It was obvious to all Victorian scientists that man could improve
on nature and as early as 1860 Williams thermally decomposed rubber
and identified “spirit”, “oil” and “tar”
- the “spirit”, or volatile substance, he named isoprene
and correctly gave its elemental composition as C5H8. In 1879
Bouchardat re-combined isoprene to a rubbery material and Tilden
wrote in 1884 of its possible industrial significance (if it could
be synthesised cheaply enough). One of life’s perpetual
In 1900 Kondakoff polymerised 2,3-dimethylbutadiene to obtain
“methyl rubber” and this became the first commercial
rubber when it was produced by Bayer in 1909. Interestingly Tilden
had carried out this reaction some twenty years earlier but possibly
by accident as he never recorded it and his material was only
In 1912 a few car tyres were made of this elastomer and one set
went to Kaiser Wilhelm II. One, at least, of these is still in
existence and was displayed at an exhibition of the history of
rubber which toured Europe during 1995-6.
However, it was still not a commercially viable material so Germany’s
obtained most of its natural rubber from the US. This obviously
ended when the States entered the Great War in 1916 and production
of “methyl rubber” was re-commenced with some 2½
thousand tons being manufactured by the war’s end.
Russia was also active during this period, polymerising many
monomers including 1,4-butadiene in 1910 to give butadiene rubber
(BR), but neither the Russian nor the American synthetic rubber
industries was under the same pressures as Germany and, with the
price of natural rubber low again, there was little incentive
for anything other than academic research.
The situation changed drastically in 1922 when the Stephenson
Reduction Plan was introduced. This was designed to cut production
from the British-controlled plantations and so force up the price
of natural rubber (NR). Over the next three years there was a
ten fold price rise - followed by an equally rapid and catastrophic
fall as producers outside the control of Britain flooded the market.
It was this political intervention in the free market which triggered
the next phase in the development of the synthetics.
One of the first of the new materials was far removed from the
work of the preceding years in that it was prepared, by accident
in the early 20's (although not patented until 1932). This was
an ethylene polysulphide - the first of the ‘Thiokols’
which are still in use as sealants today. Working independently
in Switzerland, Baer produced a similar material in 1926 on which
IG Farbenindustrie based its Perdurens whilst in the States the
thiokol rubbers were referred to as GR-P rubber.
IG (which now included Bayer) had resumed its research in 1925
and soon came on stream with polybutadiene rubber which it called
Buna, as well as two copolymers synthesised by mixing two different
monomers together before the polymerization stage - Buna S (styrene
butadiene rubber, SBR or GR-S in America) and Buna-N (butadiene
acrylonitrile rubber, NBR or GR-A). These had reached laboratory
production by 1930 but were not industrially developed when reaction
to the Stephenson Reduction plan made the price of NR head for
the floor again.
However, in 1933, when Hitler came to power, work restarted with
a vengeance, only now with solution polymerisation, rather than
gas phase polymerisation being the preferred route forward.
Given the political situation in the 30’s it is perhaps
surprising that IG and the Standard Oil Co. of New Jersey formed
a joint study group - although they did maintain carefully identified
areas of privacy. At that time IG was making acetylene, its primary
feedstock for elastomer synthesis, from calcium carbide. This
was a private area but in about 1930 it changed to natural gas
as the primary feedstock - the use of which was a joint area so
Standard Oil became entitled to an interest. This led to Standard
holding the US patents to all the Buna rubbers, a crucial factor
in the development of the American synthetic rubber industry as
the Second World War developed and the output of NR fell essentially
A further valuable material to come out of the IG/Standard agreement
was butyl rubber (IIR). Its precursor was synthesised by IG as
polyisobutylene (IM) and had no olefinic groups so it could not
be vulcanized. Standard added a few % of butadiene (or isoprene)
to give a low level of residual unsaturation and thus a vulcanizable
elastomer; butyl rubber.
Throughout this period all the work in the US was privately funded
and when the Second World War started production was minimal.
It only rose from 2,000 tons in1939 to 10,000 tons in 1941. However,
the first government-owned plant came on stream in mid 1942 and
by 1945 the year’s production exceeded 830,000 tons. Over
this same early period Germany’s production went from 22,000
to a peak of about 100,000 tons in the middle years of the war
and then, not surprisingly, fell to zero in 1945.
There is one other major elastomer which made its appearance
between the wars and this was polychloroprene (CR).
Its origin can be traced to the academic work of Father Julius
Nieuwland in 1922 into the dimerization of acetylene to form vinyl
acetylene. When Du Pont heard of this, it realised that the addition
of hydrogen chloride across the acetylenic bond would produce
2-chloro-1,3-butadiene, a substance structurally similar to isoprene
except that the side chain methyl group had been replaced by a
chlorine atom. This chemical, which they called chloroprene was
polymerised by Carothers and his team in 1930 and in commercial
production the next year as polychloroprene although this is still
more often called by Du Pont’s trade name which was initially
Duprene and later became Neoprene. It was the first really viable
commercial synthetic rubber.
The American contribution to synthetic rubber production during
the war had been a vast amount of fundamental research together
with production technology and plant but, when the war finished
in 1945, the cycle of cheap natural rubber returned, leading yet
again to reduced commercial interest in the synthetics.
It was left to Ziegler and Natta to re-activate the cycle in
the early 50’s when they developed catalysts which enabled
high cis 1,4-polybutadiene to be synthesised. The third phase
of production techniques had arrived. (Gas phase reactions, emulsion
phase and now catalysed stereo-regular emulsion phase.
In the early 1960’s Du Pont echoed the pre-war work of
IG/Standard when, instead of co-polymerizing just ethylene and
propylene to make ethylene prolylene rubber (EPM) with no crosslinking
sites, they included a small amount of ethylene norbornene which
provided, after co-polymerization, olefinic crosslinking sites
and gave us EPDM. It should be noted that this is still an “M”
rubber (see nomenclature of synthetic elastomers) as the main
polymer chain is saturated and the olefinic double bond forms
part of the pendant norbornene group. Butyl rubber is classified
as an “R” type because the residual double bond from
butadiene or isoprene is in the polymer chain itself.
All of the elastomers discussed so far have been either homopolymers,
(that is one monomer polymerised), or random co-polymers of two
(or three) monomers but, when some structure is fed into this
randomness, we get quite different properties.
This is the principle behind some of today’s thermoplastic
elastomers. In these materials there are soft ‘rubbery’
regions to provide extensibility coupled with ‘glassy’
regions which serve as physical network junctions at their operating
temperatures but melt, making the material mouldable (or re-mouldable)
when they are heated. These materials have been around for some
25 years and, in a world where recycling is king, they are taking
an ever-increasing share of the elastomer market with. recent
figures suggesting about 20% of the non-tyre market.
In this brief summary of the synthetics, many materials have
been omitted but one class must be mentioned since it is unique
in containing no carbon. This is the silicone rubbers, introduced
as early as in 1944 and today ubiquitous, being found in almost
every environment from the most hi-tech to every DIY fanatic’s
Although many people think that today’s world is ruled
by synthetics and NR is dead, its output has continued to grow
throughout the last century although certainly the synthetics
have expanded more rapidly as demand for general purpose elastomeric
materials, which can replace the natural material in many applications,
has grown more rapidly the latter can be produced and speciality
elastomers, which are used for a range of dedicated applications
for which natural and general purpose rubbers are not suited,
have been developed. In round figures, there are about 6 million
tons of NR and 9 million tons of synthetics (SR) produced per
year in the late 1990’s.
There is a final thought: most of the major synthetic elastomers
are today made from that finite material – oil. Natural
rubber comes from a renewable resource and chemical treatments
of NR are being investigated and used to enable modified NR to
operate in areas once considered the sole preserves of the synthetics.
The biosynthesis of natural rubber also consumes the greenhouse
gas carbon dioxide and it produces timber as a by-product.
The story of the synthetics vs the natural elastomer is by no