Azonitriles are organic compounds with a central N₂ linking group. These compounds are incredibly useful as a free radical source for polymerization initiation. Because N₂ is so stable on its own there is a thermodynamic force driving to release the nitrogen gas and two free radicals from the azonitrile compound.
Benefits of Using an Azonitrile Initiator
You may be asking, why not just use an organic peroxide? In general, organic peroxides are usually lower cost, however, azonitrile initiators offer many benefits over an organic peroxide initiator.
Organic peroxides are incredibly volatile and have a tendency to undergo a rapid exothermic reaction if not stored under precise conditions. Azonitriles are much more stable and will not explode like an organic peroxide.
Organic peroxides will react with any redox sensitive agents in a reaction medium including solvents and dyes. Azonitriles will not undergo redox reactions and will not interfere with any redox sensitive reagents. In addition, organic peroxides will undergo radical induced decomposition and will cannibalize initiator making the polymerization less efficient. Azonitriles do not decompose in the presence of free radicals only in the presence of heat.
Control Over Polymerization Products
Unlike an organic peroxide, azonitrile initiators do not abstract hydrogen from growing polymer chains. This reduces the chances of branching or crosslinking and gives the chemist much more control over the final polymer structure. This makes azonitrile initiators much more useful for specialty polymer manufacturing.
Vazo™ Free Radical Initiators
Vazo™ Free Radical Initiators are a line of substituted azonitrile compounds from Chemours™. Like the diagram shows above, one Vazo™ molecule will decompose when exposed to heat to release nitrogen gas and two free radicals. These free radicals are ideal for initiating polymerization of high molecular weight, linear polymers. Vazo™ Free Radical Initiators come in four different grades that vary in stability and decomposition temperature.
Once you have decided to use an azo initiator for your reaction selecting the right grade for the job is decided by two main factors; reaction medium and desired reaction temperature.
Solubility of the initiator in the desired reaction medium is critical to polymerization efficiency. All of the Vazo™ grades listed above are soluble in common reaction mediums like toluene and acetone, however, Vazo™ 67 exhibits better solubility in a broader range of organic solvents.
Perhaps the most important factor in determining which Vazo™ Free Radical Initiator to use in reaction temperature. Reaction temperature is typically determined by the monomers being used in the reaction. The Vazo™ portfolio has a realistic operating window from 65°C - 140°C. As a guideline, Vazo™ grades should be used within reaction temperatures 10-30°C above and below the corresponding grade number.
Need help selecting a grade? Contact us today to have one of our product specialists guide you through the selection process for Vazo™ Free Radical Initiators.