Skip to 0 minutes and 6 seconds Polymers are extremely large molecules that are essential to our existence - for example, our bodies contain proteins, which are polymers of amino acids. To make polymers, small molecules, called monomers, need to be joined together. We will see that there are two ways of doing this, one called addition or chain polymerisation, the other called condensation or step-growth polymerisation. Addition polymerisation usually employs alkenes, such as ethene or styrene, which can be linked together using different reaction conditions. In contrast, condensation polymerisation uses monomers containing two functional groups, such as a diol reacting with a dicarboxylic acid to form a polyester.
Skip to 0 minutes and 50 seconds Polyesters have a wide range of uses from clothing to bottles, films, and liquid crystal displays; in sports equipment their uses range from surfboards to canoes, skis and skateboards. The word polymer is obtained from the Greek words for many or ‘poly’ and parts or ‘mer’. So a polymer is a large molecule made up of smaller, repeating units of monomers, or ‘parts’. Polymers can be either naturally occurring, such as cellulose or peptidoglycan, or artificial like nylon or Kevlar. The different monomers used to make a polymer chain will give the polymer its distinctive properties. For example, using many branching alkyl groups in the monomer will result in a flexible, low-density structure.
Skip to 1 minute and 38 seconds If less branching chains are used then the polymers can align themselves closer together and form a more rigid plastic. Using groups that are able to form hydrogen bonds to each other allows for a flexible material, which is extremely tough due to the combined strength of many hydrogen bonds between different polymer chains. Some polymers can consist of more than one type of monomer. These polymers are so-called co-polymers and the arrangement of the different monomers can be alternating, random or in blocks of the same monomer. The properties of the individual monomers can often be applied to those of the overall polymer.
Skip to 2 minutes and 17 seconds For example, a group of hydrophilic monomers, which interact with water, can be bonded to a group of hydrophobic monomers that do not interact with water. This block co-polymer now contains a hydrophilic block and a hydrophobic block. When placed with other polymers of the same type, into water, the polymers will naturally aggregate to form micelles - structures where the hydrophobic monomers are protected from interactions with water by the outer hydrophilic monomers. Research is underway at York to create inversed micelles. That is to say micelles that contain a hydrophilic interior and a hydrophobic exterior allowing for polar molecules to be encapsulated within non-polar solvents. These micelles could have a range of uses.
Skip to 3 minutes and 5 seconds It has been suggested that micelles could be used as a novel form of drug delivery. The drug, protected inside a micelle of co-polymers, can be delivered to the target site more successfully. When the target site is reached an alteration in pH, solubility or external intervention such as application of radiation or other compounds can be used to open the micelle and allow for the medicine held inside to be released directly at the target site. We will now investigate how polymers are used in the sporting industry - to create materials that are tailor-made to be lighter, stronger and more aerodynamic than those traditionally used.
Skip to 3 minutes and 46 seconds In the world of high performance sports every gram that can be shaved off a piece of equipment can mean the difference between a gold or silver medal!
A general introduction to polymers and their use in micelles
Teflon and serendipity
Teflon® is the trademark name for a family of fluorinated polymers that includes poly(tetrafluoroethene), PTFE ([–CF2–CF2–]n). PTFE was first made by accident by the American chemist Roy Plunkett when he was working on the development of new non-toxic refrigerants for the chemical company, DuPont. Plunkett used pressurised cylinders of gaseous tetrafluoroethene (F2C=CF2) in his research and on one occasion, on the morning of 6 April 1938, he found that there was no pressure in the cylinder but it weighed the same as when filled with gas. On opening the cylinder, he found a waxy white solid had formed.
To his surprise, Plunkett found that the F2C=CF2 had polymerized in the bottle to form PTFE. PTFE has some remarkable properties. It is inert to virtually all chemicals as it contains only strong C–F and C–C bonds, and it is considered the most slippery material in existence because the surface is covered with fluorine atoms that do not interact with atoms in other compounds. These properties have made PTFE a particularly useful polymer. PTFE tubes hold cables and wires in aircraft and cars, in medicine it is used in reconstructive and cosmetic facial surgery, and it has become a household name through its use as a coating on non-stick cookware.
Similarly, Bob Gore wasn’t attempting to improve outdoor clothing when he created Gore-Tex®. Working in his father’s Teflon factory in the late 1960s, he was simply trying to make more efficient use of the plastic by stretching it. He found that pulling Teflon filled it with air pockets. The pockets that appeared in his ‘expanded poly(tetrafluoroethene) (ePTFE)’ were 700 times larger than a water vapour molecule but 20,000 times smaller than a droplet. Gore reasoned that if you made a fabric out of ePTFE, you could block out rain while still venting steamy perspiration, with the added bonus of wind protection. Since the first jacket was made in 1977, ePTFE has found use in products ranging from heart patches to space suits.
A significant number of other notable scientific discoveries have, like Teflon, been made by chance, or serendipitiously. This includes the world’s first artificial sweetener, saccharin (which is 300-400 times sweeter than sugar), discovered by Dr James Schlatter, who, when cleaning lab glassware accidentally tasted a powder on his fingers (he had been making saccharin in connection with an anti-ulcer project). Also vulcanised rubber, formed when Charles Goodyear accidentally dropped a mixture of rubber, sulfur, and lead onto a hot stove. More recently, there is Viagra, developed by Pfizer, initially as a new treatment for angina (a heart condition that constricts the vessels that supply the heart with blood). Trials in people were disappointing, but, volunteers started coming back and reporting an unusual side effect!
Are you are aware of any other serendipitous chemical discoveries? If so, which is your favourite?
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