WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:06.767 Unit S C 24: Polymers. 00:00:09.433 --> 00:00:16.312 A polymer is a substance made from many repeating units linked together, giving a high average relative molecular mass. 00:00:16.462 --> 00:00:20.392 A monomer is a small molecule that can join into a polymer chain. 00:00:23.067 --> 00:00:28.409 In addition polymerisation, monomers containing C double bonded to C add together. 00:00:28.559 --> 00:00:34.669 The double bond opens to form single bonds linking a chain; no small-molecule by-product is lost. 00:00:37.333 --> 00:00:39.467 Ethene forms poly(ethene). 00:00:39.617 --> 00:00:42.582 Draw a repeat unit with a single C to C bond, 00:00:42.732 --> 00:00:44.844 two hydrogens on each carbon, 00:00:44.994 --> 00:00:47.597 continuation bonds crossing brackets, 00:00:47.747 --> 00:00:49.752 and n outside the brackets; 00:00:49.902 --> 00:00:52.398 the bracketed unit is part of a chain, 00:00:52.548 --> 00:00:55.011 not an isolated ethane molecule. 00:00:55.161 --> 00:01:00.036 Continuation bonds cross the brackets; n represents many repeating units. 00:01:04.700 --> 00:01:10.299 Propene forms poly(propene), with a C H 3 side group on alternate backbone carbons. 00:01:10.449 --> 00:01:20.621 Chloroethene forms poly(chloroethene), PVC, with a chlorine side group; tetrafluoroethene forms PTFE, with fluorine atoms replacing the hydrogens. 00:01:23.300 --> 00:01:33.069 To obtain an addition monomer from a repeat unit, identify the two backbone carbons and restore the C double bonded to C bond between them, keeping their side groups. 00:01:33.219 --> 00:01:39.521 To obtain the repeat unit from a monomer, open C double bonded to C and draw chain continuation bonds. 00:01:42.200 --> 00:01:49.591 Polymer molecules have different chain lengths, so their relative molecular masses form a distribution and are described with an average. 00:01:49.741 --> 00:01:54.017 Longer chains and chain interactions can affect material properties. 00:01:56.667 --> 00:02:00.977 Different monomers and processing produce polymers with different properties. 00:02:01.127 --> 00:02:05.701 Polymer does not mean a single material with one melting behaviour or strength. 00:02:08.367 --> 00:02:16.183 Poly(ethene) can be flexible and water-resistant, useful for bags, packaging and bottles; grades differ in stiffness and density. 00:02:18.833 --> 00:02:24.475 Poly(propene) is tough and light, useful for containers, fibres and some reusable hinges. 00:02:24.625 --> 00:02:29.573 Select it from property data rather than assuming all plastics are interchangeable. 00:02:32.233 --> 00:02:38.728 PVC can be rigid for pipes or window frames, or made flexible with plasticisers for cable insulation. 00:02:38.878 --> 00:02:43.956 Its electrical insulation and durability are useful, but disposal requires care. 00:02:46.633 --> 00:02:53.469 PTFE is chemically resistant, slippery and heat-resistant for many uses, including non-stick coatings. 00:02:53.619 --> 00:02:57.276 It is not an excuse to ignore manufacturer temperature limits. 00:02:59.933 --> 00:03:09.857 Compare polymer properties with the demands of a product: flexibility, toughness, density, electrical insulation, chemical resistance, heat resistance and cost. 00:03:10.007 --> 00:03:14.138 A useful property in one setting can be a disadvantage in another. 00:03:16.800 --> 00:03:24.350 (Higher tier) A polyester can form when a molecule with two carboxylic-acid groups reacts with a molecule with two alcohol groups. 00:03:24.500 --> 00:03:29.022 Two functional groups on each monomer allow growth in both directions. 00:03:31.700 --> 00:03:38.462 (Higher tier) A carboxylic-acid group reacts with an alcohol group to form an ester link, releasing a water molecule. 00:03:38.612 --> 00:03:43.114 Repeating this forms a polyester by condensation polymerisation. 00:03:43.264 --> 00:03:48.574 Unlike addition polymerisation, a small molecule is released when each link forms. 00:03:48.724 --> 00:03:53.167 A diacid and a diol can form many ester links along a polyester chain. 00:03:57.833 --> 00:04:03.965 (Higher tier) The ester link contains carbon double bonded to oxygen and single bonded to oxygen. 00:04:04.115 --> 00:04:12.092 Draw both carbonyl and single-bonded oxygens; the water comes from an O H of the acid and a hydrogen from the alcohol group. 00:04:14.767 --> 00:04:19.041 (Higher tier) Each monomer with two functional groups can join at both ends. 00:04:19.191 --> 00:04:27.466 If k such molecules join to make one straight chain with no rings, they form k minus 1 links and release k minus 1 water molecules. 00:04:27.616 --> 00:04:32.310 Repeat-unit drawings show the repeating pattern rather than the chain’s end groups. 00:04:34.967 --> 00:04:40.426 D N A is a natural polymer of nucleotides; four different nucleotide types are used. 00:04:40.576 --> 00:04:45.482 Starch is based on sugar monomers, while proteins are polymers of amino acids. 00:04:48.133 --> 00:04:53.507 Natural and synthetic polymers can have very different biodegradability and properties. 00:04:53.657 --> 00:04:58.384 Being a polymer alone does not establish whether a material will persist in landfill. 00:05:01.067 --> 00:05:08.243 Many conventional synthetic polymers are not readily biodegradable and can persist in landfill or the environment. 00:05:08.393 --> 00:05:14.600 Litter and fragmented plastic can affect wildlife; landfill persistence is separate from toxicity. 00:05:17.267 --> 00:05:21.221 Making polymers often uses finite petrochemical resources. 00:05:21.371 --> 00:05:28.623 Recycling can reduce demand for new feedstock, but collection, sorting, cleaning and processing require energy and money. 00:05:31.300 --> 00:05:38.701 Different polymers must usually be separated before melting and reforming, because mixed materials can produce poor-quality products. 00:05:38.851 --> 00:05:42.387 Contamination and additives can complicate recycling. 00:05:45.067 --> 00:05:53.597 Burning polymers can recover energy but produces carbon dioxide and may release harmful gases depending on composition and conditions; 00:05:53.747 --> 00:05:57.231 chlorine-containing polymers can produce acidic gases. 00:05:57.381 --> 00:05:59.877 Controlled emissions treatment is needed. 00:06:02.533 --> 00:06:08.035 Reuse can avoid repeated manufacture when products are durable and used enough times. 00:06:08.185 --> 00:06:16.030 Compare whole-life data, transport, washing, breakage and disposal rather than assuming reuse always wins for every scenario. 00:06:18.700 --> 00:06:27.691 Choose disposal routes using economic costs, available collection systems, recovered material quality, energy use and environmental effects. 00:06:27.841 --> 00:06:31.909 Recycling rates and theoretical recyclability are different claims. 00:06:34.567 --> 00:06:36.295 That completes Polymers. 00:06:36.445 --> 00:06:39.790 Revisit the notes and test yourself on the revision website.