UNIVERSIDAD NACIONAL AUTÓNOMA DE MÉXICO ESCUELA NACIONAL PREPARATORIA

CONDENSATION POLYMERIZATION REACTIONS

Traditionally, polymers have been classified into two main groups, addition polymers and condensation polymers. This classification, first proposed by Wallace Carothers.

Generally two different reactants or monomers combine with the elimination of a low molecular weight by product such as water, to give a polymer chain.

The corresponding polymerization processes would then be called addition polymerization and condensation polymerization.

Condensation polymerization

Condensation polymerization involves the reaction of a polyfunctional molecule or molecules to give a macro-molecule (polymer) with the loss of some simple molecules such as water or hydrochloric acid. When a bi-functional molecule is used, a lineal condensation product is formed. The following example shows the reaction between a bi functional dihyfric. Alcohol and a dicarboxylic acid.

In the above reaction a polymer molecule is gradually formed until all the functional groups have reacted. It is necessary to have equimolecular proportions of the two monomers and these should be extremely pure; otherwise, the chains would end in the functional group in excess and low molecular weight polymer would be produced. A Third requirement is that the reaction responsible for the polymerization must be a very high yield reaction and the side reactions should be absent, in the following example a hydroxyl acid can condense with itself to form a polymer as follows

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CELLULOSE

The cellulose is a glucose polymer in which the celloboise is the repeating unit. It is a linear polysaccharide that consists of many anhydroglucose units joined by ß-acetal linkages.Also, is a cyclolinear polyether formed by the condensation of sugar molecules; common types of sugar molecules found in cellulose include two cyclic forms of glucose, or glucopyranoses. In cellulose, the glucose residues are condensed via the hydroxyl groups at the 1 and 4 positions on adjacent molecules.It’s an important polysaccharide produced in enormous quantities. Is one of the most abundant compounds in nature. also is very accessible, nontoxic, biodegradable and compatible, and has a low cost.

In plants, is the fibrous substance used as a structural material in grasses, leaves and stems (their cell walls and fibers are made of cellulose).Consists entirely of several thousand ß-D-glucose units linked together by 1,4 acetal bonds between C1 of one sugar and C4 of its neighbor to form one large molecule. Each glucose molecule is joined to the next through the anomeric bond (C1) and the other end of molecule (C4).A typical chain of cellulose is composed of 200 to 6000 anhydroglucose units, each of which contain three hydroxyl groups and are linked by an acetal bridge.

The anomeric bonds that it has are equatorial, this means that the cellulose molecules are linear in general outline, and its rigid structure is thanks the extra hydrogen bonds between the 3-OH groups and the ring oxygen atoms. Their molecules are often present as fibrils because of strong intermolecular hydrogen bonding.Cellulose consists of fully extended chains that are strongly hydrogen-bonded into sheets of a highly crystalline matrix.Contains D-glucopyranoside units linked in (1 → 4), in very long unbranched chains and the linkages in cellulose are ß-glycosidic linkages so they don’t need to coil into helical structures as do glucose polymers when are linked in a α (1 → 4) manner.The linear arrangement of ß-linked glucose units in cellulose presents a uniform distribution of OH groups on the outside of each chain.When two or more cellulose chains make contact, the hydroxyk grouos are ideally situated to zip the chains together forming hydrogen bonds. Making zip many cellulose chains together in this way gives a high insoluble, rigid and fibrous polymer that is ideal as cell-wall material for plants.

A fiber of cellulose may consist of about 40 parallel strands of glucose molecules linked in ß (1 → 4). Each glucose unit in a chain is turned over with respect to the proceding glucose unit, and is held in this position by hydrogen bonds (dashed lines) between the chains. The glucan chains line up laterally to form sheets, and these sheets stack vertically so the can be staggered by one half of a glucose unit.The digestive enzymes of humans cannot attack the ß (1 → 4) linkages because it is very difficult to hydrolyse. Only ruminants, such as cows, whose many stomachs harbor some helpful bacteria, can digest it.

Physical Structure

Cellulose is the most important structural component in plants, and this occurs mainly

Figure 1 Cellulose micro fibril (Taken from http://hrsbstaff.ednet.ns.ca/sdosman/Higher%20level%20BIO/transportinplants9.2.htm)

in the secondary cell wall. The primary cell wall consists mostly oh hemicellulose, with about 8% cellulose and a little pectin. It possesses a netlike structure with limited orientation of the cellulose molecules.

The central lamellae of the cell are similar to pectin, and form the glue between the primary cell walls.

The secondary cell wall contains about 94% cellulose and only grows when the primary cell wall is formed. In it, the cellulose molecules are highly oriented.

Cellulose occurs in various crystalline modifications, which vary slightly in dimensions and angles of the unit cell.

Below is a table showing the Cellulose modifications.

Figure 2 Cell walls (Taken from http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/enzymes-for-aer.html)

ORIGIN UNITS CELL Examples of this Cellulose

Type Natural Artificial A,nm

B,nm

C,nm

Β,deg

Cellulose I (native cellulose)

Ramie, cellulose containing algae

From III with H2O under pressure

0.817

1.034

0.785

84 Cotton,Flax,Hemp,Ramie,Jute.

Cellulose II (hydrated cellulose; regenerated cellulose)

Helicystis algae

Dissolving and reprecipitating cellulose I mercerized fibers.

0.792

1.034

0.908

62 Paper,Parchment,

Cellulose III (Ammoniacal cellulose)

--- Careful degradation of ammoniacal cellulose (from II with NH3)

0.774

1.03

0.99 58 ---

Cellulose IV (high-temperature cellulose)

Colt’s foot

Heating III in glycerine to 290ºC

0.811

1.03

0.791

90 ---

Valonia cellulose

Valonia --- 1.643

1.034

1.57 97

Cellulosederivate

The exact position of the hydrogen bonds in the individual modifications is not known. In cellulose, both glucopyranoses are arranged in the chair form, with the all OH and CH2OH groups arranged equatorially. An intramolecular hydrogen bond exists between O at C-3 and O at C-5. There are seven intermolecular hydrogen bonds.

The various methods used for determining the crystallinity also give different value for cellulose. The variations can be traced to the fact that each method measures a different mean of the density, also that the use of chemical methods of determining crystallinity modifies original physical structure.

Cellulosederivate sind chemische Derivate von Cellulose. Es gibt zahlreiche weitere Modifikationen. Grundlage zur Herstellung von Derivaten sind zumeist hochreine Cellulosen.

Einige Cellulosederivate sind üblich:

Kunstseide

Sie wurde von Hilaire de Chardonnet in Frankreich erfunden und bestand aus Nitrozellulose.

Rayon oder Kunstseide war der erste hergestellte Faser gefunden ist aus einem Polymer hergestellt in der Natur (Cellulose), so gibt es eine synthetische Faser, sondern eine regenerierte Zellulosefaser und gefertigt.

Rayon ist eine sehr vielseitige Faser und hat die gleichen Eigenschaften in Bezug auf die Benutzerfreundlichkeit als andere Naturfasern und kann das Gefühl von Seide, Wolle, Baumwolle oder Leinen imitieren.

Der Rayon ist vor allem in der Kleidung verwendet werden (Blusen, Kleider, Jacken, Unterwäsche, Futterstoffe, Anzüge, Krawatten in Dekor ...), (Kissen, Decken, Polster, deckt in der Industrie ...), (chirurgische Materialien, Produkte Vlies Rahmen Reifen ...) und andere Nutzungen (Damenhygiene-Produkten).

Graf L. M. Hilaire Bernigaud de Chardonnet, der erste Hersteller von Kunstseide

Cellulosehydrat

Cellulosehydrat oder auch Zellglas, bekannt unter dem Namen Cellophan, ist einer der ältesten Kunststoffe für Verpackungen. Es handelt sich um eine dünne, farblose und transparente Folie aus einem Celluloseregenerat.

Cellophan ist durch die Übergabe eines Viskoselösung durch einen schmalen Schlitz in Fällbad zu dünnen Blechen Cellulose produzieren hergestellt. Diese werden mit Glycerin, das ein Weichmacher dient behandelt und beschichtet mit Nitrocellulose, deren Durchlässigkeit zu verringern. Herstellung von Cellophan ist mehr als 150.000.000 £. per Jahr

o Cellophane Eigenschaften:* Hohe Flexibilität und Glanz.* Größere Fähigkeit, Torsion Bemühungen widerstehen.

o Cellulosetrinitrat wird wegen seiner Raucharmut als Hauptbestandteil von rauchschwachem Schießpulver.

o Einige Klebstoffsysteme und Kitte beruhen auf einer Cellulosenitratbasis. (z.B. UHU hart)

Celluloseether

Celluloseether sind in der Regel durch die Einwirkung von Alkali-Zellulose hergestellt (siehe Viskose-Produktion) mit Alkylhalogeniden oder dergleichen (SN2-Reaktionen). Die wichtigsten Ether hergestellt sind Methyl-Cellulose-, Ethyl-Zellulose-, Natrium-Carboxymethylcellulose, eine Hydroxyethyl-Cellulose.Diese Materialien finden Anwendung in der Kunststoffindustrie Bereich und für die Textilveredelung. Natrium Carboxymethylcellulose wird als Verdickungsmittel verwendet Nahrung, zum Beispiel in der von Speiseeis hergestellt. Es ist wichtig, auch in Waschmittelformulierungen, die Verhütung von Verschmutzungen Wiederablagerung auf der Kleidung während des Waschens

Environmental impact The most obvious environmental impacts of pulp production comes from the

Filmband

impact on forests and the products generated in the bleaching. The number of trees consumed depends on the type of paper manufacturing and production process used. It is estimated that it takes about 24 trees to produce one ton of paper using the Kraft process. It is not as efficient as other processes, but has the advantage of producing surplus electricity, which having been produced from biomass, generated a net contribution of carbon dioxide into the atmosphere, a source of heating global. 

BleachWhen the pulp is bleached using elemental chlorine, forming unwanted byproducts such as dioxins and furans. High concentrations of these substances have caused the closure of several fish factories. Improvements in the bleaching process  allows  the total elimination of the use of elemental chlorine to  develop  technologies Elemental Chlorine Free  or  Totally  Chlorine Free

Effluent Liquid effluents are mainly water supply of a population, after being defiled by various applications.  From the point of view of its origin, resulting from a combination  of  liquids  ordebris  carried by water from homes, institutions and commercial and industrial establishments, plus the groundwater, surface water  or  precipitation  that could  be added. Liquid effluents are potentially a major cause of pollution, and that

lignin-containing raw state, high biological oxygen demand, as well as alcohols, chlorates, heavy metals and chelating agents. This impact is reduced to a minimum to the extent that modern plants in a closed cycle working with chemicals, and any water from plants is treated

biologically. In the Kraft process, the effluent produced in the highest proportion of white liquor, which contains chemical pulp and lignin in trees. This is targeted to produce the so-called black liquor, using multi-effect evaporators. The latter is burned in the boilers of the plant,

Paper production

Paper Process

recovering at the bottom of the same pulping chemicals, which are recycled afterwards.  The paper produced from wood pulp can be recycled for four to seven times the limit is imposed by the fiber length, which is becoming less and less each time you reprocess.  To resolve this problem, recycled paper is usually mixed with virgin paper to ensure proper quality paper.  Because of concern for the environment:  the industry  of  paper and cardboard  recycling  is  increasingly  important to recycle 48 to 134 million  tones  which is the same from 23% to 45%

Curious: There are microorganisms (bacteria and fungi) that live in freedom and are also able to hydrolyze cellulose. They have great ecological importance, as recycle cellulosic materials such as paper, cardboard and wood.  Among them, noteworthy is  the  fungus Trichoderma  reesei,  capable  of  producing four  types of cells. Using biotechnology techniques such enzymes are produced that can be used in recycling paper, reducing the cost and pollution.