Polystyrene

The invention: A clear, moldable polymer with many industrial

uses whose overuse has also threatened the environment.

The people behind the invention:

Edward Simon, an American chemist

Charles Gerhardt (1816-1856), a French chemist

Marcellin Pierre Berthelot (1827-1907), a French chemist

Polystyrene Is Characterized

In the late eighteenth century, a scientist by the name of Casper

Neuman described the isolation of a chemical called “storax” from a

balsam tree that grew in Asia Minor. This isolation led to the first report

on the physical properties of the substance later known as “styrene.”

The work of Neuman was confirmed and expanded upon

years later, first in 1839 by Edward Simon, who evaluated the temperature

dependence of styrene, and later by Charles Gerhardt,

who proposed its molecular formula. The work of these two men

sparked an interest in styrene and its derivatives.

Polystyrene belongs to a special class of molecules known as

polymers.Apolymer (the name means “many parts”) is a giant molecule

formed by combining small molecular units, called “monomers.”

This combination results in a macromolecule whose physical

properties—especially its strength and flexibility—are significantly

different fromthose of its monomer components. Such polymers are

often simply called “plastics.”

Polystyrene has become an important material in modern society

because it exhibits a variety of physical characteristics that can be

manipulated for the production of consumer products. Polystyrene

is a “thermoplastic,” which means that it can be softened by heat

and then reformed, after which it can be cooled to form a durable

and resilient product.

At 94 degrees Celsius, polystyrene softens; at room temperature,

however, it rings like a metal when struck. Because of the glasslike

nature and high refractive index of polystyrene, products made from it are known for their shine and attractive texture. In addition,

the material is characterized by a high level of water resistance and

by electrical insulating qualities. It is also flammable, can by dissolved

or softened by many solvents, and is sensitive to light. These

qualities make polystyrene a valuable material in the manufacture

of consumer products.

Plastics on the Market

In 1866, Marcellin Pierre Berthelot prepared styrene from ethylene

and benzene mixtures in a heated reaction flask. This was the

first synthetic preparation of polystyrene. In 1925, the Naugatuck

Chemical Company began to operate the first commercial styrene/

polystyrene manufacturing plant. In the 1930’s, the Dow Chemical

Company became involved in the manufacturing and marketing of

styrene/polystyrene products. Dow’s Styron 666 was first marketed

as a general-purpose polystyrene in 1938. This material was

the first plastic product to demonstrate polystyrene’s excellent mechanical

properties and ease of fabrication.

The advent ofWorldWar II increased the need for plastics. When

the Allies’ supply of natural rubber was interrupted, chemists sought

to develop synthetic substitutes. The use of additives with polymer

species was found to alter some of the physical properties of those

species. Adding substances called “elastomers” during the polymerization

process was shown to give a rubberlike quality to a normally

brittle species. An example of this is Dow’s Styron 475, which

was marketed in 1948 as the first “impact” polystyrene. It is called

an impact polystyrene because it also contains butadiene, which increases

the product’s resistance to breakage. The continued characterization

of polystyrene products has led to the development of a

worldwide industry that fills a wide range of consumer needs.

Following World War II, the plastics industry revolutionized

many aspects of modern society. Polystyrene is only one of the

many plastics involved in this process, but it has found its way into

a multitude of consumer products. Disposable kitchen utensils,

trays and packages, cups, videocassettes, insulating foams, egg cartons,

food wrappings, paints, and appliance parts are only a few of

the typical applications of polystyrenes. In fact, the production of polystyrene has grown to exceed 5 billion pounds per year.

The tremendous growth of this industry in the postwar era has

been fueled by a variety of factors. Having studied the physical

and chemical properties of polystyrene, chemists and engineers

were able to envision particular uses and to tailor the manufacture

of the product to fit those uses precisely. Because of its low cost of

production, superior performance, and light weight, polystyrene

has become the material of choice for the packaging industry. The

automobile industry also enjoys its benefits. Polystyrene’s lower

density compared to those of glass and steel makes it appropriate

for use in automobiles, since its light weight means that using

it can reduce the weight of automobiles, thereby increasing gas

efficiency.

Impact

There is no doubt that the marketing of polystyrene has greatly

affected almost every aspect of modern society. Fromcomputer keyboards

to food packaging, the use of polystyrene has had a powerful

impact on both the quality and the prices of products. Its use is not,

however, without drawbacks; it has also presented humankind

with a dilemma. The wholesale use of polystyrene has created an

environmental problem that represents a danger to wildlife, adds to

roadside pollution, and greatly contributes to the volume of solid

waste in landfills.

Polystyrene has become a household commodity because it lasts.

The reciprocal effect of this fact is that it may last forever. Unlike natural

products, which decompose upon burial, polystyrene is very

difficult to convert into degradable forms. The newest challenge facing

engineers and chemists is to provide for the safe and efficient

disposal of plastic products. Thermoplastics such as polystyrene

can be melted down and remolded into new products, which makes

recycling and reuse of polystyrene a viable option, but this option

requires the cooperation of the same consumers who have benefited

from the production of polystyrene products.

Polyethylene

The invention: An artificial polymer with strong insulating properties

and many other applications.

The people behind the invention:

Karl Ziegler (1898-1973), a German chemist

Giulio Natta (1903-1979), an Italian chemist

August Wilhelm von Hofmann (1818-1892), a German chemist

The Development of Synthetic Polymers

In 1841, August Hofmann completed his Ph.D. with Justus von

Liebig, a German chemist and founding father of organic chemistry.

One of Hofmann’s students,William Henry Perkin, discovered that

coal tars could be used to produce brilliant dyes. The German chemical

industry, under Hofmann’s leadership, soon took the lead in

this field, primarily because the discipline of organic chemistry was

much more developed in Germany than elsewhere.

The realities of the early twentieth century found the chemical

industry struggling to produce synthetic substitutes for natural

materials that were in short supply, particularly rubber. Rubber is

a natural polymer, a material composed of a long chain of small

molecules that are linked chemically. An early synthetic rubber,

neoprene, was one of many synthetic polymers (some others were

Bakelite, polyvinyl chloride, and polystyrene) developed in the

1920’s and 1930’s. Another polymer, polyethylene, was developed

in 1936 by Imperial Chemical Industries. Polyethylene was a

tough, waxy material that was produced at high temperature and

at pressures of about one thousand atmospheres. Its method of

production made the material expensive, but it was useful as an insulating

material.

WorldWar II and the material shortages associated with it brought

synthetic materials into the limelight. Many new uses for polymers

were discovered, and after the war they were in demand for the production

of a variety of consumer goods, although polyethylene was

still too expensive to be used widely.

Organometallics Provide the Key

Karl Ziegler, an organic chemist with an excellent international

reputation, spent most of his career in Germany. With his international

reputation and lack of political connections, he was a natural

candidate to take charge of the KaiserWilhelm Institute for Coal Research

(later renamed the Max Planck Institute) in 1943. Wise planners

saw him as a director who would be favored by the conquering

Allies. His appointment was a shrewd one, since he was allowed to

retain his position after World War II ended. Ziegler thus played a

key role in the resurgence of German chemical research after the war.

Before accepting the position at the Kaiser Wilhelm Institute,

Ziegler made it clear that he would take the job only if he could pursue

his own research interests in addition to conducting coal research.

The location of the institute in the Ruhr Valley meant that

abundant supplies of ethylene were available from the local coal industry,

so it is not surprising that Ziegler began experimenting with

that material.

Although Ziegler’s placement as head of the institute was an important

factor in his scientific breakthrough, his previous research

was no less significant. Ziegler devoted much time to the field of

organometallic compounds, which are compounds that contain a

metal atom that is bonded to one or more carbon atoms. Ziegler was

interested in organoaluminum compounds, which are compounds

that contain aluminum-carbon bonds.

Ziegler was also interested in polymerization reactions, which

involve the linking of thousands of smaller molecules into the single

long chain of a polymer. Several synthetic polymers were known,

but chemists could exert little control on the actual process. It was

impossible to regulate the length of the polymer chain, and the extent

of branching in the chain was unpredictable. It was as a result of

studying the effect of organoaluminum compounds on these chain

formation reactions that the key discovery was made.

Ziegler and his coworkers already knew that ethylene would react

with organoaluminum compounds to produce hydrocarbons,

which are compounds that contain only carbon and hydrogen and

that have varying chain lengths. Regulating the product chain length

continued to be a problem.

At this point, fate intervened in the form of a trace of nickel left in a

reactor from a previous experiment. The nickel caused the chain

lengthening to stop after two ethylene molecules had been linked.

Ziegler and his colleagues then tried to determine whether metals

other than nickel caused a similar effect with a longer polymeric

chain. Several metals were tested, and the most important finding

was that a trace of titanium chloride in the reactor caused the deposition

of large quantities of high-density polyethylene at low pressures.

Ziegler licensed the procedure, and within a year, Giulio Natta

had modified the catalysts to give high yields of polymers with

highly ordered side chains branching from the main chain. This

opened the door for the easy production of synthetic rubber. For

their discovery of Ziegler-Natta catalysts, Ziegler and Natta shared

the 1963 Nobel Prize in Chemistry.

Consequences

Ziegler’s process produced polyethylene that was much more

rigid than the material produced at high pressure. His product also

had a higher density and a higher softening temperature. Industrial

exploitation of the process was unusually rapid, and within ten years

more than twenty plants utilizing the process had been built throughout

Europe, producing more than 120,000 metric tons of polyethylene.

This rapid exploitation was one reason Ziegler and Natta were

awarded the Nobel Prize after such a relatively short time.

By the late 1980’s, total production stood at roughly 18 billion

pounds worldwide. Other polymeric materials, including polypropylene,

can be produced by similar means. The ready availability

and low cost of these versatile materials have radically transformed

the packaging industry. Polyethylene bottles are far lighter

than their glass counterparts; in addition, gases and liquids do not

diffuse into polyethylene very easily, and it does not break easily.

As a result, more and more products are bottled in containers

made of polyethylene or other polymers. Other novel materials

possessing properties unparalleled by any naturally occurring material

(Kevlar, for example, which is used to make bullet-resistant

vests) have also been an outgrowth of the availability of low-cost

polymeric materials.

Polyester

The invention: Asynthetic fibrous polymer used especially in fabrics.

The people behind the invention:

Wallace H. Carothers (1896-1937), an American polymer

chemist

Hilaire de Chardonnet (1839-1924), a French polymer chemist

John R. Whinfield (1901-1966), a British polymer chemist

A Story About Threads

Human beings have worn clothing since prehistoric times. At

first, clothing consisted of animal skins sewed together. Later, people

learned to spin threads from the fibers in plant or animal materials

and to weave fabrics from the threads (for example, wool, silk,

and cotton). By the end of the nineteenth century, efforts were begun

to produce synthetic fibers for use in fabrics. These efforts were

motivated by two concerns. First, it seemed likely that natural materials

would become too scarce to meet the needs of a rapidly increasing

world population. Second, a series of natural disasters—

affecting the silk industry in particular—had demonstrated the

problems of relying solely on natural fibers for fabrics.

The first efforts to develop synthetic fabric focused on artificial

silk, because of the high cost of silk, its beauty, and the fact that silk

production had been interrupted by natural disasters more often

than the production of any other material. The first synthetic silk

was rayon, which was originally patented by a French count,

Hilaire de Chardonnet, and was later much improved by other

polymer chemists. Rayon is a semisynthetic material that is made

from wood pulp or cotton.

Because there was a need for synthetic fabrics whose manufacture

did not require natural materials, other avenues were explored. One

of these avenues led to the development of totally synthetic polyester

fibers. In the United States, the best-known of these is Dacron, which

is manufactured by E. I. Du Pont de Nemours. Easily made intthreads, Dacron is widely used in clothing. It is also used to make audiotapes

and videotapes and in automobile and boat bodies.

From Polymers to Polyester

Dacron belongs to a group of chemicals known as “synthetic

polymers.” All polymers are made of giant molecules, each of

which is composed of a large number of simpler molecules (“monomers”)

that have been linked, chemically, to form long strings. Efforts

by industrial chemists to prepare synthetic polymers developed

in the twentieth century after it was discovered that many

natural building materials and fabrics (such as rubber, wood, wool,

silk, and cotton) were polymers, and as the ways in which monomers

could be joined to make polymers became better understood.

One group of chemists who studied polymers sought to make inexpensive

synthetic fibers to replace expensive silk and wool. Their efforts

led to the development of well-known synthetic fibers such as

nylon and Dacron.

Wallace H. Carothers of Du Pont pioneered the development of

polyamide polymers, collectively called “nylon,” and was the first

researcher to attempt to make polyester. It was British polymer

chemists John R. Whinfield and J. T. Dickson of Calico Printers Association

(CPA) Limited, however, who in 1941 perfected and patented

polyester that could be used to manufacture clothing. The

first polyester fiber products were produced in 1950 in Great Britain

by London’s British Imperial Chemical Industries, which had secured

the British patent rights from CPA. This polyester, which was

made of two monomers, terphthalic acid and ethylene glycol, was

called Terylene. In 1951, Du Pont, which had acquired Terylene patent

rights for theWestern Hemisphere, began to market its own version

of this polyester, which was called Dacron. Soon, other companies

around the world were selling polyester materials of similar

composition.

Dacron and other polyesters are used in many items in the

United States. Made into fibers and woven, Dacron becomes cloth.

When pressed into thin sheets, it becomes Mylar, which is used in

videotapes and audiotapes. Dacron polyester, mixed with other materials,

is also used in many industrial items, including motor vehicle and boat bodies. Terylene and similar polyester preparations

serve the same purposes in other countries.

The production of polyester begins when monomers are mixed

in huge reactor tanks and heated, which causes them to form giant

polymer chains composed of thousands of alternating monomer

units. If T represents terphthalic acid and E represents ethylene glycol,

a small part of a necklace-like polymer can be shown in the following

way: (TETETETETE). Once each batch of polyester polymer

has the desired composition, it is processed for storage until it is

needed. In this procedure, the material, in liquid form in the hightemperature

reactor, is passed through a device that cools it and

forms solid strips. These strips are then diced, dried, and stored.

When polyester fiber is desired, the diced polyester is melted and

then forced through tiny holes in a “spinneret” device; this process

is called “extruding.” The extruded polyester cools again, while

passing through the spinneret holes, and becomes fine fibers called

“filaments.” The filaments are immediately wound into threads that

are collected in rolls. These rolls of thread are then dyed and used to

weave various fabrics. If polyester sheets or other forms of polyester

are desired, the melted, diced polyester is processed in other ways.

Polyester preparations are often mixed with cotton, glass fibers, or

other synthetic polymers to produce various products.

Impact

The development of polyester was a natural consequence of the

search for synthetic fibers that developed fromwork on rayon. Once

polyester had been developed, its great utility led to its widespread

use in industry. In addition, the profitability of the material spurred

efforts to produce better synthetic fibers for specific uses. One example

is that of stretchy polymers such as Helance, which is a form

of nylon. In addition, new chemical types of polymer fibers were developed,

including the polyurethane materials known collectively

as “spandex” (for example, Lycra and Vyrenet).

The wide variety of uses for polyester is amazing. Mixed with

cotton, it becomes wash-and-wear clothing; mixed with glass, it is

used to make boat and motor vehicle bodies; combined with other

materials, it is used to make roofing materials, conveyor belts,hoses, and tire cords. In Europe, polyester has become the main

packaging material for consumer goods, and the United States does

not lag far behind in this area.

The future is sure to hold more uses for polyester and the invention

of new polymers. These spinoffs of polyester will be essential in

the development of high technology.