Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Physical Science. Chemical Processes and Tests. What's a polymer? Man-made polymers include plastics like the one composing these water bottles. Sources American Chemistry Council. June 30, Cite This! Try Our Crossword Puzzle! By Sid Perkins. October 13, at am. Polymers are everywhere. Just look around. Your plastic water bottle. The nylon and polyester in your jacket or sneakers.
The rubber in the tires on the family car. Now take a look in the mirror. Many proteins in your body are polymers, too. Consider keratin KAIR-uh-tin , the stuff your hair and nails are made from.
Even the DNA in your cells is a polymer. By definition, polymers are large molecules made by bonding chemically linking a series of building blocks. Think of a polymer as a chain, with each of its links a monomer. Those monomers can be simple — just an atom or two or three — or they might be complicated ring-shaped structures containing a dozen or more atoms.
But in proteins, DNA and other natural polymers, links in the chain often differ from their neighbors. In some cases, polymers form branching networks rather than single chains.
Researchers are experimenting with many different types of polymers, aiming to further medicine development and enhance products we already use. Polymers are also being used to enhance holograms. Scientists at the University of Pennsylvania created a hologram on flexible polymer material called PDMA that was embedded with gold nanorods, according to a study published online in early in the journal Nano Letters. This new hologram device can hold several images instead of just one. Artificial skin made of a silicone polymer may be the future of anti-aging efforts.
In the form of two creams, the polymer may be able to tighten a person's skin, reduce the appearance of wrinkles and diminish under-eye bags, according to a study published May in the journal Nature Materials. Such artificial skin may also be used to help those with skin conditions, such as eczema, or be used as sun block.
Live Science. Co-polymers are very useful as they have the properties of the constituent polymers and thus can be produced for specific purposes. For example, poly phenylethene polystyrene is brittle but when it is co-polymerized with buta-1,3-diene, the latter gives the polymer resilience and strength. Figure 2 Structures of different types of co-polymer.
Figure 3 Different types of co-polymer have different properties. On the right, the medical vials are made of a random co-polymer of ethene and propene which give a flexible and clear material.
Below, the covering of the cable is a block co-polymer of the two alkenes, giving a very tough material with rubber-like properties.
By kind permission of Total. Thermomplastics consist of individual molecules with no covalent bonding between them but held together by intermolecular bonding.
The polymers become soft on warming and can be moulded. They can be repeatedly warmed, softened and remoulded. A list of examples is given in Table 1. Thermosets , on the other hand, have many covalent bonds between the chains, leading to a three-dimensional structure, which can be regarded as a single molecule. They can be moulded by heat and pressure, but once moulded they cannot be remoulded. The most important examples include the plastics made from methanal formaldehyde.
Elastomers are amorphous solids which, as the name suggests, are elastic Table 3. They have coiled chains which can be stretched out but spring back to their original shape when the stretching force is released. Fibres are thin threads which are produced by extruding a molten polymer through a die in which there are small holes. Fibres produced in this way include the polyamides such as nylon , the polyesters such as terylene and poly propene Table 4. Figure 4 After stretching to make a fibre, the crystallite regions are aligned along the axis of the fibre, and this adds strength to it.
Having been extruded and stretched, the polymer molecules become aligned in the direction of the fibre. Any tendency to return to a random orientation is prevented by the strong intermolecular forces between the molecules Figure 4. Fibres are twisted into threads and can then be woven into cloth or imbedded in a plastic to give it much greater strength Table 4. Another way of classifying polymers is by examining their steric structure. Polymers with side chains can be divided into two classes, one stereoregular which has a recurring pattern in terms of stereochemistry and one atactic with no regular structure.
Figure 5 Molecular structures of poly propene. The 'one handed' structure of isotactic poly propene causes the molecules to form helices. This regular form permits the molecules to crystallize to a hard, relatively rigid material, which, in its pure form, melts at K. Atactic chains are completely random in structure and consequently they do not crystallize. High molecular mass atactic poly propene is a rubber-like material.
Stereoregular polymers are produced when using many Ziegler-Natta see below or metallocene catalysts. As discussed above, polymers can be characterised by the method of polymerization, addition and condensation. Many addition polymers are produced by using an organometallic compound, known as a Ziegler-Natta catalyst. They were first developed by Karl Ziegler and Giulio Natta which led to the two chemists being awared the Nobel Prize in for this brilliant work.
Other addition polymers are produced by generating free radicals using a compound, known as an initiator, to catalyse the reaction. Many condensation polymeriztion reactions, in which one or two monomers are the starting materials, also need catalysts.
The catalysts are described in the unit devoted to each condensation polymer. Ziegler-Natta catalysts are organometallic compounds, prepared from titanium compounds with an aluminium trialkyl which acts as a promoter:. The alkene monomer attaches itself to an empty coordination site on the titanium atom and this alkene molecule then inserts itself into the carbon-titanium bond to extend the alkyl chain. This process then continues, thereby forming a linear polymer, poly ethene. The polymer is precipitated when the catalyst is destroyed on addition of water.
Because it is linear, the polymer molecules are able to pack together closely, giving the polymer a higher melting point and density than poly ethene produced by radical initiation.
Figure 6 Illustrating the role of a Ziegler-Natta catalyst.
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