What is it polymerization condensation or addition

Polycondensation

condensation

Condensation is the general term used to describe a chemical reaction in which two molecules combine to form a larger end product while splitting off a smaller product.

Most of the time, the split off product is water. A simple example of such a condensation from biochemistry is the condensation of two amino acids to a dipeptide:

Further details on the subject of "amino acids, peptides and proteins" can be found on the cell biology pages of this homepage. In biochemistry and cell biology there are quite a lot of condensation reactions and also polycondensations when, for example, thousands of glucose molecules combine to form a starch molecule or tens of thousands of nucleodides form a DNA strand.

Polycondensation

So that a Polycondensation can take place, so the meeting many Molecules with splitting off of water or other small molecular products must be the monomers two have functional groups that are able to donate atoms or groups of atoms. OH groups and COOH groups as well as NH are almost predestined for this2-Groups.

polyester

Polyesters are plastics that have become an indispensable part of everyday life. Not only textile fibers such as Trevira, Diolen and so on are polyester, but also PET beverage bottles (lead picture), CDs, DVDs and BlueRays are made from polyesters.

There are basically two ways of producing a polyester. An ester is a combination of an oxygen acid and an alcohol. A polyester consists of many acid and alcohol molecules that are alternately connected to one another. Each alcohol molecule is linked to two acid molecules, so it must have two OH groups. Each acid molecule is linked to two alcohol molecules and must therefore have two COOH groups. So we can produce a very simple polyester (at least in theory) if we couple a dihydric alcohol (e.g. ethane-1,2-diol) with a dicarboxylic acid (e.g. oxalic acid).

The picture above shows a "mini polyester" made of four molecules of glycol (ethane-1,2-diol) and three molecules of oxalic acid. The figure below shows the generalized basic principle of polyester formation.

In the figure, only 5 acid and 4 alcohol molecules have reacted, with a "real" polyester, thousands of such monomers condense.

Has the carboxylic acid three Carboxyl groups (such as citric acid) or the alcohol three OH groups (such as glycerine) can even form branched polyesters, which of course are much more stable than unbranched polyesters.

PET

One of the best-known polyesters is PET, the abbreviation for polyethylene terephthalate. This compound is a polymer made from ethane-1,2-diol (ethylene glycol) and terephthalic acid, a benzene ring with two carboxyl groups.

Here you can see a "mini PET molecule", consisting of four molecules of the dicarboxylic acid and three molecules of the diol. PET is a thermoplastic plastic that became famous primarily for the PET bottles in which almost all beverages are sold today.

You can also draw thin fibers (thermoplastic!) From the PET plastic, which are then sold under the trade name Trevira or Diols known as textile fibers.

Bakelite

The plastic Bakelite was the first polymer that was produced by polycondensation and at the same time one of the oldest plastics of all, because Bakelite was synthesized in 1872. More details ...

Polyamides

Polyamides are formed when a dicarboxylic acid is esterified with a diamine, a double amine.

Here we see the basic principle of this polymerization using the example of a "mini-polyamide" made up of five diol molecules and four diamide molecules.

Well-known polyamide plastics are textile fibers Perlon and nylon, from which not only clothing is made, but also thick ropes and ropes as well as floor coverings. Incidentally, when the polyamide is formed, peptide bonds are formed that are identical to those of the proteins.

nylon

The synthetic fiber nylon (First produced in 1934) is formed by polycondensation of the dicarboxylic acid adipic acid (1,6-hexanedioic acid) and the diamide hexamethylenediamine (1,6-diaminohexane), i.e. very large monomers with six carbon atoms each.

Here you can see the formation of nylon from 1,6-hexanedioic acid and 1,6-diaminohexane. Nylon is a thermoplastic. In its liquid state, the plastic is pressed through fine nozzles and then hardens to form synthetic fibers. The plastic is cooled with liquid nitrogen. The fibers obtained in this way are then carefully (slowly) stretched until the nylon is ready for sale. During this "stretching", the polymer chains align themselves more or less parallel, H-bonds can form between the H atoms of the former amino groups and the O atoms of the former carboxyl groups, so that the stretched nylon thread is significantly more stable than the crude product.

Here you can see the H-bridges between two of these stretched polymer threads.

Polycarbonates

Polycarbonates are obtained from phosgene, a chlorine derivative of carbonic acid in which both OH groups have been replaced by Cl atoms, and a bisphenol, i.e. an alkane derivative with two phenol groups. The simplest bisphenol is bisphenol A, which can be synthesized from phenol and acetone.

The polycondensation product of the two starting materials is called polycarbonate, mainly because phosgene is a carbonic acid derivative and because the salts of carbonic acid are called carbonates. During the condensation reaction, the two chlorine atoms are released; they react with the H atoms of the OH groups to form hydrogen chloride.

Here we see a section of such a polycarbonate polymer. On the one hand, polycarbonates are mechanically very stable, on the other hand they can be made very transparent. Therefore, they are ideal for glasses or CDs and DVDs. Even protective helmets are made from polycarbonates.

Bisphenol A is likely to be hazardous to health

Incidentally, bisphenol A is a substance that keeps making headlines in the press because it poses many health risks. The release of bisphenol A from various plastics is said to be primarily responsible for the reduced fertility of many women and men. There are studies that confirm this assumption, while other studies find no connection - typical for studies that are partly funded by environmental protection associations and partly by industry. At least in 2011 the Federal Ministry of Food, Agriculture and Consumer Protection banned baby bottles containing bisphenol A plastics.

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