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We are constantly exposed to polymer products in our everyday lives.
Our clothes are polymers, just as our plastic forks, insulating cups,
two liter plastic bottles, and plastic wrap are as well.
Some people believe that polymers are all man-made. These macromolecules,
as they are sometimes called, have been a part of the natural environment
since the beginning of life on earth. Polysaccharides, proteins, and nucleic
acids are polymers. Natural rubber is also a polymer. Polymer molecules make
up the structural, transport, protective, and reproductive systems of all
living things. Life processes rely on the chemical changes polymers
undergo as they are built up, broken down, or rearranged.
The term polymer comes from the Greek words polus and mer meaning many
parts. Polymers are huge molecules which are made up of repeating units
called monomers. The monomers may be identical or different. One single
polymer is often made up of thousands of monomers linked together.
One of the simplest man-made polymers is polyethylene, which is made
into clear fruit and vegetable bags. Polyethylene is formed by the
covalent bonding of many monomers of ethylene molecules. A typical
polyethylene molecule may have about 25,000 carbon atoms in its chain
and have a molecular weight of 350,000.
The number of monomers that join to form the final long chain is
theoretically infinite. But usually the number of monomer units falls in
the range of 1,000 to 10,000. Molecular weights range from 14,000 to 500,000.
It may come as a surprise to realize that a bowling ball or a tire can be
considered a single giant molecule due to cross-linkages that bond together
all the separate molecules into a giant network. The bowling ball may have
a molecular weight of about 1028 with a tire's molecular weight being even
larger.
Another important way of categorizing polymers is by their behavior
upon being heated. Thermoplastics melt and soften when heated. An example
of this would be the melting of a polyethylene bag, or the fusing of polyester
or nylon fabrics when a hot iron was used. The melting occurs because
individual molecules are not chemically bonded to each other. Held together
by van der Waals forces, polyethylene melts in the 110 -130 degrees Celcius
range. Nylon, held together by hydrogen bonds as well as by van der Waals
forces, melts at 265 degrees Celcius.
That's a lot of stuff don't you think?
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