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Grade Selection Guide

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.