Polymers ObjectivesTo be clear about is what is meant by polymerisationTo understand the range of polymersTo understand key words-

What is a polymer? 1. It is a very large molecules made up of repeating units known as monomers 2. It may be made up of one or more types of monomer 3. It may be natural, e.g. cellulose made up of glucose Or synthetic e.g. polythene made up of ethene units

Important polymers  Plastics  Rubbers  Proteins  Starch  Cellulose  Lignin  Fats  PAHs

Polymers from alkenes One of the reasons why alkenes are so useful is that the unsaturated bonds allow them to polymerise! This involves hydrogenation of the C=C bond. This process gives out energy – is Exothermic Many chemicals can be added in such as oxygen and halogens But the most important is the addition of extra alkenes to form polymers

Addition reactions This is done by heating ethene at high pressure in the presence of oxygen or peroxide. This has to be done by free-radical polymerisation. This cannot be used to produce the useful long chain polymers such as polyethylene. Alkenes can be encouraged to join in the presence of acids such as sulphuric acid to produce dimers or even trimers. This is called cationic polymerization

Polymerisation.

Other important monomers  PVC is poly vinyl chloride. Vinyl chloride is the common name for chloroethene Note how the repeat unit is shown!

Nylon  One of the first polymers synthesised  Made from a di-carboxylic acid and a diamine

Polyacrylamide  Poly 2 propenamide or poly(1-carbamoylethylene)  Repeating units -CH 2 CHCONH 2

Uses of plastics  Plastics have many uses:  There are also many types of plastics  Why do you think plastics are so useful?  What affects which plastic is used, for which purpose?  Do you know what plasticisers are?

Different types of plastics  Plastics divide into two main types: Can you think of examples. Thermosoftening plastics These can be melted and remoulded Thermosetting plastics These set when heated and afterwards cannot be altered.

Why the difference: Bonding  There are two types of bonds  Strong bonds between the monomers within a polymer molecule.  Weaker bonds between the polymer molecules: sometimes called Van der Wals forces.

Thermosoftening  In thermosoftening plastics like poly(ethene) the bonding is like ethane except there are lots of carbon atoms linked together to form long chains. They are moderately strong materials but tend to soften on heating and are not usually very soluble in solvents.  The structure is basically a line of monomers strongly bonded. The polymer molecules are held together by weak intermolecular forces and NOT strong chemical bonds. The long polymer molecules mean the intermolecular forces are appreciable but the material is flexible and softens on heating

Thermosetting  Thermosetting plastic structures like melamine have a 3 dimensional cross-linked giant covalent structure network similar to diamond or silica in principle, but rather more complex and chaotic! Because of the strong 3D covalent bond network they do not dissolve in any solvents and do not soften and melt on heating and are much stronger than thermoplastics

The future of plastics  Modern plastics include bioplastics.  These are made from and or by living organisms.  They may be made by fermentation: Bacteria or other microorganisms mass-produce the biopolymers in bioreactors (fermentation tanks). The biopolymers (lactic acid, polyesters) are extracted from the bioreactors and chemically processed into plastics.  Or by genetic engineering: genes are introduced into plants to make plastics: In 1997, Cargille Dow made a clear plastic (polylactide) from corn. The polylactide fibers woven into sports clothes, upholstery fabrics and bioplastic wraps.

Advantages of Bioplastics  Bioplastics have the advantage of being produced from renewable resources (bacteria, plants) rather than nonrenewable resources (oil, natural gas). Bioplastics are biodegradable -- they can break down in the environment.oil  Bioplastics is a potentially important industry.

Disadvantages of Bioplastics  With current technology, bioplastics might be more expensive to produce, but biotechnology is rapidly advancing and production may become more economical in the future

Plasticisers 1 Increase the plasticity or fluidity of materials with which they are combined 2 Mostly used with plastics especially PVC, but may be used with concrete and clays. 3 Mostly phthalate esters used in PVC (about 90% of world use. Improve flexibility and durability.

Ester plasticisers  Plasticisers used in PVC and other plastics are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. These compounds are selected on the basis of many criteria including low toxicity, compatibility with the host material, non-volatility, and expense. Phthalate esters of straight-chain and branched-chain alkyl alcohols meet these specifications and are common plasticizers. Ortho-phthalate esters have traditionally been the most dominant plasticizers, but regulatory concerns have led to pressure to change to non-phthalate plasticizers, especially in Europe.esters

Health concerns  Many plasticisers have led to concerns about their toxicity, especially to the hormone producing organs in the body.  Phthalate plasticisers are now being replaced by bio-based plasticisers which are thought to be less toxic.

Reduce, Re-use, Recycle  Why 1. Responsable for large amounts of litter pollution as they are mostly non- biodegradable 2. Use up important finite resources such as fossil fuels 3. Production and use have environmental and health implications.

Health effects  Additives to plastics to improve their performance or desirability carry negative health impacts.  Additives such as cadmium mercury and lead are directly toxic when they leach from the plastic  The plasticiser DEHP is carcinogenic  Endocrine disruption leading to birth defects

Migration. 1. Chemcial additives migrate from plastic packaging into foods because of lack of true chemical bonding. 2. Plastics contaminating food have been reported including Styrene from polystyrene, plasticizers from PVC, antioxidants from polyethylene, and Acetaldehyde from PET For more information: health-effects-of-plastics/ health-effects-of-plastics/

Important links for revision  Types of plastics and their uses GCSE Bitesize:  /materialsandcomponentsrev3.shtml /materialsandcomponentsrev3.shtml  The 7 most common types of plastics  common-plastics-and-how-they-are-typically-used.htm common-plastics-and-how-they-are-typically-used.htm  How stuff works: plastics   Types of plastics: plastichttp:// plastic  warren.org/GCSERevision/resistantmaterials/plastics.html warren.org/GCSERevision/resistantmaterials/plastics.html

Task: 1. You are to produce a poster of six articles. 2. Each poster must be between 1 and 2 pages with at least one page of writing in 14 point. 3. Posters are to be submitted on Wednesday 30th April This means each of you should spend 5 hours homework time on your article.

Articles 1-3 (10 points per article) 1 Plastic Choose 1 plastic, describe its chemistry, manufacture, and links its uses to its properties 2 Dangers of plastics Identify the health issues surrounding a series of plastics. Explain how they are used and why this poses a threat to health. Suggest alternatives and guidelines. 3 Bioplastics Describe and example of a fermented and genetically engineered bioplastic. Describe the industrial processes for production and the uses and benefits.

Articles 4 – 6 (10 points per article) 4 Natural polymers Choose one natural polymer. Describe its role in the living world. Describe its chemistry, how it is created and whether it has any uses for man. 5 Protein synthesis Describe the key stages of protein synthesis. 6 Synthetic polymers Research one synthetic polymer which is not a plastic and describe its chemistry, production and uses plus the properties that make it useful.