Organic Peroxides

Invisible Powers of the Polymer World: Organic peroxides, one of the hidden heroes of the chemical industry, play a critical role in many reactions such as polymerisation, curing and crosslinking. In this article, we will examine the structure of organic peroxides, their working principles, their advantages and how they are used in different fields.

Structure and Working Principle of Organic Peroxides

Organic peroxides are organic molecules containing oxygen-oxygen (O-O) single bond. This bond is weaker than other chemical bonds and is easily broken. As a result of the decomposition of peroxides, highly reactive atoms or molecular fragments called free radicals are formed. These free radicals are the source of the power of organic peroxides.

In polymerisation, the peroxide molecule is decomposed by heat, light or another initiator to form a free radical. The free radical attacks the monomer molecule (the building block of the polymer) and forces it to bind to another monomer molecule. This chain reaction continues until thousands of monomers bind together to form a polymer chain.

Different Roles of Organic Peroxides

• Polymerisation Agent: As mentioned above, organic peroxides initiate free radical polymerisation of monomers into polymers. Different types of peroxides are suitable for polymerisation processes taking place at low or high temperatures. For example, dicumyl peroxide is generally used in polyethylene production, while methyl ethyl ketone peroxide may be preferred for curing epoxy resins.
• Curing Agent: Resins and plastics show fluidity in liquid state. As a result of the reaction initiated by organic peroxides, polymer chains are bonded together and the material hardens and cures. In this way, resins and plastics can maintain the desired shape and become durable.
• Crosslinking Agent: In some polymerisation processes, free radicals generated by peroxides form cross-links that act as bridges between polymer chains. These cross-links provide the formation of the polymer network structure and increase the heat resistance, chemical resistance and mechanical strength of the material. For example, in rubber production, crosslinking improves properties such as abrasion resistance and elasticity.
• Reaction Initiator: Organic peroxides are also used to initiate various chemical reactions other than polymerisation and curing. For example, peroxides are used in the epoxidation reaction, which is the production of ethylene oxide and ethylene glycol, or in the process of making oils acid resistant.

Advantages of Organic Peroxides

• High Reactivity: The fact that peroxides decompose easily and form free radicals due to their structure makes them strong initiators.
• Thermal Suitability: Different types of peroxides can work effectively at low or high temperatures. This property adapts to various polymerisation and curing processes.
• Processability: Organic peroxides can be found in different physical forms (liquid, powder, granule). This provides ease of use and integrability into different production processes.
• Versatility: Peroxides can be used as initiators or catalysts in a wide range of chemical reactions.

Uses of Organic Peroxides

• Plastic and Rubber Production: Organic peroxides are used in the production of many polymers such as polyethylene, polypropylene, polyvinyl chloride (PVC), synthetic rubber.
• Curing of Resin and Composite Materials: Various resin such as epoxy resins, polyester resins and vinylester resins. Resins and composites can be shaped while in liquid form, but need a chemical reaction called curing for the final product. In this reaction, initiators such as organic peroxides cause the resin molecules to bond together and harden. Different types of peroxides offer options in terms of curing time and temperature. UV light, amines and similar substances can also initiate curing. As a result, the cured resin becomes durable and robust.
• Paints and Varnishes: In some paint and varnish formulations, peroxides accelerate curing and provide better adhesion of the paint to the surface. This increases the durability of the paint and shortens the drying time.
• Pharmaceutical and Cosmetic Production: Peroxides are also used for various purposes in the pharmaceutical and cosmetic industry. For example, peroxide-based bleaches can be found in toothpastes and hair lightening products. Peroxides can also be found in the composition of some disinfectants.
• Chemical Synthesis: Organic peroxides are used as initiators or catalysts in many chemical syntheses other than polymerisation and curing. For example, peroxides are needed in the production of polyethylene terephthalate (PET) or in the synthesis of some monomers.
• Cautions in the Use of Organic Peroxides:
• Organic peroxides are strong oxidisers and should not be brought into contact with flammable or explosive materials. Safety precautions should be taken during use, work in well-ventilated areas and strictly follow the manufacturer's instructions. The storage and transport of peroxides must also be carried out according to specially issued regulations. Improper handling or storage can cause serious accidents.