Allan Hay invented of one of the very few polymerization reactions discovered in the 1960s and 1970s — polymerization by oxidative coupling. High polymers are produced by the copper-catalysed air oxidation of phenols, amines, thiols or ketones. Both the reaction and the mechanism by which it proceeds were new. The discovery stemmed from some of his basic ideas for the direct oxidation of organic compounds, and the research team he led went on to study the mechanism of oxidation.
Allan went on to develop a major high performance plastic (one of only five in production in reasonably large quantities) — polyphenyl oxide (PPO) which is poly(2, 6-dimethyl-1,4 phenylene oxide). In fact, two other polymers in this class have reached the pilot plant stage as a result of the work of his team. Commercially, PPO blended with polystyrene has become the basis of General Electric’s Noryl thermoplastic resins. Allan studied liquid phase oxidation more broadly, in particular devising new processes for the phthalic acids.