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Vazo® free radical sources from DuPont provide efficient initiation of many chemical reactions, including:

• acrylic and vinyl polymerizations
• halogenations (brominations)
• oxidations and related chain reactions
• additions of small molecules across olefinic double bonds
• cross-linking

Product Description

The DuPont™ Vazo® free radical sources are substituted azonitrile compounds that thermally decompose to generate two free radicals per molecule. (Nitrogen gas is also generated.) The rate of decomposition is first-order and is unaffected by contaminants such as metal ions. Vazo® free radical sources are used to initiate bulk, solution, and suspension polymerizations. Vazo® products can be used alone, or in combination with other free radical initiators.

For Solvent Systems

DuPont offers four commercial grades: Vazo® 52(G), 64(G), 67(G), and 88(G). The grade number is the Celsius temperature at which the half-life in solution is 10 hours. These grades are:

• Delivered in solid white "noodle" form
• Soluble in a wide variety of solvents (aromatic hydrocarbons and other functional organic compounds)
• Slightly soluble in aliphatic hydrocarbons
• Insoluble in water

For Aqueous Systems

DuPont offers three commercial grades: Vazo® 56 WSP, 56 WSW, and 68 WSP. The grade number is the Celsius temperature at which the half-life in solution is 10 hours. All four of these grades are water-soluble.

Selecting a Grade of Vazo®

Temperature Range

The most important criterion for choosing the correct grade of Vazo® free radical sources is the temperature at which the reaction is to be run. Vazo® FRSs are generally used within a range of 10 to 30°C (18 to 54°F) above the temperature corresponding to the grade number. This range is a rough guideline only. For instance, Vazo® 64 has been used at 125°C (257°F), where the half-life is less than 1 minute.

Half-Life

Half-life (t1/2), expressed in minutes as a function of temperature, varies for each grade of Vazo® according to the formulae below. (T = temperature in °K.)

Vazo® 52: log (t1/2) = 6767 (1/T) - 18.037 (in toluene) Vazo® 64: log (t1/2) = 7142 (1/T) - 18.355 (in toluene) Vazo® 67: log (t1/2) = 7492 (1/T) - 19.215 (in 1,3,5-trimethylbenzene) Vazo® 88: log (t1/2) = 7660 (1/T) - 18.39 Vazo® 56 WSP and 56 WSW: log (t1/2) = 6426 (1/T) - 16.75 (in water) Vazo® 68 WSP: log (t1/2) = 5920 (1/T) - 14.58 (in water)

Solubility

Another factor in choosing a particular grade is solubility. Vazo® 56 WSP, 56 WSW, and 68 WSP are the grades soluble in water. All the other grades are essentially insoluble in water, sparingly soluble in aliphatic hydrocarbons, and soluble in functionalized organic compounds and aromatic hydrocarbons. Vazo® 67 is significantly more soluble in organic solvents and monomers than the other grades. Caution must be used in the handling of highly concentrated solutions to avoid a self-accelerating decomposition.

Use as Blowing Agent

Vazo® free radical sources are used as blowing agents by taking advantage of the nitrogen evolved during decomposition. However, organic by-products are released in addition to the nitrogen.

Benefits of Vazo®

Solvent-Soluble

Solvent-Soluble Vazo® free radical sources offer a number of advantages over organic peroxides.

• More stable than most peroxides, so can be stored under milder conditions and are not shock-sensitive.
• Decompose with first-order kinetics; not sensitive to metals, acids, and bases; not susceptible to radical-induced decompositions. This makes Vazo® free radical sources more efficient and predictable than other free radical sources.
• Produce less energetic radicals than peroxides, so there is less branching and cross-linking.
• Are weak oxidizing agents, which lets them be used to polymerize unsaturated amines, mercaptans, and aldehydes without affecting pigments and dyes.
• - Are available in four grades to use over a wide temperature range.

Water-Soluble

Water-Soluble Vazo® free radical sources offer all of the advantages of the solvent-soluble grades, plus these other benefits: narrow molecular weight distribution

• cationic or anionic functionality
• minimal branching
• no sulfur