 |
 |
Polymer Side Chains
Name: Zar
Status: student
Grade:
Location: MN
Question:
What are polymer side chains?
Replies:
Hi Zar,
Many polymer molecules are simply long straight chains of atoms.
Others exhibit "branching" or are said to have side chains. A side
chain is simply a relatively short branch of the polymer molecule that
"sticks out" the side of the long polymer molecule. Take ordinary
polyethylene as an example. The polyethylene molecule is a long chain
of carbon atoms, each having two hydrogen atoms attached. So-called
"High Density Polyethylene" molecules look like this... -CH2-CH2-CH2-
where the chain is hundreds of "CH2" units long.
Low Density Polyethylene (such as used to make Tupperware) is similar,
but its molecules have numerous shorter "CH2" chains that grow out
from the side of the main "CH2" chain, rather like branches that grow
out from the trunk of a tree.
The presence of these side chains can affect the physical properties
of a polymer. In the above example of polyethylene, High Density
Polyethylene, with its near-absence of side chains, is harder, more
abrasion resistant and will withstand higher temperatures, compared to
Low Density Polyethylene, that has numerous molecular branches or side
chains.
Regards,
Bob Wilson
Zar,
Synthetic polymers are normally produced such that most of the atoms are
arranged in a straight line in what is called the "main chain". Every now
and then, a polymer is designed to contain branches -either each repeating
unit containing a short side-branch or the polymerization happens such that
there is a random branching off of the polymerization. These side-branches
off the main chain are called "side chains" and they can have a strong
effect on the physical and chemical properties of the polymer.
Greg (Roberto Gregorius)
A typical polymer consists of a backbone and side chains. Side chains are
atoms or groups of atoms that are connected to the polymer backbone. If you
have a single-carbon backbone, each carbon molecule is bonded to two other
carbons (one to each side) along the backbone. Since carbon can have four
bonds, that leaves two additional bonds for side chains. You can add
different atoms to give the polymer different properties. Compare
polyethylene to polytetrafluoroethylene -- PE has very different properties
than PTFE, yet the only difference is that the PE has a hydrogen atom where
PTFE has a fluorine atom. Both have a single-carbon backbone. You can also
connect long chains of molecules to the backbone. If you connect another
polymer, it's known as 'branching'. If you connect one backbone to another,
it's called 'cross-linking'. Biological polymers in particular rely on the
chemistry of side chains. Proteins monomers are known as amino acids. Amino
acid polymers (proteins) have the same backbone, but have different side
chains. The different side chains determine the properties and function of
the protein.
Hope this helps,
Burr Zimmerman
Polymers are typically made up of a main chain of long strands of monomer
units -- from ten to millions. A pot of spaghetti is not a bad example.
Frequently, polymers form branches off the main. These are called "side
chains". There may be a few or many. Sometimes even the branches (side
chains) have branches (side chains). In that case the polymer is often
referred to as a network.
Vince Calder
Click here to return to the Material Science Archives
| |
Update: June 2012
|
|
