，矽橡胶(又称硅树脂)是由交替的硅和氧原子所组成。

目录 [隐藏]
1 Polymer nomenclature
2 聚合物的物理性质
2.1 Branching
2.2 Stereoregularity
3 Constitution of polymers
3.1 Copolymers
4 Chemical properties of polymers
4.1 Intermolecular forces
4.2 Polymer characterization
5 See also
6 External links

[编辑]
Polymer nomenclature
Polymers are typically classified according to three main groups:

thermoplastics (linear or branched chains)
thermosets (crosslinked chains)
elastomers
Coordination polymers
The term polymer covers a large, diverse group of molecules, including substances from proteins to stiff, high-strength Kevlar fibres. For example, the formation of polyethene (also called polyethylene) involves thousands of ethene molecules bonded together to form a straight (or branched) chain of repeating -CH2-CH2- units (with a -CH3 at each terminal):

Polymers are often named in terms of the monomer from which they are made. Because it is synthesized from ethene in a process ring which all the double bonds in the vinyl monomers are lost, polyethene has the unsaturated structure:

If it were named according to its final structure, it would have the alkane designation "polyethane".

Because synthetic polymer formation is governed by random assembly from the constituent monomers, polymer chains within a solution or substance are generally not of equal length. This is unlike basic, smaller molecules in which every atom is stoichiometrically accounted for, and each molecule has a set molecular mass. An ensemble of differing chain lengths, often obeying a normal (Gaussian) distribution, occurs because polymer chains terminate ring polymerization after random amounts of chain lengthening (propagation).

Proteins are polymers of amino acids. Typically, hundreds of the (nominally) twenty different amino acid monomers make up a protein chain, and the sequence of monomers determines its shape and biological function. (There are also shorter oligopeptides which function as hormones.) But there are active regions, surrounded by, as is believed now (Aug 2003), structural regions, whose sole role is to expose the active regions. (There may be more than one on a given protein.) So the exact sequence of amino acids in certain parts of the chains can vary from species to species, and even given mutations within a species, so long as the active sites are properly accessible. Also, whereas the formation of polyethylene occurs spontaneously under the right conditions, the synthesis of biopolymers such as proteins and nucleic acids requires the help of enzyme catalysts, substances that facilitate and accelerate reactions. Unlike synthetic polymers, these biopolymers have exact sequences and lengths. (This does not include the carbohydrates.) Since the 1950s, catalysts have also revolutionised the development of synthetic polymers. By allowing more careful control over polymerization reactions, polymers with new properties, such as the ability to emit coloured light, have been manufactured.

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聚合物的物理性质
聚合物的物理性质包括聚合度，分子量分布，结晶度和相转变等，详见高分子物理学。

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Branching
See also: Branching (chemistry)

During the propagation of polymer chains, branching can occur. In free-radical polymerization, this occurs when a chain curls back and bonds to an earlier part of the chain. When this curl breaks, it leaves small chains sprouting from the main carbon backbone. Branched carbon chains cannot line up as close to each other as unbranched chains can. This causes less contact between atoms of different chains, and fewer opportunities for inced or permanent dipoles to occur. A low density results from the chains being further apart. Lower melting points and tensile strengths are evident, because the intermolecular bonds are weaker and require less energy to break.

Besides branching, polymers can have other topologies: linear, network (cross-linked 3D structure), IPN (integrated polymer network), comb, or star as well as dendrimer and hyperbranched structures.

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Stereoregularity
Stereoregularity or tacticity describes the isomeric arrangement of functional groups on the backbone of carbon chains. Isotactic chains are defined as having substituent groups aligned in one direction. This enables them to line up close to each other, creating crystalline areas and resulting in highly rigid polymers.

In contrast, atactic chains have randomly aligned substituent groups. The chains do not fit together well and the intermolecular forces are low. This leads to a low density and tensile strength, but a high degree of flexibility.

Syndiotactic substituent groups alternate regularly in opposite directions. Because of this regularity, syndiotactic chains can position themselves close to each other, though not as close as isotactic polymers. Syndiotactic polymers have better impact strength than isotactic polymers because of the higher flexibility resulting from their weaker intermolecular forces.

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Constitution of polymers
[编辑]
Copolymers
Copolymerization with two or more different monomers results in chains with varied properties. There are twenty amino acid monomers whose sequence results in different shapes and functions of protein chains. Copolymerising ethene with small amounts of 1-hexene (or 4-methyl-1-pentene) is one way to form linear low-density polyethene (LLDPE). (See polyethylene.) The C4 branches resulting from the hexene lower the density and prevent large crystalline regions from forming within the polymer, as they do in HDPE. This means that LLDPE can withstand strong tearing forces while maintaining flexibility.

A block copolymer is formed when the reaction is carried out in a stepwise manner, leading to a structure with long sequences or blocks of one monomer alternating with long sequences of the other. There are also graft copolymers, in which entire chains of one kind (e.g., polystyrene) are made to grow out of the sides of chains of another kind (e.g., polybutadiene), resulting in a proct that is less brittle and more impact-resistant. Thus, block and graft copolymers can combine the useful properties of both constituents and often behave as quasi-two-phase systems.

The following is an example of step-growth polymerization, or condensation polymerization, in which a molecule of water is given off and nylon is formed. The properties of the nylon are determined by the R and R' groups in the monomers used.

Image:Con polymer.png
The first commercially successful, completely synthetic polymer was nylon 6,6, with alkane chains R = 4C (adipic acid) and R' = 6C (hexamethylene diamine). Including the two carboxyl carbons, each monomer donates 6 carbons; hence the name. In naming nylons, the number of carbons from the diamine is given first and the number from the diacid second. Kevlar is an aromatic nylon in which both R and R' are benzene rings.

Copolymers illustrate the point that the repeating unit in a polymer, such as a nylon, polyester or polyurethane, is often made up of two (or more) monomers.

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Chemical properties of polymers
[编辑]
Intermolecular forces
The attractive forces between polymer chains play a large part in determining a polymer's properties. Because polymer chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules. Also, longer chains are more amorphous (randomly oriented). Polymers can be visualised as tangled spaghetti chains - pulling any one spaghetti strand out is a lot harder the more tangled the chains are. These stronger forces typically result in high tensile strength and melting points.

The intermolecular forces in polymers are determined by dipoles in the monomer units. Polymers containing amide groups can form hydrogen bonds between adjacent chains; the positive hydrogen atoms in N-H groups of one chain are strongly attracted to the oxygen atoms in C=O groups on another. These strong hydrogen bonds result in, for example, the high tensile strength and melting point of kevlar. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so ethene's melting point and strength are lower than Kevlar's, but polyesters have greater flexibility.

Ethene, however, has no permanent dipole. The attractive forces between polyethene chains arise from weak van der Waals forces. Molecules can be thought of as being surrounded by a cloud of negative electrons. As two polymer chains approach, their electron clouds repel one another. This has the effect of lowering the electron density on one side of a polymer chain, creating a slight positive dipole on this side. This charge is enough to actually attract the second polymer chain. Van der Waals forces are quite weak, however, so polyethene melts at low temperatures.

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Polymer characterization
The characterization of a polymer requires several parameters which need to be specified. This is because a polymer actually consists of a statistical distribution of chains of varying lengths, and each chain consists of monomer resies which affect its properties.

A variety of lab techniques are used to determine the properties of polymers. Techniques such as wide angle X-ray scattering, small angle X-ray scattering, and small angle neutron scattering are used to determine the crystalline structure of polymers. Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, and polydispersity. FTIR is used to determine composition. Thermal properties such as the glass transition temperature and melting point can be determined by differential scanning calorimetry and dynamic mechanical analysis. Pyrolysis followed by analysis of the fragments is one more technique for determining the possible structure of the polymer.

Polymer known as polymer substrate is used for everyday banknotes in Australia, Romania, Papua New Guinea, Samoa, Zambia, Vietnam, New Zealand and a few others, and the material is also used in commemorative notes in some other countries. The process of polymer substrate creation was developed by the Australia CSIRO.

㈤ 为什么聚合物的结晶度是决定制品性能的重要因素之一

对于吹塑成型，结晶一方面是有利的，因为结晶可被冻结在拉伸取向中，使取向结构具有稳定性;结晶可提高制品的许多重要性能，如密度、刚度、硬度、拉伸强度、耐化学剂性和阻渗透性。但另一方面，结晶会降低制品的一些使用性能，如极限伸长、耐冲击韧性、透明度和耐环境应力开裂性。当这些性能要求高时，一般采用共聚以降低分子规整性与结晶或通过适当的冷却速率来满足性能要求。由于聚合物的导热性能较差，把温度较高的型坯吹胀后使之贴紧温度较低的模具型腔时，会形成较大的温度梯度，制品的表层会快速冷却，产生较低的结晶度，而内部冷却较慢，结晶度高。

㈥ 聚合物的结晶特点

固体聚合物可划分为结晶态聚合物和非晶态聚合物，其中非晶态聚合物又称为无定形聚合物。结晶态聚合物是指，在高聚物微观结构中存在一些具有稳定规整排列的分子的区域，这些分子有规则紧密排列的区域称为结晶区。存在结晶区的高聚物称为结晶态高聚物。
一般来说，高聚物的结晶总是从非晶态熔体中形成的，结晶态高聚物中实际上仍包含着非晶区，其结晶的程度可用结晶度来衡量。结晶度是指聚合物中的结晶区在聚合物中所占的重量百分数。通常，分子结构简单、对称性高的聚合物以及分子间作用力较大的聚合物等从高温向低温转变时都能结晶。例如聚乙烯(pe）的分子结构简单，对称性好，故当温度由高到低转变时易发生结晶。又如聚酰胺的分子链虽比较长，但由于其分子结构中“酰胺”的存在，使得分子之间容
易形成氢键，增大了分子间的作用力，因此当温度由高到低转变时也容易出现结晶现象。高聚物的结晶与低分子结晶区别很大，晶态高聚物的晶体结晶不完全，而且晶体也不及小分子晶体整齐，结晶速度慢，且没有明显的熔点，而是一个熔融的温度范围，通常称为熔限。聚合物的结晶有很多不同的形态，但以球晶形态居多。聚合物一旦发生结晶，则其性能也将随之产生相应变化。结晶可导致聚合物的密度增加，这是因为结晶使得聚合物本体的微观结构变得规整而紧密的缘故。这种由结晶而导致的规整而紧密的微观结构还可使聚合物的拉伸强度增大，冲击强度降低，弹性模量变小，同时，结晶还有助于提高聚合物的软化温度和热变形温度，使成型的塑件脆性加大，表面粗糙度值增大，而且还会导致塑件的透明度降低甚至丧失。
注射成型后的塑件是否会产生结晶以及结晶度的大小都与成型过程中塑件的冷却速率有很大关系。由于结晶度对塑件的性能有很大影响，工业上常采用热处理方式来提高塑件的性能。

㈦ 什么是聚合物的结晶和取向研究结晶和取向对高分子成型加工有何实际意义

这个问题可以写一本书。简单的说一下吧：
某些聚合物的分子链结构比较规整或含有大量能够相互形成氢键的基团，熔体冷却时，聚合物分子链规则地排列（同时或有氢键参与），其结果是产生结晶。常见的非极性结晶/半结晶聚合物有聚丙烯、聚乙烯等。常见的极性结晶聚合物有尼龙、聚酯等。
聚合物的结晶有利有弊，好处在于，结晶可以提高制品的刚度和拉伸、弯曲等机械强度；坏处在于结晶过程通常导致聚合物不透明、冲击强度受到影响、结晶过程导致相对较大的成型收缩率，容易导致翘曲变形等。
取向是指聚合物熔融加工过程中，长链状分子在剪切力作用下沿着熔体流动方向排列，并在冷却固化过程中被固定下来的现象。其负面影响主要是导致流动方向和垂直方向不均一的内应力和收缩率，使得制品尺寸及外形受到影响，并可能导致机械性能的不均一。取向的好处是，在某些应用中，取向方向的机械强度较大。

㈧ 影响聚合物结晶的因素

影响聚合物结晶的因素可以分两部分：内部结构的规整性、外部的浓度、溶剂、温度等。结构越规整，越容易结晶，反之则越不容易，成为无定型聚合物。与无机物和小分子有机物相比，没有完全结晶的聚合物。这是最主要的因素了。

㈨ 影响聚合物结晶的因素

影响聚合物结晶的内在因素

1、高分子链的对称性：对称性好，容易结晶。例如：PTFE和PE对称性好，容易结晶，其中PE最高结晶度高达95%，当PE氯化后，破坏对称性，结晶能力大大降低。

2、高分子链的规整性：一般考虑含有不对称中心的高分子或者具有顺反异够的高分子，规整性好，容易结晶。

3、分子间作用力：分子间能形成氢键时，有利于稳定结晶结构。

例如：PVA为非结晶性聚合物，但是水解后，得到的聚乙烯醇却能结晶，这是因为氢键的作用。

(9)聚合物合金为什么要结晶扩展阅读

聚合物在不同条件下结晶时，可能得到的结晶形态：单晶、树枝晶、球晶、纤维状晶、串晶、柱晶、伸直链晶体。形态特征为：

（1）单晶：分子链垂直于片晶平面排列，晶片厚度一般只有10nm左右；

（2）树枝晶：许多单晶片在特定方向上的择优生长与堆积形成树枝状；

（3）球晶：呈圆球状，在正交偏光显微镜下呈现特有的黑十字消光，有些出现同心环；

（4）纤维状晶：晶体呈纤维状，长度大大超过高分子链的长度；

（5）串晶：在电子显微镜下，串晶形如串珠；

（6）柱晶：中心贯穿有伸直链晶体的扁球晶，呈柱状；

（7）伸直链晶体：高分子链伸展排列晶片厚度与分子链长度相当。