Credit: © 2010 Wiley

Speciality polymer materials often contain additives to improve their properties. These additives can, however, leach out of the material as it ages and become a problem in their own right. Of particular note in this regard are halogenated flame-retardant additives that are known to persist in the environment and bio-accumulate posing a significant health risk. The search for speciality polymers with improved properties without the need for additives is thus an important one. Now, Beom-Young Ryu and Todd Emrick from the University of Massachusetts, Amherst have developed1 a halogen-free self-extinguishing polymer.

The key to the development of non-flammable polymers is an understanding of the mechanism of polymer decomposition. Some aromatic polymers undergo rearrangement reactions as they decompose that result in useful non-flammable properties. Ryu and Emrick were particularly interested in the possibility of introducing a diphenyl triazole structure into polymers — this structure is known to undergo rearrangement to a phenylindole with the release of nitrogen gas at high temperature. First, they prepared a bisphenol substituted triazole — 1,4-bis(4-hydroxyphenyl)-1,2,3-triazole — which they condensed with a diacid chloride to produce a triazole-containing polyester. This first polymer was poorly soluble in common solvents, however, which hampered many of the standard characterization techniques and would make the polymers difficult to process.

Thermal characterization was more promising, showing that the polymers could be classified as being of ultralow flammability. A small change in the phenol substitution pattern of the monomer — to 1,4-bis(3-hydroxyphenyl)-1,2,3-triazole — followed by a similar polymerization produced a polymer with markedly improved solubility while retaining and even improving the flammability characteristics.