What are polymers & where do they come from?

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What Are Polymers & Where Do They Come From?

Polymers {in one form or another} are all around us and in countless different household objects that are used every day. But to identify a material only as  “a polymer” is about as vague as describing an actor as “that one dude in that movie”. The term can be applied to one of many different substances beneath the more general designation of polymer. They comes in innumerable different shapes, sizes, and textures; and serve different purposes. Most chemists agree that a broad definition of polymers is a chemical composed of a series of repeating units. There are naturally occurring polymers like wool, silk, rubber, proteins, and pectin; artificial polymers such as artificial silk; and their closely related descendent synthetic polymers, which are things like nylon, polyester, Teflon, etc.

Polymerization is created through the aptly named process of polymerization, in which smaller molecules called monomers combine chemically to form a larger network of connected molecules called polymers. The chain can be composed of one singular type of material, or several different substances. The general rule it has to consist of at least one hundred monomer molecules in order to be considered a polymer; with properties like elasticity, tensile strength, and the ability to form fibers. What really sets polymerization apart is the formation of covalent chemical bonds between monomers; as opposed something like crystallization, in which large quantities of molecules aggregate due to the influence of a weak intermolecular force. There are two primary classifications of polymerization processes. Condensation polymerization occurs when each step of polymerization is joined by the formation of a simple molecule like water. Addition polymerization use catalysts, which can often have a significant influence on the construction and chemical properties of the polymer.

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Natural polymers have been used by humans for ages, even if the term “polymer” itself hadn’t been coined at the time- it was first used in 1866 by the French chemist Marcellin Berthelot, when he observed that a chemical compound called styrene formed a resinous polymer if heated at 200° for several hours. But that was prefaced by the invention of vulcanized rubber- a combination of natural rubber and sulphur- in 1839. 1907 represented another milestone with the introduction of synthetic rubber by polymerization; and bakelite {a tough and heat resistance plastic}. In 1920, Hermann Staudinger hypothesised the concept of polymers that is more familiar in today’s world; accurately proposing that they were chains composed of monomers. But many rejected his theory, maintaining their belief that the molecules were held together by some undetermined type of force. After working in a lab with his associates tirelessly, Staudinger was able to prove the validity of his statement.

One type of polymer are called elastomers, such as rubber. Rubber is actually a natural polymer. The repeating component is isoprene. It has been used in one form or another for several hundred years or more; but rubber in its modern and most useful form came around in 1823, when Charles Goodyear invented a stronger material by combining natural rubber with sulphur by a process known as vulcanization.

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Then there are plastics- perhaps the most well-known example of polymer. Plastics generally come in one of two different forms- thermoplastics and thermosets. Thermoplastics are softened and formed by the application of heat, and they harden as they cool down to a lower temperature. These are much more commonly found and used in consumer products. On the other hand, thermosets are formed and the molecules are linked as they are heated, and after that point they will never soften or melt by heat again. Polyethylene is one of the most widely-used plastics on the market today- they come in countless different forms and can be used for innumerable different purposes. It can be used to make plastic bags, textiles, insulation materials, coatings, and much more. High-density polyethylenes are often used to make bottle caps, tubing, etc. Towards the end of the 19th century, artificial versions of fabrics like wool and silk were introduced. Many consider this to be the beginning of modern fiber. In most cases, they are at least one hundred times longer in their length over their width. Benefits include the ability to be ironed, a high tensile strength, stiffness, appealing characteristics of fabric, and versatility.

As for processing polymers, there are a few different approaches. With plastics, injection molding and extrusion are two widely-used methods. Injection molding entails heating the plastic to its melting point so that it will flow, and then filling a mold of a product with the molten material.. It is usually forced in with something like a ram or a screw. After the molds are filled and the structure forms, they are cooled. A great advantage of injection molding is the speed and ease of operation, which allow it to be repeated over and over again in a brief amount of time. Extrusion is similar, but it uses a die rather than a mold. The product must have the exact same cross-sectional shape as the die in order for it to work properly. Fibers are created via spinning. This can be accomplished by melting it, by dissolving it into a solvent that can evaporate, or with chemicals if the solvent cannot evaporate. All are essentially the same concept- the material is melted and pushed through a metal dish with many tiny openings, and the filaments that come through the other side are spun and rapidly wound together to form the fabric.

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References:

http://www.britannica.com/science/polymerization

http://plc.cwru.edu/tutorial/enhanced/files/polymers/apps/apps.htm

http://www.polymerexpert.fr/en/presentation/histoire-des-polymeres/

http://humantouchofchemistry.com/the-history-of-polymers.htm

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