SYNTHETIC POLYMERS: PROPERTIES, TYPES AND EXAMPLES - CHEMISTRY - 2025

The synthetic polymers are those produced by the human hand in the laboratory or industrial scales. Structurally, they consist of the union of small units, called monomers, that link to form what is known as a polymer chain or network.

The lower upper one illustrates the "spaghetti" type polymeric structure. Each black dot represents a monomer, linked to another by a covalent bond. The succession of points results in the growth of the polymer chains, whose identity will depend on the nature of the monomer.

Furthermore, the vast majority of its monomers are derived from petroleum. This is achieved through a series of processes that consist of reducing the size of hydrocarbons and other organic species to obtain small and synthetically versatile molecules.

Properties

Just as the possible structures of polymers are diverse, so are their properties. These go hand in hand with linearity, branching (absent in the image of the chains), the bonds and the molecular weights of the monomers.

However, despite the fact that there are structural patterns that define the property of a polymer - and therefore its type - most have some properties and characteristics in common. Some of these are:

- They have relatively low production costs, but high recycling costs.

- Due to the large volume that their structures can occupy, they are not very dense materials and, in addition, mechanically very resistant.

- They are chemically inert, or sufficient to resist the attack of acidic (HF) and basic (NaOH) substances.

- Lack of conduction bands; therefore, they are poor conductors of electricity.

Types

Polymers can be classified based on their monomers, their polymerization mechanism, and their properties.

A homopolymer is one that consists of monomeric units of a single type:

100A => AAAAAAA…

While a copolymer is one that is made up of two or more different monomeric units:

20A + 20B + 20C => ABCABCABC…

The above chemical equations correspond to polymers synthesized via addition. In these, the polymer chain or network grows as more monomers bind to it.

On the other hand, for polymers via condensation, the monomer binding is accompanied by the release of a small molecule that "condenses":

A + A => AA + p

AA + A => AAA + p…

In many polymerizations p = H ₂ O, as occurs with polyphenols synthesized with formaldehyde (HC ₂ = O).

According to their properties, synthetic polymers can be classified as:

Thermoplastics

They are linear or slightly branched polymers, whose intermolecular interactions can be overcome by the effect of temperature. This results in their softening and molding, and makes them easier to recycle.

Thermostable

Unlike thermoplastics, thermoset polymers have many branches in their polymer structures. This allows them to withstand high temperatures without deforming or melting, due to their strong intermolecular interactions.

Elastomers

They are those polymers capable of withstanding an external pressure without breaking, deforming but then returning to its original shape.

This is because their polymer chains are connected, but the intermolecular interactions between them are weak enough to give way under pressure.

When this occurs, the distorted material tends to arrange its chains in a crystalline arrangement, "slowing down" the movement caused by pressure. Then, when this disappears, the polymer returns to its original amorphous arrangement.

Fibers

They are polymers with low elasticity and extensibility thanks to the symmetry of their polymer chains and the great affinity between them. This affinity allows them to interact strongly, forming a linear crystalline arrangement resistant to mechanical work.

This type of polymer finds use in the manufacture of fabrics such as cotton, silk, wool, nylon, etc.

Examples

Nylon

Nylon is a perfect example of a fibrous-type polymer, which finds many uses in the textile industry. Its polymer chain consists of a polyamide with the following structure:

This chain corresponds to the structure of nylon 6,6. If you count the carbon atoms (gray) starting and ending with those attached to the red sphere, there are six.

Likewise, there are six carbons that separate the blue spheres. On the other hand, the blue and red spheres correspond to the amide group (C = ONH).

This group is capable of interacting through hydrogen bonds with other chains, which can also adopt a crystalline arrangement thanks to their regularities and symmetries.

In other words, nylon has all the properties necessary to qualify as a fiber.

Polycarbonate

It is a transparent plastic polymer (mainly thermoplastic) with which windows, lenses, ceilings, walls, etc. are made. The image above shows a greenhouse made with polycarbonates.

What is its polymeric structure like and where does the name polycarbonate come from? In this case, it does not refer strictly to the anion CO ₃ ^2-, but to this group participating in covalent bonds within a molecular chain:

Thus, R can be any type of molecule (saturated, unsaturated, aromatic, etc.), resulting in a wide family of polycarbonate polymers.

Polystyrene

It is one of the most common polymers in daily life. The plastic cups, toys, computer and television items, and the mannequin head in the image above (as well as other objects) are made of polystyrene.

Its polymeric structure consists of the union of n styrenes, forming a chain with a high aromatic component (the hexagonal rings):

Polystyrene can be used to synthesize other copolymers, such as SBS (Poly (styrene-butadiene-styrene)), which is used in those applications that require a resistant rubber.

Polytetrafluoroethylene

Also known as Teflon, it is a polymer present in many kitchen utensils with an anti-stick action (black pans). This allows food to be fried without the need to add butter or other fat.

Its structure consists of a polymer chain "covered" by F atoms on both sides. These F's interact very weakly with other particles, such as greasy ones, preventing them from sticking to the surface of the pan.

References

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5. Yassine Mrabet. (January 29, 2010). Nylon 3D.. Retrieved on May 07, 2018, from: commons.wikimedia.org
6. Educational Portal. (2018). Properties of polymers. Retrieved on May 7, 2018, from: portaleducativo.net
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