bài giảng đại cương về polymer

+ Tơ nilon hay nilon: là sản phẩm trùng ngưng hai loại monome là hexametylđiamin và axit ađipic : Các tơ poliamit có tính chất gần giống tơ thiên nhiên, có độ dai bền cao, mềm mại, nhưng

- Chất phụ: chất tạo màu, chất chống oxi hoá, chất gây mùi thơm.

c) Ưu điểm của chất dẻo:

- Nhẹ (d = 1,05 ¸ 1,5) Có loại xốp, rất nhẹ

- Phần lớn bền về mặt cơ học, có thể thay thế kim loại

- Nhiều chất dẻo bền về mặt cơ học

- Cách nhiệt, cách điện, cách âm tốt

- Nguyên liệu rẻ

d) Giới thiệu một số chất dẻo

- Polietilen (P.E) : Điều chế từ etilen lấy từ khí dầu mỏ, khí thiên nhiên, khí than đá

Là chất rắn, hơi trong, không cho nước và khí thấm qua, cách nhiệt, cách điện tốt

Dùng bọc dây điện, bao gói, chế tạo bóng thám không, làm thiết bị trong ngành sản xuất hoá học, sơn tàu thuỷ

- Polivinyl clorua (P.V.C)

Chất bột vô định hình, màu trắng, bền với dung dịch axit và kiềm

Dùng chế da nhân tạo, vật liệu màng, vật liệu cách điện, sơn tổng hợp, áo mưa, đĩa hát…

- Polivinyl axetat (P.V.A)

Điều chế bằng cách : cho rồi trùng hợp

Dùng để chế sơn, keo dán, da nhân tạo

- Polimetyl acrilat

và polimetyl metacrilat

Điều chế bằng cách trùng hợp các este tương ứng

Là những polime rắn, không màu, trong suốt

Polimetyl acrilat dùng để sản xuất các màng, tấm, làm keo dán, làm da nhân tạo

Polimetyl metacrilat dùng làm thuỷ tinh hữu cơ

- Êbonit: là cao su rắn có tới 25 - 40% lưu huỳnh Dùng làm chất cách điện

- Têflon : rất bền nhiệt, không cháy, bền với các hoá chất Dùng trong công nghiệp hoá chất và kỹ thuật điện

2 Cao su

Cao su là những vật liệu polime có tính đàn hồi, có ứng dụng rộng rãi trong đời sống và trong kỹ thuật

a) Cao su thiên nhiên: được chế hoá từ mủ cây cao su.

- Thành phần và cấu tạo: là sản phẩm trùng hợp isopren

n từ 2000 đến 15000

- Mạch polime uốn khúc, cuộn lại như lò xo, do đó cao su có tính đàn hồi

Cao su không thấm nước, không thấm không khí, tan trong xăng, benzen, sunfua cacbon

- Lưu hoá cao su: Chế hoá cao su với lưu huỳnh để làm tăng những ưu điểm của cao su như: không bị dính ở nhiệt độ cao, không bị dòn ở nhiệt độ thấp

Lưu hoá nóng: Đung nóng cao su với lưu huỳnh

Lưu hoá lạnh: Chế hoá cao su với dung dịch lưu huỳnh trong CS2

Khi lưu hóa, nối đôi trong các phân tử cao su mở ra và tạo thành những cầu nối giữa các mạch polime nhờ các nguyên tử lưu huỳnh, do đó hình thành mạng không gian làm cao

su bền cơ học hơn, đàn hồi hơn, khó tan trong dung môi hữu cơ hơn

b) Cao su tổng hợp:

- Cao su butađien (hay cao su Buna)

Là sản phẩm trùng hợp butađien với xúc tác Na

Cao su butađien kém đàn hồi so với cao su thiên nhiên nhưng chống bào mòn tốt hơn

- Cao su isopren

Có cấu tạo tương tự cao su thiên nhiên, là sản phẩm trùng hợp isopren với khoảng 3000

- Cao su butađien - stiren

Có tính đàn hồi và độ bền cao:

- Cao su butađien - nitril: sản phẩm trùng hợp butađien và nitril của axit acrilic

Do có nhóm C º N nên cao su này rất bền với dầu, mỡ và các dung môi không cực

3 Tơ tổng hợp:

a) Phân loại tơ:

Tơ được phân thành:

- Tơ thiên nhiên: có nguồn gốc từ thực vật (bông, gai, đay…) và từ động vật (len, tơ tằm…)

- Tơ hoá học: chia thành 2 loại

+ Tơ nhân tạo: thu được từ các sản phẩm polime thiên nhiên có cấu trúc hỗn độn (chủ yếu

là xenlulozơ) và bằng cách chế tạo hoá học ta thu được tơ

+ Tơ tổng hợp: thu được từ các polime tổng hợp

b) Tơ tổng hợp:

- Tơ clorin: là sản phẩm clo hoá không hoàn toàn polivinyl clorua

Hoà tan vào dung môi axeton sau đó ép cho dung dịch đi qua lỗ nhỏ vào bể nước, polime kết tủa thành sợi tơ Tơ clorin dùng để dệt thảm, vải dùng trong y học, kỹ thuât

Tơ clorin rất bền về mặt hoá học, không cháy nhưng độ bền nhiệt không cao

- Các loại tơ poliamit: là sản phẩm trùng ngưng các aminoaxit hoặc điaxit với điamin Trong chuỗi polime có nhiều nhóm amit - HN - CO - :

+ Tơ capron: là sản phẩm trùng hợp của caprolactam

+ Tơ enan: là sản phẩm trùng ngưng của axit enantoic

+ Tơ nilon (hay nilon): là sản phẩm trùng ngưng hai loại monome là hexametylđiamin

và axit ađipic

:

Các tơ poliamit có tính chất gần giống tơ thiên nhiên, có độ dai bền cao, mềm mại, nhưng thường kém bền với nhiệt và axit, bazơ Dùng dệt vải, làm lưới đánh cá, làm chỉ khâu

- Tơ polieste: chế tạo từ polime loại polieste Ví dụ polietylenglicol terephtalat

Tơ lapsan rất bền cơ học, bền

An ion-exchange resin or ion-exchange polymer[1] is an insoluble matrix (or support structure) normally in the form of small (1–2 mm diameter) beads, usually white or yellowish, fabricated from an organic polymer substrate The material has highly

developed structure of pores on the surface of which are sites with easily trapped and released ions The trapping of ions takes place only with simultaneous releasing of other ions; thus the process is called ion-exchange There are multiple different types of ion-exchange resin which are fabricated to selectively prefer one or several different types of ions

Ion exchange resin beads

Ion-exchange resins are widely used in different separation, purification, and

decontamination processes The most common examples are water softening and water purification In many cases ion-exchange resins were introduced in such processes as a more flexible alternative to the use of natural or artificial zeolites

Most typical ion-exchange resins are based on crosslinked polystyrene The required active groups can be introduced after polymerization, or substituted monomers can be used For example, the crosslinking is often achieved by adding 0.5-25% of

divinylbenzene to styrene at the polymerization process Non-crosslinked polymers are used only rarely because they are less stable Crosslinking decreases ion- exchange capacity of the resin and prolongs the time needed to accomplish the ion exchange processes Particle size also influences the resin parameters; smaller particles have larger outer surface, but cause larger head loss in the column processes

Besides being made as bead-shaped materials, ion exchange resins are produced as membranes The membranes are made of highly cross-linked ion exchange resins that allow passage of ions, but not of water, are used for electrodialysis

There are four main types differing in their functional groups:

• strongly acidic (typically, sulfonic acid groups, e.g sodium polystyrene sulfonate

or polyAMPS)

• strongly basic, (quaternary amino groups, for example, trimethylammonium groups, e.g polyAPTAC)

• weakly acidic (mostly, carboxylic acid groups)

• weakly basic (primary, secondary, and/or ternary amino groups, e.g polyethylene amine)

There are also specialised types:

• chelating resins (iminodiacetic acid, thiourea, and many others)

o 1.3 Production of high purity water

o 1.4 Ion-exchange in metal separation

[ edit ] Water softening

Main article: Water softening

In this application, ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions When the resin is fresh, it contains sodium ions at its active sites When in contact with a solution containing magnesium and

calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in

solution by sodium ions This process reaches equilibrium with a much lower

concentration of magnesium and calcium ions in solution than was started with

The resin can be recharged by washing it with a solution containing a high concentration

of sodium ions (e.g it has large amounts of common salt (NaCl) dissolved in it) The calcium and magnesium ions migrate off the resin, being replaced by sodium ions from the solution until a new equilibrium is reached

This is the method of operation used in dishwashers that require the use of 'dishwasher salt' The salt is used to recharge an ion-exchange resin which itself is used to soften the water so that limescale deposits are not left on the cooking and eating utensils being washed

[ edit ] Water purification

In this application, ion-exchange resins are used to remove poisonous (e.g copper) and heavy metal (e.g lead or cadmium) ions from solution, replacing them with more

innocuous ions, such as sodium and potassium

Few ion-exchange resins remove chlorine or organic contaminants from water - this is usually done by using an activated charcoal filter mixed in with the resin There are some ion-exchange resins that do remove organic ions, such as MIEX (magnetic ion-exchange) resins Domestic water purification resin is not usually recharged - the resin is discarded when it can no longer be used

[ edit ] Production of high purity water

Water of highest purity is required for electronics, scientific experiments, production of superconductors, and nuclear industry, among others Such water is produced using ion-exchange processes or combinations of membrane and ion-exchange methods Cations are replaced with hydrogen ions using cation-exchange resins; anions are replaced with hydroxyls using anion-exchange resins The hydrogen ions and hydroxyls recombine producing water molecules Thus, no ions remain in the produced water The purification process is usually performed in several steps with "mixed bed ion-exchange columns" at the end of the technological chain

[ edit ] Ion-exchange in metal separation

Ion-exchange processes are used to separate and purify metals, including separating uranium from plutonium and other actinides, including thorium; and lanthanum,

neodymium, ytterbium, samarium, lutetium, from each other and the other lanthanides There are two series of rare earth metals, the lanthanides and the actinides, both of which families all have very similar chemical and physical properties Ion-exchange is the only practical way to separate them in large quantities This application was developed in the 1940's by Frank Spedding

A very important case is the PUREX process (plutionium-uranium extraction process) which is used to separate the plutonium and the uranium from the spent fuel products from a nuclear reactor, and to be able to dispose of the waste products Then, the

plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel and nuclear weapons.

The ion-exchange process is also used to separate other sets of very similar chemical elements, such as zirconium and hafnium, which incidentally is also very important for the nuclear industry Zirconium is practically transparent to free neutrons, used in

building reactors, but hafnium is a very strong absorber of neutrons, used in reactor control rods

[ edit ] Catalysis

In chemistry ion-exchange resins are known to catalyze organic reactions See for

instance self-condensation

[ edit ] Juice Purification

Ion-exchange resins are used in the manufacture of fruit juices such as orange juice where they are used to remove bitter tasting components and so improve the flavor This allows poorer tasting fruit sources to be used for juice production

[ edit ] Sugar Manufacturing

Ion-exchange resins are used in the manufacturing of sugar from various sources They are used to help convert one type of sugar into another type of sugar, and to decolorize and purify sugar syrups

[ edit ] Pharmaceuticals

Ion-exchange resins are used in the manufacturing of pharmaceuticals, not only for catalyzing certain reactions but also for isolating and purifying pharmaceutical active ingredients Three ion-exchange resins, sodium polystyrene sulfonate, colestipol, and cholestyramine, are used as active ingredients Sodium polystyrene sulfonate is a strongly acidic ion-exchange resin and is used to treat hyperkalemia Colestipol is a weakly basic ion-exchange resin and is used to treat hypercholesterolemia Cholestyramine is a

strongly basic ion-exchange resin and is also used to treat hypercholesterolemia

Colestipol and cholestyramine are known as bile acid sequestrants

Ion-exchange resins are also used as excipients in pharmaceutical formulations such as tablets, capsules, and suspensions In these uses the ion-exchange resin can have several different functions, including taste-masking, extended release, tablet disintegration, and improving the chemical stability of the active ingredients

[ edit ] See also

• Ion exchange

[ edit ] Notes

1. ^ IUPAC "strongly discourages" the use of the term 'ion-exchange resin' to refer to

an ion-exchange polymer, but it remains very common: International Union of Pure and Applied Chemistry (2004), "Definitions of Terms Relating to Reactions of Polymers and to Functional Polymeric Materials (IUPAC Recommendations

2003)" , Pure Appl Chem. 76 (4): 889–906,

• Ion Exchangers (K Dorfner, ed.), Walter de Gruyter, Berlin, 1991

• C E Harland, Ion exchange: Theory and Practice, The Royal Society of

Retrieved from "http://en.wikipedia.org/wiki/Ion-exchange_resin"

Categories: Polymers | Water | Synthetic resins | Polyelectrolytes

Polymer Solutions

by Susana B Grassino

The importance assigned to polymer solutions, a topic whose discussion has evolved from a mere informative mention in textbooks to whole books exclusively devoted to that subject, has become increasingly notorious

The reasons are based on key factors In the first place, the understanding of the behavior and both physical and chemical properties of macromolecules has been mainly sustained in studies carried out in solution, like for example the

determination of the relative molecular mass, made by viscometry or gel permeation chromatography (GPC) On the other hand, since polymer solutions are highly viscous even at low concentrations, their commercial application includes a wide range of products, from paintings to processed foods.

Therefore, we can then consider polymer solutions as liquid mixtures made of long

macromolecular chains, and small, light molecules of solvent (Grosberg and

Khokhlov, 1997) This, by the way, is not a usual situation The large size of this

chains implies the employ of certain theoretical models, which should take into account, among other things, the numerous and diverse conformations that these flexible structures may assume This particularity is not consistent with a behavior that could be regarded as an "ideal" behavior In addition to these features, it is easily understandable that the studies performed in the evaluation of the physical- chemical properties of macromolecules are focused on dilute solutions, where the chains are separated by long distances, and therefore the interaction between them

is reduced to a minimum This is not taken for the sake of simplicity, but also

because the properties of dilute solutions are governed by the properties of the individual macromolecules In the case of concentrated solutions, the chains are entangled each other, their interaction increases, and in such conditions, the system

is no longer suitable to evaluate the contribution of each macromolecule in

particular

To learn more about Polymer Solutions, just click on any of the following links:

Summary

 What Is "Solubility" And What It Depends On

 Thermodynamic Considerations For Polymer Solubility

 How Polymers Behave In Dilute Solutions

According to Rosen (1982), there is an assembly of general rules for polymer

solubility, based on experimental observations, from which interesting conclusions can be obtained

Thus, it is well known that the dissolution of polymers depends not only on their physical properties, but also on their chemical structure, such as: polarity,

molecular weight , branching, crosslinking degree, and crystallinity The general

principle that states like dissolves like is also appropriate in the case of polymers

Thus, polar macromolecules like poly (acrylic acid), poly (acrylamide) and polyvinyl alcohol, among others, are soluble in water Conversely, nonpolar polymers or

polymer showing a low polarity such as polystyrene , poly(methyl methacrylate) ,

poly(vinyl chloride) , and poly(isobutylene) , are soluble in nonpolar solvents.

On the other hand, the molecular weight of polymers plays an important role in their solubility In a given solvent at a particular temperature, as molecular weight increases, the solubility of a polymer decreases This same behavior is also noticed

as crosslinking degree increases, since strongly crosslinked polymers will inhibit the interaction between polymer chains and solvent molecules, preventing those

polymer chains from being transported into solution.

A similar situation occurs with crystalline macromolecules, although in such a case the dissolution can be forced if an appropriate solvent is available, or warming the polymer up to temperatures slightly below its crystalline melting point (T m ) For example, highly crystalline linear polyethylene (T m = 135ºC) can be dissolved in several solvents above 100ºC Nylon 6,6 (T m = 265ºC), a crystalline polymer which is more polar than polyethylene, can be dissolved at room temperature in the presence

of solvents with enough ability to interact with its chains, through for example, hydrogen bonding Branched polymer chains generally increase solubility, although the rate at which this solubility occurs, depends on the particular type of branching Chains containing long branches, cause dense entanglements making difficult the penetration of solvent molecules Therefore the rate of dissolution in these cases becomes slower than if it was short branching, where the interaction between chains

is practically non-existent.

How a Polymer Gets Dissolved

Keywords

random coil , hydrodynamic volume

As said earlier, the dissolution of a polymer is generally a slow process, which can take even several weeks, depending on the structure and the molecular weight of a given polymer.

When a low molecular weight solute such as sucrose is added to water, the

dissolution process takes place immediately The sugar molecules leave the crystal lattice progressively, disperse in water, and form a solution.

But polymer molecules are rather different They constitute long chains with a large number of segments, forming tightly folded coils which are even entangled to each other Numerous cohesive and attractive both intra and intermolecular forces hold

these coils together, such a dispersion, dipole-dipole interaction, induction, and

hydrogen bonding (Figure 1a).

Based on these features, one may expect noticeable differences in the dissolution behavior shown by polymers Due to their size, coiled shape, and the attraction forces between them, polymer molecules become dissolved quite slowly than low

molecular weight molecules Billmeyer Jr (1975) points out that there are two stages

involved in this process: in the first place, the polymer swelling, and next the dissolution step itself.

When a polymer is added to a given solvent, attraction as well as dispersion forces begin acting between its segments, according to their polarity, chemical

characteristics, and solubility parameter If the polymer-solvent interactions are

higher than the polymer-polymer attraction forces, the chain segment start to absorb solvent molecules, increasing the volume of the polymer matrix, and loosening out from their coiled shape (Figure 1b) We say the segments are now

"solvated" instead of "aggregated", as they were in the solid state.

Figure 1 Schematic representation of the dissolution process for polymer molecules

The whole "solvation-unfolding-swelling" process takes a long time, and given it is influenced only by the polymer-solvent interactions, stirring plays no role in this case However, it is desirable to start with fine powdered material, in order to

expose more of their area for polymer-solvent interactions.

When crystalline, hydrogen bonded or highly crosslinked substances are involved, where polymer-polymer interactions are strong enough, the process does stop at this first stage, giving a swollen gel as a result.

If on the contrary, the polymer-solvent interactions are still strongly enough, the

"solvation-unfolding-swelling" process will continue until all segments are solvated

Thus, the whole loosen coil will diffuse out of the swollen polymer, dispersing into a solution At this stage, the disintegration of the swollen mass can be favored by stirring, which increases the rate of dissolution.

However, once all the chain segments have been dispersed in the solvent phase, they still retain their coiled conformation, yet they are now unfolded, fully solvated, and with solvent molecules filling the empty space between the loosen segments Hence, the polymer coil, along with solvent molecules held within, adopts a spheric or

ellipsoid form, occupying a volume known as hydrodynamic volume of the polymer

coil (Figure 1c).

The particular behavior shown by polymer molecules, explains the high viscosity of polymer solutions Solvent and low molecular weight solutes have comparable molecular size, and the solute does not swell when dissolving Since molecular

mobility is not restricted, and therefore intermolecular friction does not increase drastically, the viscosity of the solvent and the solution are similar But the

molecular size of polymer solutes is much bigger than that of the solvent In the dissolution process such molecules swell appreciably, restricting their mobility, and consequently the intermolecular friction increases The solution in these cases, becomes highly viscous.

Thermodynamic Considerations for

Polymer Solubility

Keywords

hydrogen bond , entropy

The evaluation of certain thermodynamic factors has allowed establishing if a

polymer in a given solvent will dissolve or not Such factors are: the Gibbs free

energy (∆G) and the solubility parameters.