Azonitriles are organic compounds with a central N2 linking group, as shown in the chemical decomposition scheme below. These compounds are incredibly useful as a free radical source for polymerization initiation because a thermodynamic force drives the release of N2 as nitrogen gas, forming two free radicals from the azonitrile compound.
Benefits of Using an Azonitrile Initiator
You may be asking, why not just use an organic peroxide for free radical initiation? After all, organic peroxides are usually lower in cost. Many choose azonitrile initiators because they offer many functional benefits over organic peroxide initiators, often leading to significant improvements in polymer quality, workplace safety, and ease of use.
Organic peroxides are incredibly volatile chemicals that tend to undergo a rapid exothermic reaction if not stored under precise conditions, leading to workplace hazards through explosion risks. Azonitriles are not shock sensitive and have more convenient temperatures, enabling safer transport than peroxides with similar half-lives. This allows for much safer transport, storage, and use-case scenarios.
Organic peroxides will react with redox-sensitive agents, solvents, and dyes in a reaction medium, creating more reaction condition requirements to use effectively. Azonitriles will not undergo redox reactions and, thus, will not interfere with redox-sensitive reagents. In addition, organic peroxides will undergo radical-induced decomposition and cannibalize other initiators, making the polymerization less efficient. Azonitriles do not decompose in the presence of free radicals but rather only in the presence of heat or light.
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 cross-linking and gives the chemist much more control over the final polymer structure. This makes azonitrile initiators much more useful for specialty polymer and chemical manufacturing.
Vazo™ Free Radical Initiators
Vazo™ Free Radical Initiators are a line of substituted azonitrile compounds from Chemours. These free radicals are ideal for initiating the polymerization of linear polymers with high molecular weight. Vazo™ Free Radical Initiators come in four grades that vary in stability and decomposition temperature.
The right Vazo™ grade for an application is decided by two main factors: the desired reaction temperature and medium.
The most important factor in determining which Vazo™ Free Radical Initiator to use is reaction temperature. The monomers used in the reaction typically determine the reaction temperature. The Vazo™ portfolio has a realistic operating window from 65°C to 140°C. The number in each Vazo™ grade denotes the approximate 10-hour half-life temperature. As a guideline, a suitable Vazo™ grade may be selected based on a reaction temperature range of 10°C–30°C above or below the corresponding grade number.
Solubility of the initiator in the desired reaction medium is critical to polymerization efficiency. All Vazo™ grades are soluble in common reaction mediums like toluene and acetone. However, Vazo™ 67 exhibits better solubility in a broader range of organic solvents.
Need help selecting a grade? Contact us today to have one of our product specialists guide you to the right Vazo™ Free Radical Initiator solution for your application.