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Ionic Chain-Reaction and Complex Coordination Polymerization 175

another old toy, the frisbee. American children fell in love with the hula hoop and the somewhat infe-
rior Phillips material was good enough to give good hula hoops. Demand for these plastic rings was
sufficient to take the Adams plant output for a half year and turn it into hula hoops. Phillips president,

Paul Endacott, was so pleased that he kept a hula hoop in his office to remind him of his “savior.” By

the time that particular wave of hula hoop mania wound down in 1959, the problems in the product
line at the Adam terminal were overcome and Marlex had found new markets. One of the fi rst markets
was the use of PE and PP baby bottles in hospitals to replace the old glass bottles. The Marlex bottles
were less expensive, could be sterilized (remember, both the new PE and PP could be heated to boiling,
o
100 C, without melting), and would not shatter when dropped. The manufacture of Chiffon household
liquid detergent took a chance on using plastic bottles rather than glass to hold their detergent. Their
success caused other manufacturers to change to the lighter, nonbreakable, and less-expensive plastic
containers. Today, PP and PE hold the major share of the container market.
Copying the tubes used to make the hula hoop, plastic tubing for many varied applications, such
as connecting air conditioners and ice makers, took off. Today, the two most used synthetic poly-
mers are PE and PP. New catalysts and production procedures has allowed the physical properties
and varied uses of these “big two” synthetic polymers to be continually increased.
While it was possible to produce syndiotactic-PP (sPP) employing the Ziegler-Natta solid sys-
tems, commercial sPP has only recently become commercial through the use of the soluble metal-
locene catalysts. These materials have a similar T as iPP but they have a different balance between
g
stiffness and toughness.
Atactic or amorphous forms of PP are also used. Initially, atactic PP (aPP) was obtained as a by-
product of the production of iPP. As an inexpensive by-product, it is used as a modifi er for asphalt

for roofing and in adhesives. As the effectiveness of catalyst systems becomes better, less aPP is
available so that today some aPP is intentionally made for these applications.
While PP is often synthesized employing Ziegler-Natta catalyst, today there exists many other
catalysts systems, including the soluble catalysts systems described in 5.6 “Polyethylenes.” Many of
these were developed by Walter Kaminsky and coworkers in 1980. These catalysts contain a Group
IVB metallocene coupled with methylaluminoxane (MAO). By varying the structure of the metal-
locene cocatalyst, it is possible to tailor the tacticity of the product. Thus, for PP, the atactic product
is formed when the simple zirconocene and hafnocene dichlorides are employed; syndiotactic-PP is
produced when a bridged catalyst is employed; and isotactic-PP is produced when another bridged
catalyst is employed.

Stretching a film tends to orientate the polymer chains. Biaxially stretched or oriented PP, BOPP
is strong and clear, resulting in its wide use and producing clear bags and packaging materials. PP is
often used in the construction of cold-weather clothing under-layers, such as long-sleeved shirts and
underwear. It is also used in warm-weather wear because of its ability to remove perspiration from
the skin. It is used in ropes that can float because of the low density of PP. In low-ventilation areas, it

often replaces PVC because it emits less smoke and no dangerous chlorine-containing fumes when
burned. It serves as the suture material in Prolene. Because of its ability to retain color and to form
thin sheets, it is being used to make stationary folders, storage boxes, and the cube stickers for the
Rubik’s cubes. It is also used to construct trading card holders (such as baseball cards) with each
sheet containing pockets for the trading cards. In medicine, it is also used in hernia repair opera-
tions with a small sheet or film of PP placed over the spot of the hernia to prevent reformation of

the surgical hernia.
Expanded PP, EPP, foam is used for radio-controlled model aircraft, automobiles, and trucks by
hobbyists because of the ability of the foam to absorb impacts and its low density.

5.9 POLYMERS FROM 1,4-DIENES

There are three important 1,4-dienes employed to produce commercially important polymers. These
monomers possess a conjugated pi-bond sequence of -C=C-C=C- that readily forms polymers with

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