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Hazard Predictions

• Generates heat: Exothermic reaction at ambient temperatures (releases heat)
• Intense or explosive reaction: Reaction may be particularly intense, violent, or explosive
• Polymerization hazard: Polymerization reaction may become intense and may cause pressurization

Certain metallocene compounds (consisting of a transition metal ion bound to two cyclopentadienyl groups) actively polymerize ethylene and other hydrocarbons with terminal carbon-carbon double bonds. Particularly active examples are metallocenes containing zirconium, scandium, yttrium, lanthanum, and other lanthanide metals (atomic numbers 58-71). Most of these are polymerization active even in the absence of a cocatalyst (Janiak, C. 2002. Metallocene Catalysts. Kirk-Othmer Encyclopedia of Chemical Technology. (Online)).

Ziegler-Natta catalysts (which include an organometallic part) catalyze the polymerization of dienes (and other olefins). Among the most prominent ones are transition metal-based catalysts including Ziegler or Ziegler-Natta type catalysts. The metals most frequently used are Ti, Mo, Co, Cr, Ni, V, Nd, and other lanthanides (Sun, H. N. and Wristers, J. P. 2002. Butadiene. Kirk-Othmer Encyclopedia of Chemical Technology. (Online)).

Polymerizable: Materials, commonly called monomers, that have the capability to undergo thermally induced or chemically initiated radical type polymerization reactions, which could generate significant amounts of heat (up to -100 kJ/mol) and pressure due to decomposition and formation of gas byproducts. These monomers are mainly the vinyl monomers common to the chemical industry such as styrene and its derivatives (including divinyl benzene), acrylamide and its derivatives, butadiene, acrylonitrile, vinyl acetate, and others. Also included here are the acrylates and acrylic acid derivatives but note that these materials are also captured in this tool in a separate and distinct category due to their unique hazards and their high volume of use in the industry.

These materials typically are inhibited with low ppm levels of antioxidants (inhibitors) to prevent premature polymerization chain reactions. Many of these inhibitors require dissolved oxygen to be effective. Inhibitor depletion is a function of time and temperature, with higher temperatures increasing depletion rates. These materials are known to be susceptible to destabilization due to low ppm levels of contaminants. Radical generating contaminants such as peroxides and azides are known to initiate monomer polymerization; however, the effects of seemingly benign materials are harder to predict. Therefore, extreme caution should be used in any contamination event. And the material should be presumed to be destabilized until testing and consultation with experts. Uncontrolled polymerization reactions can become adiabatic and lead to a serious runaway reaction with high temperatures and pressures. The general hazards of monomers are discussed in Frurip et al., Process Safety Progress (Vol. 14, No. 2) 1995.