|
Neoprene (Polychloroprene)
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.
|