1. What role do synthetic polymers play in everyday life?
2. How does a polymer’s structure affect its physical properties?
1. Polymers are formed through the continuous combination of smaller units,
2. A polymer’s properties depend upon the monomers used to form it.
3. Different polymer structures result in different properties, which dictate their
use and function.
4. The vast array of monomer and polymer combinations results in a broadening
availability of important everyday applications that affect the quality of life
and the environment.
Polymers are substances that would fall into the category of organic chemistry, which is
What is so special about carbon?
So…….what are polymers? Polymers are
large molecules ( ) made
by bonding smaller repeating molecules,
known as , together in chains.
• These monomers are generally carbon-
Before the development of synthetic polymers, people were limited to using natural
substances such as
• Some natural polymers come from vegetable or animal sources, including
• By the turn of the twentieth century, a few chemically treated natural polymers such as
and had become available.
The origin of
• Many of the polymers manufactured for human use are the result the word
of manufacturing processes that begin with the use of plant materials or "plastics"
fossil fuels. Early forms of rubber were manufactured exclusively by using
the sap of rubber plants. While useful, this rubber had some properties
that were not ideal, such as root means
• In the mid 1800s, a man by the name of
accidentally discovered that it is possible to alter the polymer in natural rubber.
By mixing , Goodyear found that it was
possible to make a molecule that is
. Why?? Because of a process called vulcanization, which is:
• It was not until that significant changes took place in the polymer
industry. Once the world went to war, our natural sources were cut off, making the use of
synthetics critical. During this time period, we saw the use of polymers such as
take the place of natural materials that were no longer
available. Since then, the polymer industry has continued to grow and has evolved into one of
the fastest growing industries in the U.S. and in the world.
THE STRUCTURE OF POLYMERS….
Think of a polymer like a chain…..each link of the chain is the “mer” or . Many
common classes of polymers are composed of . These polymers are
specifically made of small units bonded into long chains. makes up the
backbone of the molecule and hydrogen atoms are bonded along the backbone.
Here is a diagram of polyethylene, the
simplest polymer structure.
Even though the basic makeup of many polymers is carbon and hydrogen, other elements can
also be involved. are
other elements that are found in the molecular makeup of polymers.
Based on the size and variation of the polymer, there are different classifications:
Mers joined together in long chains have a linear zigzag
arrangement, which means
There is also the possibility of being cross-linked or
Linear, Branched, and Cross-linked Polymers
The term is used to describe compounds with relatively large molecular
weights formed by linking together many small monomers. Polyethylene, for example, is
formed by polymerizing ethylene molecules.
Polyethylene is called a or polymer
because it consists of a long string of carbon-carbon bonds. These terms are misleading
because the geometry around each carbon atom is tetrahedral and the chain is neither
linear nor straight, as shown in the figure below.
As the polymer chain grows, it folds back on itself in a random fashion to form structures
such as the one shown in the figure below.
Polymers with branches at irregular intervals along the polymer chain are called
(see figure below).
These branches make it difficult for the polymer molecules to pack in a regular array, and
therefore make the polymer less crystalline. contain
branches that connect polymer chains, as shown in the figure below.
At first, adding cross-links between polymer chains makes the polymer more elastic. The
vulcanization of rubber, for example, results from the introduction of short chains of sulfur
atoms that link the polymer chains in natural rubber. As the number of cross-links
increases, the polymer becomes more rigid.
The decision to classify a polymer as branched or cross-linked is based on the extent to
which the side-chains on the polymer backbone link adjacent polymer chains. The easiest
way to distinguish between these categories is to study the effect of various solvents on
the polymer. Branched polymers are often soluble in one or more solvents because it is
possible to separate the polymer chains. Cross-linked polymers are insoluble in all solvents
because the polymer chains are tied together by strong covalent bonds.
Linear and branched polymers form a class of materials known as .
These materials flow when heated and can be molded into a variety of shapes which they
retain when they cool. Heavy cross-linking produces materials known as
. Once the cross-links form, these polymers take on a shape that cannot be
changed without destroying the plastic. The polypropylene used in the plastic chairs that fill
so many classrooms is a thermoplastic; as you lean back on the chair you can feel it give. The
plastic case in which early radios were placed is an example of a thermoset plastic; it had a
tendency to shatter rather than bend if the radio was dropped on the floor.
To make this chain, many links or “mers” are hooked or polymerized together.
•There are two main classifications of polymerization:
1. Addition polymerization
2. Condensation polymerization
CHARACTERISTICS OF POLYMERS….
Every polymer has very distinct characteristics but most polymers have the following
1. Polymers can be very resistant to chemicals.
2. Polymers can be both thermal and electrical insulators.
3. Generally, polymers are very light in mass with varying
degrees of strength.
4. Polymers can be processed in various ways to produce
thin fibers or very intricate parts.
There are two main groups of polymers: &
• A thermoplastic polymer is one that
• A thermoset polymer is one that
Some other possible properties of polymers:
- An elastomer is a type of molecule that exhibits rubber-like qualities
COMMON PLASTICS USED IN PACKAGING….
Polyethylene Terephthalate (PET or PETE):
PET is clear, tough and has good gas and moisture barrier properties. The vast majority of
this plastic ends up in soft drink bottles and blow molded containers, although sheet
applications are increasing. In addition, a small volume of PET is now used outside the
packaging industry for the production of injection molded components such as bicycle mud
guards. Cleaned, recycled PET flakes and pellets are in great demand for spinning fiber for
carpet yarns and producing fiberfill and geotextiles. Other outlets include strapping,
molding compounds and both food and non-food containers.
Qualities: Clarity, strength/toughness, barrier to gas, resistance to grease/oil,
stiffness, resistance to heat.
Uses: Plastic soft drink bottles, mouthwash bottles, peanut butter and salad
Recycled Products: Tote bags, dishwashing liquid containers, clamshells, laser toner
cartridges, picnic tables, hiking boots, lumber, mailbox posts, fencing, furniture,
High Density Polyethylene (HDPE):
HDPE is a relatively straight chain structure, but, as its name implies, exhibits a higher
density. It is naturally milky white in appearance and finds wide application in blow molded
bottles for milk, water and fruit juices. Copolymer HDPE, pigmented with a variety of
colorants, is used for packaging toiletries, detergents and similar products.
Qualities: Stiffness, strength/toughness, low cost, ease of forming, resistance to
chemicals, permeability to gas, ease of processing.
Uses: Milk, water and juice containers, grocery bags, toys, liquid detergent bottles.
Recycled Products: Recycling bins, benches, bird feeders, retractable pens,
clipboards, fly swatters, dog houses, vitamin bottles, floor tile, liquid laundry
Vinyl (Polyvinyl Chloride or PVC):
In addition to its good physical properties, PVC has excellent transparency, chemical
resistance, long-term stability, flammability resistance, good weatherability, flow and
insulatory electrical properties. The diverse slate of vinyl products can be broadly divided
into rigid and flexible materials. Rigid applications, accounting for 60 percent of total vinyl
production, are concentrated in construction markets which include pipe and fittings, siding,
carpet backing and windows. Bottles and packaging sheet are also major rigid markets.
Flexible vinyl is used in wire and cable insulation, film and sheet, floor coverings, synthetic-
leather products, coatings, blood bags, medical tubing and many more applications.
Qualities: Versatility, ease of blending, strength/toughness, resistance to
grease/oil, resistance to chemicals, clarity, low cost.
Uses: Clear food packaging, shampoo bottles.
Recycled Products: Air bubble cushioning, flying discs, decking, film, paneling,
recycling containers, roadway gutters, snowplow deflectors, playground equipment.
Low Density Polyethylene (LDPE):
A plastic used predominantly in film applications due to its toughness, flexibility and relative
transparency. Because of its lower melting point at a given density, it is used in applications
where heat sealing is easily accomplished. LDPE is the preferred resin on older unconverted
film extrusion equipment due to its ease of extrusion. Typically, LDPE is used to
manufacture flexible films such as those used for plastic retail bags and garment dry
cleaning and grocery bags. LDPE is also used to manufacture some flexible lids, and it is
widely used in wire and cable applications for its good insulatory electrical properties and
Qualities: Ease of processing, barrier to moisture, strength/toughness, flexibility,
ease of sealing, low cost.
Uses: Bread bags, frozen food bags, grocery bags.
Recycled Products: Shipping envelopes, garbage can liners, floor tile, furniture, film,
compost bins, paneling, trash cans, landscape timber, mud flaps.
Polypropylene has excellent chemical resistance, is strong and has the lowest density of the
plastics used in packaging. It has a high melting point, yet is readily heat-sealable. In film
form it may or may not be oriented (stretched). It is also relatively inexpensive. PP is found
in everything from flexible and rigid packaging to fibers and large molded parts for
automotive and consumer products.
Qualities: Strength/toughness, resistance to chemicals, resistance to heat, barrier
to moisture, low cost, versatility, ease of processing, resistance to grease/oil.
Uses: Ketchup bottles, yogurt containers and margarine tubs, medicine bottles.
Recycled Products: Signal lights, battery cables, brooms and brushes, ice scrapers,
oil funnels, landscape borders, bicycle racks.
Polystyrene is a very versatile plastic that can be rigid or foamed. General purpose
polystyrene is clear, hard and brittle. On a per-pound basis, it is a very inexpensive resin. It
is a rather poor barrier to oxygen and water vapor and has relatively low melting point.
Typical applications include protective packaging, containers, lids, bottles, trays and
Qualities: Versatility, insulation, ease of processing, low cost, clarity.
Uses: Videocassette cases, compact disc jackets, coffee cups, knives, spoons and
forks, cafeteria trays, grocery store meat trays and fast-food sandwich containers.
Recycled Products: Thermometers, light switch plates, insulation, egg cartons, vents,
desk trays, rulers, license plate frames, concrete.