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Ionic Chain-Reaction and Complex Coordination Polymerization 167

student working for Carl S. Marvel in 1930 when it was an unwanted by-product from the reaction
of ethylene and a lithium alkyl compound. In 1932, British scientists at the Imperial Chemical
Industries, ICI, accidentally made PE while they were looking at what products could be produced
from the high-pressure reaction of ethylene with various compounds. On March 1933, they found
the formation of a white solid when they combined ethylene and benzaldehyde under high pressure
(about 1,400 atmospheres pressure). They correctly identified the solid as PE. They attempted the

reaction again, but with ethylene alone. Instead of again getting the waxy white solid, they got a
violent reaction and the decomposition of the ethylene. They delayed their work until December
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1935 when they had better high-pressure equipment. At 180 C, the pressure inside of the reaction
vessel containing the ethylene decreased consistently with the formation of a solid. Because they
wanted to retain the high pressure, they pumped in more ethylene. The observed pressure drop
could not be totally due to the formation of PE, but something else was contributing to the pressure
loss. Eventually, they found that the pressure loss was also due to the presence of a small leak that
allowed small amounts of oxygen to enter into the reaction vessel. The small amounts of oxygen
turned out to be the right amount needed to catalyze the reaction of the additional ethylene that was
pumped in subsequent to the initial pressure loss (another “accidental” discovery). The ICI scientists
saw no real use for the new material. By chance, J. N. Dean of the British Telegraph Construction
and Maintenance Company heard about the new polymer. He had needed a material to encompass
underwater cables. He reasoned that PE would be water resistant and suitable to coat the wire pro-
tecting it from the corrosion caused by the salt water in the ocean. In July of 1939, enough PE was
made to coat one nautical mile of cable. Before it could be widely used, Germany invaded Poland

and PE production was diverted to making flexible high-frequency insulated cable for ground and
airborne radar equipment. PE was produced, at this time, by ICI and by DuPont and Union Carbide
for the United States.
Polyethylene did not receive much commercial use until after the war when it was used in the

manufacture of film and molded objects. PE film displaced cellophane in many applications being

used for packaging produce, textiles, and frozen and perishable foods, and so on. This PE was
o
branched and had a relatively low-softening temperature, below 100 C, preventing its use for mate-
rials where boiling water was needed for sterilization.
Karl Ziegler, director of the Max Planck Institute for Coal Research in Muelheim, Germany, was
extending early work on PE, attempting to get ethylene to form PE at lower pressures and tempera-
tures. His group found that certain organometallics prevented the polymerization of ethylene. He
then experimented with a number of other organometallic materials that inhibited PE formation.

Along with finding compounds that inhibited PE formation, they found compounds that allowed the
formation of PE under much lower pressures and temperatures. Further, these compounds produced
a PE that had fewer branches and higher softening temperatures.
The branched PE is called low-density, high-pressure PE because of the high pressures usually
employed for its production and because of the presence of the branches, the chains are not able to
closely pack, leaving voids and subsequently producing a material that had a lower density in com-
parison to low branched PE.
Giulio Natta, a consultant for the Montecatini company of Milan, Italy, applied the Zeigler cata-
lysts to other vinyl monomers such as propylene and found that the polymers were higher density,
higher melting, and more linear than those produced by the then classical techniques such as free
radical initiated polymerization. Ziegler and Natta shared the Nobel Prize in 1963 for their efforts in
the production of vinyl polymers using what we know today as solid-state steroregulating catalysts.

While many credit Natta and Ziegler as first having produced so-called high-density PE and

stereoregular polyolefins, Phillips’ scientists first developed the conditions for producing stereospe-

cifi c olefin polymers and high-density PE. In 1952, J. Paul Hogan and Robert Banks discovered that
ethylene and propylene polymerized into what we today know as high-density PE and stereoregular
PP. As with many other advancements, their initial studies involved other efforts to improve fuel
yields by investigating catalysts that converted ethylene and propylene to higher molecular weight

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