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Name: Zar
Status: student
Location: MN

What are polymer side chains?

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.

Bob Wilson


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

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