History of Polyolefins
1. Polymers at War: Synthetic Rubbers
Natural rubber derived from the rubber tree (Hevea brasiliensis) is a milky suspension of sticky particles in water, termed a latex. The particles were known to be composed of a polymer of isoprene. It was thought early in the 20th century that natural rubber latex was formed in the plant by some form of addition polymerisation in an aqueous system under relatively mild conditions at ambient temperature. This is now known to be incorrect, but it led to the first developments of something like what we know as emulsion polymerisation - a patent was granted in Germany in 1912 for a dispersion polymerisation of isoprene in water with egg albumin or starch as an emulsifier.
The first patents on true emulsion polymerisation were filed in Germany in the 1930s. Prior to the Second World War emulsion polymerisation was something of a scientific curiosity; little was known about its mechanism, and it had only very limited commercial applications; most processes took weeks or months to go to completion.
Rubber prices followed a path similar to that of dot.com stocks in the early years of last century - as you can see, there was little economic incentive to develop a synthetic rubber in the years following the First World War.
During the early 20th century natural rubber was widely used in many applications, including the tyres essential for modern military transport. The major source of natural rubber latex was the plantations of Southeast Asia, which was cut off in December 1941 by the rapid Japanese conquest of that region.
This same offensive led to the United States entering the war. There were only limited stockpiles of natural rubber in that country, far too few to supply the military needs of the Allies.
A select team of researchers from university and industry was formed, with a mission to develop a process for the production of "synthetic rubber", with the properties of natural rubber, which could be applied on a commercial scale. To achieve this they were able to call upon the full resources of the US government and industry.
At its height, the Synthetic Rubber Project was of a comparable scale to the Manhattan Project which developed the first atomic bomb.
In less than two years a polymerisation process was developed which produced material with properties equal or exceeding those of natural rubber. Isoprene itself was found to be an unsatisfactory monomer, but a mixture of styrene and butadiene (both cheap and plentiful) polymerised under the right conditions provided the required polymer properties.
The original product, known as the "Mutual Recipe" (75% butadiene/25% styrene with rosin soap and a small amount of mercaptan (thiol) (known as "OEI" for "One Essential Ingredient") was adopted for large scale production in early 1943. Production reached over 700 000 tonnes in 1945.
During this period of intensive research, the parameters of emulsion polymerisation, the analytical methods needed to follow these reactions, and the requirements for controlling the properties of "synthetic latices" (latices is the plural of latex, except in the USA) on a commercial scale were all established.
After the war the accumulated knowledge and manufacturing facilities were soon put to use in the production of synthetic latices of other monomers (vinyl acetate, acrylics, etc.) which found application in water-based paints, adhesives, inks, etc. At the same time, the production of synthetic rubber has continued to grow.
Meanwhile, patents had been filed in Germany in the 1930s for the similar synthetic rubbers Buna S (a butadiene-styrene copolymer made by emulsion polymerisation) and Buna N (a butadiene-acrylonitrile copolymer). Though these were much more expensive than natural rubber, production was pushed ahead for the very same reasons the American synthetic rubber programme was accelerated - the uncertain access to natural rubber under war conditions.
German industrialist I G Farben constructed a Buna plant at Oswiecim (Auschwitz) to exploit the plentiful slave labour available there. Twenty-five thousand people died in its construction, and the motto "Arbeit Macht Frei" above its gates is remembered as one of the most chilling images of evil from the Third Reich.