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Properties of polymers, Difference of Chain growth and Step growth and examples of Polymers, Polymerization

[EDITOR'S NOTE: Other exam topics are: Macromolecules and Polymers, Acid/Base reactions, Redox reactions, environmental chemistry (ozone depletion), Molecules/Salts/Metals/Atomic lattice, Equilibrium equations and organic chemistry]

Plastic is an everyday material which we encounter in nearly all daily situations. But of what is plastic exactly made?

Advantages of polymers

The age of plastic material has many advantages as it can be tuned very easily (unlike metals for example). Plastic materials can change its colour without any difficulty, are quite elastic and can therefore be used in several areas and its hardness can be altered (by heating the material up and so, it can be reformed easily). The production of such materials is quite inexpensive and the polymers can be combined. This leads to a lot of accessible properties.

Disadvantages of polymers

Most of these plastic materials are not degradable and in the worst case, they cannot be recycled anymore. This leads to waste products which are hard to get rid of. Another disadvantage of using plastic materials is that they descend from crude oil, which might become problematic one day as our resources of crude oil are limited.

Step growth polymerisation

The reaction is quite slow at the beginning and most of the monomers are lost early in the reaction. The molar mass achieved is fairly low compared with chain growth (about 10'000 g/mole). No initiator is needed since chain growth starts spontaneously in presence of an abundant amount of monomers (chains are active).

Graph of step growth polymerisation


Example of a step growth polymerisation (esterification)


Chain growth polymerisation

The reaction starts rapidly at the beginning and high masses are attained at the end of the reaction (about 500'000 g/mole). In order to start such a reaction, an initiator is needed (which has many (at best 7) valence electrons like Iodine for example).

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Graph of chain growth polymerisation


Characteristics and properties of thermoplastics

Thermoplastics possess amorphous (undefined) and crystalline (fixed) parts. As there are less strong intermolecular forces between the amorphous parts they are molten sooner and the thermoplastic becomes easily formable. After cooling, the parts become more defined again. The crystalline parts can also be molten down by continuing the heating process and the thermoplastic can be shaped in even more easily.

Characteristics and properties of thermosetting plastics

Thermosetting polymers show a very high resistance against temperature and mechanical resistance. They can only change their shape by being drilled and treating them with other mechanical appliances.

Characteristics and properties of elastomers

Elastomers can be stretched very easily and get back to their original form without any difficulty. This is due to their few net points where the bonds are connected with each other. This also means that they have a weak resistance against temperature and a weak mechanical consistency.

Properties of polyethene

Polyethene has a bad resistance against temperature and also a bad mechanical consistency. This is due to its weak intermolecular forces which is only a weak induced dipole-dipole force.

Properties of (PVC) polyvinylchloride plastic

Polyvinylchloride has a better temperature resistance as well as a better mechanical consistency. This is mainly due to its stronger induced dipole-dipole forces. The difference to polyethene is that PVC is a bigger molecule and therefore the strength of the induced dipole-dipole force is increased.

Properties of (PET) polyethylene terephthalate

Polyethylene terephthalate, or as it is better known as PET, has a bad temperature resistance, but on the other hand it has a quite good mechanical consistency.

Properties of Nylon (a polycondensation)

Due to its build-up (connection of bonds), it has extremely strong intermolecular forces (dipole-dipole forces) as well as the ability of making hydrogen bonds and it is a very polar molecule as well.

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