In 1928 DuPont broke new ground by setting aside a laboratory for pure research and Wallace Carothers, at the age of 32, was placed in charge the research division.
DuPont was aware of the work of Father Julius Nieuwland into the synthesis of chloroprene from acetylene and believed that this could be the precursor of a viable synthetic elastomer (chloroprene has a molecular structure which can be described as that of isoprene
[the building block of natural rubber] with its branch methyl group replaced by a chlorine atom). This became Carothers’ first project and in April 1930 the polymer was synthesised by one of his team, Arnold Collins. This had the anticipated ‘rubbery’ properties but was more like vulcanized natural rubber than the raw (unvulcanized) material. It was designated µ-polychloroprene.
Further experimentation showed that if the polymerization process was carried out under controlled conditions and stopped before it was complete, a material much more akin to unvulcanized natural rubber was obtained (α-polychloroprene) which could be milled, compounded, shaped and then converted to the µ- form just by heating. The process could be accelerated by the addition of metal oxides such as zinc oxide and primary aromatic amines. Enough was known now about how to handle the material for it to be marketed and, whilst some of its properties were poorer than those exhibited by natural rubber, it had a much greater oil and chemical resistance. This gave it a niche market and it went into production in 1931 as Neoprene, the first commercially successful synthetic rubber polymer which is still in production today. The chemical name for the elastomer is polychloroprene, Neoprene being DuPont’s trade name, but, like Hoover, the word has now been accepted as generic.
The early material was still not perfect as it had poor colour, a strong smell and was not particularly stable but these defects were cured with the advent of solution polymerization and a particular advantage was found in that differing polymerization processes gave Neoprenes with differing properties. They also provided a latex which could be used directly for coatings or dipping as well as being coagulated like natural rubber to give the dry material.
Its two properties of oils and chemical resistance led to its being used extensively in the automotive industry for gaskets, belting and hoses (although today more sophisticated elastomers are competing successfully for these applications) as well as for lining tanks which would contain strong organic and inorganic acids.
Its availability as a latex which could be blown to a closed cell foam and then formed into thin sheets virtually overnight gave birth to a new industry – the manufacture of wet suits – which is still one of the major uses of the material today.