Oil polymerization

Polymerization processes involve obtaining macromolecules capable of performing predetermined tasks.
The propensity to polymerize is manifested only by products that have unsaturated main bonds.
Polymerization in the case of oil is the thermal thickening of the oil without air.
Oil without any admixtures is boiled at a temperature of 250 ÷ 300 ° C. The thickening of oil here is not due to the absorption of oxygen, as in oxidation, but due to the thickening of oil molecules.
Joining of molecules occurs in three chain stages:

1. The formation of a polymerization nucleus as a result of the collision of several molecules under the influence of temperature.
2. This radical (nucleus) is joined on either side by other monomers or dimers.
3. Completion of the polymerization process occurs when the free bonds at the end of the macromolecule are saturated by cyclization or oxygen attachment. Then the centers that initiate polymerization are rendered inactive.

The process of oil polymerization is a chain transformation, different from normal chemical reactions.
Polymerization can be managed by regulating its rate and the type of final product.
The degree of polymerization of the resulting product is related to its viscosity, tendency to swell, surface tension, structure, as well as other characteristics that affect the paint film.
The basic chemical structure of polymers is divided into three varieties:

• chain (strand),
• lattice,
• three-dimensional.

As the degree of polymerization of oil increases (especially in the lattice structure), the tendency to swell, dissolve and melt decreases. The outward chemical activity of the molecules against other molecules also disappears, making the paint film more resistant to external influences.
The product of polymerization is in a colloidal state, having a chain structure of 50 to 500 monomers. Polymerization does not proceed further.
As a result of polymerization, the oil changes its chemical composition and acquires the following properties:

• it loses its tendency to yellow and turns into a resinous material (linolenic glycerides);
• it becomes impenetrable to gases and water;
• the painting film becomes hard and does not crack.

Painting purposes are best suited to polymerized oil.
It is possible to thicken oil at a lower temperature, for example, oil heated to 150°C for 120 hours (in 10 days) dries slowly and gives a glossy, durable coating.
Oil thickened by various means was used as early as the 9th century. This was done by oxidizing it in air and light or by boiling it.
Oil prepared in this way dried with a sheen that can be seen in medieval paintings.
Most well-preserved works from this period owe their durability precisely to oxidized and polymerized oils.
The only disadvantage of polymerized oil is its rather dark color, which makes it reluctant to use it for painting purposes.