Surprise polymerization of methacryloyl chloride

Janice Frazier
IBM-Almaden Research Center, San Jose, Calif.

Chemical & Engineering News (3 Jun 1996) Vol. 74, No. 23, pp. 4.


On Feb. 7, a 100-g container of methacryloyl chloride, originally containing 150-ppm phenothiazine stabilizer, was found to have failed in a storage cabinet. The chemical had been purchased five years ago. The original bottle was in pieces, the largest piece about a quarter of the whole. No adjacent bottles were broken, and the labels of adjacent bottles suffered only from chemical attack of a black goo that erupted from the broken container.

Apparently, the monomer underwent exothermic polymerization to colorless polymethacryloyl chloride, which then underwent thermal degradation to a highly colored material.

The black goo was surprisingly soluble, nonacidic, and odorless. The residual monomer--if any--must have volatilized and gone up the exhaust vent together with any gases generated. Nuclear magnetic resonance confirmed that no monomer was left and suggested that at least the truly soluble component was of low molecular weight.

Records indicate that the container was not refrigerated consistently. We believe that room-temperature storage eventually exhausted the phenothiazine, resulting in runaway polymerization.

Many materials labeled "refrigerate" do not pose a hazard if stored at room temperature; it just means that the chemical loses purity with time. Most chemists try to avoid storing acid chlorides in a refrigerator because of the inevitable corrosion of metal refrigerator parts and because, before use of these chemicals, the container must be carefully warmed to room temperature to minimize hydrolysis. As with most monomers, it was assumed that polymerization - if it occurred - would simply cause a slow increase of viscosity. We now know that methacryloyl chloride may polymerize with no warning, and we recommend that this monomer always be stored cold.

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