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WHAT ARE ORGANIC PEROXIDES?


Organic peroxides are compounds containing 0-0 bond. The 0-0 bond is called the peroxide group. Organic peroxides may be considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been replaced by organic radicals.

The peroxide bond is one of the weakest bonds in organic molecules. Therefore it is very unstable and easily splits into reactive radicals via homolytic cleavage. For this reason they do not exist in nature in big quantities.

If peroxides are classified according to their substitution hydroperoxides ,acyclic dialkyl peroxides and cyclic peroxides are the main three groups.

ORGANIC PEROXIDES AS INITIATORS FOR POLYMERIZATIONS

Organic peroxides act through the splitting of the ―O―O― bond into free radicals, therebye initiating the polymerization or crosslinking of monomers or polymers.

Organic peroxides are used extensively as a source of free radicals for the polymerization of unsaturated monomer. Polymerization of monomers are initiated by free radicals produced by organic peroxides. Organic peroxides are used for monomers containing double bonds. Therefore they are used in polymers like low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyacrylate, polystyrene (EPS, GPPS, HIPS, SAN) and polybutadiene.

Organic peroxides are also used for the rheological control of polypropylene by using molecule breaking. Or they are used as cross linking of monomers or polymers.

Organic peroxides for the production of LDPE, PVC, PS are shown below.

TYPE OF PEROXIDE

STRUCTURE

EXAMPLES


Dialkylperoxides


R-O-O-R

Dicumylperoxide

Ditertbutylperoxide


Peroxyesters

tertbutylperoxybenzoate

Tertbutyl peroxyneodecanoate

Tertbutylperoxypivalate

tertbutylperoxyisobutyrate


Diacylperoxides

Isononanoyl peroxide (Cat K)

Didecanoylperoxide

Benzoylperoxide

Lauroylperoxide


Peroxydicarbonates

Dimyristylperoxdicarbonate

Di(2-ethylhexyl)peroxydicarbonate

Dicetylperoxdicarbonate

Organic peroxides are available as solids (usually fine powders), liquids or pastes. Some materials, such as water, odourless mineral spirits, and some phthalate esters do not react with organic peroxides and are often used to dilute them. These solvents are called “phelegmatizers”. The diluted mixtures or formulations are less likely to decompose when exposed to heat or physical shock than the undiluted organic peroxide. Dilution makes the unstable peroxides safer to produce, handle, and use.

Organic peroxides are prone to violent decomposition. Safety must be of allmost importance in handling these products. Decomposition can be caused by several factors, but overheating and exposure to metallic impurities must be controlled during handling.

Half-life data is provided for comparison purposes to select among different peroxides for use. Half-life is defined as the time it takes for one half of a given quantity of peroxide in dilute solution to decompose at a given temperature. The decomposition rate is first order and is characterized at a given temperature by the equation -dC/dt=kC where C is peroxide concentration, t is time and k is the first-order rate constant. For convenience in comparing the stability of peroxides in dilute solutions, peroxides are commonly listed according to the temperatures at which they have half-lives of 10 hours or 1 hour. The higher the temperature corresponding to the half-life, the more stable the peroxide. Half-life temperatures can vary based on the manner in which they are determined, especially the solvent used.


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