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PLASTICS ADDITIVES

5.52 CHAPTER 5

5.10 ORGANIC PEROXIDES

The O:O bond in peroxides is quite unstable.

.
.
RO:OR → RO + OR
While they are difficult to make, ship, store, and handle, the radicals they produce are very
useful in vinyl free-radical polymerization, cure of unsaturated polyesters, cross-linking of
thermoplastics, grafting, and compatibilization of polymer blends.
Stability/reactivity is generally measured by the temperature at which the half-life of
the peroxide is 10 hr, called “the ten-hour half-life temperature.” It is controlled by choice
of the R groups and accelerated by raising the temperature, radiation, catalysis by cobalt
soaps, amines, or redox reaction with reducing agents.

5.10.1 Major Classes of Peroxides
Major classes of peroxides are shown in Fig. 5.13.
5.10.1.1 Acyl Peroxides

• Benzoyl peroxide is the longest-established and most widely used. With 10-hr half-life
at 71°C, it is used to polymerize styrene and other vinyl polymers, for medium-temper-
ature cure of unsaturated polyesters, and for a variety of grafting and compatibilization
reactions.
• Lauroyl peroxide (61°C) is used for somewhat higher reactivity. Its aliphatic structure
also gives lighter color in polymers than can be obtained with the aromatic benzoyl per-
oxide.
• Decanoyl peroxide is used to a lesser extent.
5.10.1.2 Ketone Peroxides. MEK peroxide is used for room-temperature cure of unsat-
urated polyesters. Typical concentrations are 0.5 to 2.0 percent. It may be catalyzed by
0.05 to 0.3 percent of cobalt naphthenate and also further catalyzed by amines.
5.10.1.3 Peroxy Esters. These cover a wide range of reactivities and uses.

• t-butyl peroxy pivalate is a typical low-temperature peroxide.
• t-butyl peroctoate (70°C) is a typical medium-temperature peroxide.
• t-butyl perbenzoate (101°C) is a typical high-temperature peroxide, useful in polymer-
izing styrene and in cure of BMC and SMC unsaturated polyesters.

5.10.1.4 Dialkyl Peroxides. These are typically high-temperature materials.
• Dicumyl peroxide (dicup or DCP) (104°C) is useful in cross-linking LDPE, EVA, EPR,
and EPDM.
• Di-t-butyl peroxide (125°C) is useful for the high-temperature finish of styrene poly-
merization to reduce residual styrene monomer content and thus improve modulus,
HDT, taste, and odor.

5.10.1.5 Hydroperoxides. Hydroperoxides such as cumene hydroperoxide are used pri-
marily for low-temperature emulsion polymerization of butadiene to make “cold rubber.”

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