聚合物合金為什麼要結晶

㈠ 為什麼一般情況下縮聚物都能結晶

影響高分子結晶的因素及其表徵

在諸多影響高分子聚合物結晶能力的因素中，既有外界溫度、
時間與作用力等條件，
又有高分子聚合物本身結構的因素。
由於分子
結構的不同，
有能夠結晶和不能結晶之分，
也有易於結晶和難以結晶
之分，還有熔點高低之分。

（
1
）化學結構的影響

從分子結構來看，線型高分子聚合物、
支鏈型高分子聚合物和交聯度不大的網狀結構高分子聚合物都能夠
進行結晶。而體型結構的高分子聚合物，如酚醛樹脂、硬質橡膠等，
就根本不可能產生結晶。

大多數橡膠，如天然橡膠、聚異戊二烯橡膠、順丁橡膠、反式聚
丁二烯橡膠和氯丁橡膠等，
在結構上均為有規則的立體構型，
均能結
晶。從高分子聚合物的結構上來看，化學結構越簡單，分子鏈規則的
或者大部分規則的就越容易產生結晶。
用一般工藝合成生產的丁苯橡
膠、丁腈橡膠等，
由於其側基排列不規則，鏈節的首尾相接的方式也
無規律可言，
甚至是含有一些支鏈結構，
更使分子鏈的結構極不規整，
所以這類橡膠不能進行結晶。使用齊格勒
-
納塔催化體系而聚合的順
丁橡膠，由於其結構規整性理想就比較容易結晶。

（
2
）分子間作用力的影響

分子間的作用力有利於將分子結合
在晶體之中，從而提高了結晶的能力。

有強極性基的高分子聚合物，
特別是能形成氫鍵的聚醯酸
（即尼
龍），它甚至在熔融狀態時也能產生半有序區（即結晶中心）。對於
橡膠類來說，以天然橡膠和氯丁橡膠相比較，

後者的分子間作用力
比前者大，所以就易於結晶，熔點也比較高。

但是，
如果高分子聚合物的極性太大，
以致使分子鏈段不能有任
何運動的可能性時（如纖維素），雖然其分子鏈本身較為規整，也不
能進行結晶，這也是其柔性因素所影響的結果。

（
3
）
分子鏈柔性的影響

對於柔性分子鏈的高分子聚合物來說，
柔性過小則不易轉變為有序排列，也就不易結晶。

總而言之，高分子聚合物的分子結構對結晶的影響是比較復雜
的，即使是結構非常類似的同類高聚物，如天然橡膠和順式
-1
，
4-
聚異戊二烯橡膠，它們冷凍結晶的速度和伸長結晶的速度都不一樣。
這可能是由於天然橡膠微觀結構比較整齊，相對分子質量也比較大，
有極性組分和有一部分天然雜質，
致使冷凍結晶速度較快，
其熔點也
較高。
一般天然橡膠和順丁橡膠在低溫下可以結晶，
橡膠一旦結晶就
會失去彈性，變得跟塑料一樣。拉伸模量、剪切模量等性能劇增，延
伸率、回彈性驟減。

高分子的結構規整度對其能否結晶看兩個方面：內部因素，外
部條件

內部因素中，
立構規整度只是有利於結晶，
但並不是唯一的決定
因素。
如側基很大，
嚴重影響了其結晶的能力，
根本就不能排入晶格，
那就自然不能結晶了。
或者這個鏈根本就是剛性的，
那即使是規整的
對其結晶也是無用的。

外部因素：有些結晶速度很快的，迅速凍結，根本來不及結晶，
那它自然不能結晶。

總之，不是什麼高分子都能結晶的，要鏈段比較規整，如長的
烷基鏈比較好結晶，
但都是相對來說，
且結晶條件一般來講相當苛刻，
很多都是要在高溫下，高壓下或是在高溫下緩慢降溫才能得到晶體，
且結晶時間一般都要很長，
缺陷也很大，
當然在極端條件下形成結晶
較完好的結晶聚合物它的力學性能是非常好的！
還有如果高分子長鏈
結構比較復雜，
但中間有部分是比較規整的鏈段那麼在結晶的時候高
分子會部分結晶，
也就是說無序的結構比較復雜的那部分鏈段還是無
法結晶，但規整那部分可以結晶，會形成部分的物理交聯，這樣形成
的部分結晶聚合物的強度等方面的性能會提高。
比如串晶一類的，
力
學性能也比較好。

㈡ 聚合物結晶過程有什麼特點

特點：對稱性，越高越易結晶 。規整性：對於主鏈中含有手性中心的聚合物，如果手性中心的構型完全是無規的，使高分子鏈的對稱性和規則性都遭到破壞，這樣的高分子一般不能結晶。

如果兩種共聚單元的共聚物有相同類型的結晶結構，那麼共聚物也能結晶，分子間力也往往使鏈柔順性降低，影響結晶能力，分子間能形成氫鍵，則利於結晶結構的穩定。

聚合物結晶出現邊熔融邊升溫的現象是由於其含有一系列不同完善程度的晶體所致。因為，聚合物在結晶過程中，一些分子鏈未經充分調整以最穩定的狀態排入晶胞就被固定在晶格中，使得結晶中含有不同完善程度的結晶。

結晶的完善程度愈低，其穩定性愈差，熔融溫度就愈低，隨著結晶完善程度的提高，熔融溫度逐漸升高，最後熔融的是完善程度最高即熱力學上最穩定的結晶，所以，在一般的升溫速度下觀察到聚合物結晶在熔融過程中是邊熔融邊升溫，有較寬的熔限。

其他：

影響因素：

1、拉伸：拉伸使聚合物結晶前分子鏈取向，分子無序程度降低，這樣，熔融前後聚合物晶態與非晶態之間轉變的熵變∣ΔSm∣減少，結果可提高聚合物結晶能力（可使結晶過程ΔG減小）和結晶度以及提高聚合物結晶的熔點。

2、晶片厚度：聚合物片晶是由折疊鏈組成的，晶片表面的分子鏈折疊部分是不規則的，晶片內部分子鏈是有序排列的，晶片的厚度增加意味著晶體的完善性增加，則晶體的熔點將提高。

3、分子鏈結構：分子鏈的柔順性影響著結晶聚合物的熔融熵ΔSm，分子鏈柔順性越大，則結晶聚合物的熔融熵ΔSm越大。而分子間作用力變化影響著結晶聚合物的熔融熱ΔHm。

通常，分子間作用力變化越大，則結晶聚合物的ΔHm越大。

以上內容參考：結晶聚合物-網路

㈢ 聚合物結晶對性能會產生哪些影響

結晶可以使聚合物強度硬度增加，但結晶後分子鏈和鏈段規整排列到晶格中，運動困難，會使韌性下降易發生脆性斷裂。同時由於晶區和非晶區的折射率不同，聚合物會變的不透明。

㈣ 什麼是聚合物的結晶

聚合物是通稱一些非常長的分子，當中由結構單位和重覆單位經共價化學鍵連接一起。 (英文Polymer起源自希臘語中polys即"許多"，meros即部分)。 聚合物與其它分子不同之處在於他們是由許多相同、相似或互補的亞單位重復所組成。這些亞單位或稱單體是一些低至中等分子質量的分子，他們經聚合作用的化學反應便可組成聚合物。

相似的單體由於有不同的取代基，所以不會是完全相同的。由不同的單體組成的聚合物會有不同的特性例如：溶解度、彈性和強度。譬如在蛋白質里、這些差異使聚合物能形成其獨特的生物活躍構象(參見自我組裝)。當中相同單體如有非活潑的支鏈會導致聚合物鏈形成一無規線團——即根據數學模型所描述的理想鏈。雖然多數聚合物是有機化合物，並由碳基之單體所組成，但是也有無機聚合物例如，矽橡膠(又稱硅樹脂)是由交替的硅和氧原子所組成。

目錄 [隱藏]
1 Polymer nomenclature
2 聚合物的物理性質
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

[編輯]
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.

[編輯]
聚合物的物理性質
聚合物的物理性質包括聚合度，分子量分布，結晶度和相轉變等，詳見高分子物理學。

[編輯]
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.

[編輯]
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.

[編輯]
Constitution of polymers
[編輯]
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.

[編輯]
Chemical properties of polymers
[編輯]
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.

[編輯]
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 為什麼聚合物的結晶度是決定製品性能的重要因素之一

對於吹塑成型，結晶一方面是有利的，因為結晶可被凍結在拉伸取向中，使取向結構具有穩定性;結晶可提高製品的許多重要性能，如密度、剛度、硬度、拉伸強度、耐化學劑性和阻滲透性。但另一方面，結晶會降低製品的一些使用性能，如極限伸長、耐沖擊韌性、透明度和耐環境應力開裂性。當這些性能要求高時，一般採用共聚以降低分子規整性與結晶或通過適當的冷卻速率來滿足性能要求。由於聚合物的導熱性能較差，把溫度較高的型坯吹脹後使之貼緊溫度較低的模具型腔時，會形成較大的溫度梯度，製品的表層會快速冷卻，產生較低的結晶度，而內部冷卻較慢，結晶度高。

㈥ 聚合物的結晶特點

固體聚合物可劃分為結晶態聚合物和非晶態聚合物，其中非晶態聚合物又稱為無定形聚合物。結晶態聚合物是指，在高聚物微觀結構中存在一些具有穩定規整排列的分子的區域，這些分子有規則緊密排列的區域稱為結晶區。存在結晶區的高聚物稱為結晶態高聚物。
一般來說，高聚物的結晶總是從非晶態熔體中形成的，結晶態高聚物中實際上仍包含著非晶區，其結晶的程度可用結晶度來衡量。結晶度是指聚合物中的結晶區在聚合物中所佔的重量百分數。通常，分子結構簡單、對稱性高的聚合物以及分子間作用力較大的聚合物等從高溫向低溫轉變時都能結晶。例如聚乙烯(pe）的分子結構簡單，對稱性好，故當溫度由高到低轉變時易發生結晶。又如聚醯胺的分子鏈雖比較長，但由於其分子結構中「醯胺」的存在，使得分子之間容
易形成氫鍵，增大了分子間的作用力，因此當溫度由高到低轉變時也容易出現結晶現象。高聚物的結晶與低分子結晶區別很大，晶態高聚物的晶體結晶不完全，而且晶體也不及小分子晶體整齊，結晶速度慢，且沒有明顯的熔點，而是一個熔融的溫度范圍，通常稱為熔限。聚合物的結晶有很多不同的形態，但以球晶形態居多。聚合物一旦發生結晶，則其性能也將隨之產生相應變化。結晶可導致聚合物的密度增加，這是因為結晶使得聚合物本體的微觀結構變得規整而緊密的緣故。這種由結晶而導致的規整而緊密的微觀結構還可使聚合物的拉伸強度增大，沖擊強度降低，彈性模量變小，同時，結晶還有助於提高聚合物的軟化溫度和熱變形溫度，使成型的塑件脆性加大，表面粗糙度值增大，而且還會導致塑件的透明度降低甚至喪失。
注射成型後的塑件是否會產生結晶以及結晶度的大小都與成型過程中塑件的冷卻速率有很大關系。由於結晶度對塑件的性能有很大影響，工業上常採用熱處理方式來提高塑件的性能。

㈦ 什麼是聚合物的結晶和取向研究結晶和取向對高分子成型加工有何實際意義

這個問題可以寫一本書。簡單的說一下吧：
某些聚合物的分子鏈結構比較規整或含有大量能夠相互形成氫鍵的基團，熔體冷卻時，聚合物分子鏈規則地排列（同時或有氫鍵參與），其結果是產生結晶。常見的非極性結晶/半結晶聚合物有聚丙烯、聚乙烯等。常見的極性結晶聚合物有尼龍、聚酯等。
聚合物的結晶有利有弊，好處在於，結晶可以提高製品的剛度和拉伸、彎曲等機械強度；壞處在於結晶過程通常導致聚合物不透明、沖擊強度受到影響、結晶過程導致相對較大的成型收縮率，容易導致翹曲變形等。
取向是指聚合物熔融加工過程中，長鏈狀分子在剪切力作用下沿著熔體流動方向排列，並在冷卻固化過程中被固定下來的現象。其負面影響主要是導致流動方向和垂直方向不均一的內應力和收縮率，使得製品尺寸及外形受到影響，並可能導致機械性能的不均一。取向的好處是，在某些應用中，取向方向的機械強度較大。

㈧ 影響聚合物結晶的因素

影響聚合物結晶的因素可以分兩部分：內部結構的規整性、外部的濃度、溶劑、溫度等。結構越規整，越容易結晶，反之則越不容易，成為無定型聚合物。與無機物和小分子有機物相比，沒有完全結晶的聚合物。這是最主要的因素了。

㈨ 影響聚合物結晶的因素

影響聚合物結晶的內在因素

1、高分子鏈的對稱性：對稱性好，容易結晶。例如：PTFE和PE對稱性好，容易結晶，其中PE最高結晶度高達95%，當PE氯化後，破壞對稱性，結晶能力大大降低。

2、高分子鏈的規整性：一般考慮含有不對稱中心的高分子或者具有順反異夠的高分子，規整性好，容易結晶。

3、分子間作用力：分子間能形成氫鍵時，有利於穩定結晶結構。

例如：PVA為非結晶性聚合物，但是水解後，得到的聚乙烯醇卻能結晶，這是因為氫鍵的作用。

(9)聚合物合金為什麼要結晶擴展閱讀

聚合物在不同條件下結晶時，可能得到的結晶形態：單晶、樹枝晶、球晶、纖維狀晶、串晶、柱晶、伸直鏈晶體。形態特徵為：

（1）單晶：分子鏈垂直於片晶平面排列，晶片厚度一般只有10nm左右；

（2）樹枝晶：許多單晶片在特定方向上的擇優生長與堆積形成樹枝狀；

（3）球晶：呈圓球狀，在正交偏光顯微鏡下呈現特有的黑十字消光，有些出現同心環；

（4）纖維狀晶：晶體呈纖維狀，長度大大超過高分子鏈的長度；

（5）串晶：在電子顯微鏡下，串晶形如串珠；

（6）柱晶：中心貫穿有伸直鏈晶體的扁球晶，呈柱狀；

（7）伸直鏈晶體：高分子鏈伸展排列晶片厚度與分子鏈長度相當。