Polymers
Section: 11. Organic Chemistry | Syllabus: Cambridge AS Level Physics 9702
Polymers Polymers are large molecules made up of many small repeating units called monomers joined together in long chains. They are found naturally and can also be made synthetically. Polymer A large molecule made up of many small repeating units (monomers) joined together by covalent bonds.
Monomer A small molecule that can join with many other similar molecules to form a polymer. Image Placeholder [DIAGRAM: Simple illustration showing monomer units (small circles) joining together to form a polymer chain (connected circles in a long line).
Label: "Monomers → Polymer"] Polymerization Polymerization The chemical process in which monomer molecules join together to form a polymer chain. General Equation: n(monomer) → polymer where n = a very large number (could be thousands or millions) Key Concept The prefix "poly-" means "many".
For example, poly(ethene) means "many ethene units joined together". Types of Polymers Natural Polymers Polymers that occur naturally in living organisms: Proteins - made from amino acid monomers (e.g., enzymes, hair, silk) Starch - made from glucose monomers (energy storage in plants) Cellulose - made from glucose monomers (plant cell walls) DNA - made from nucleotide monomers (genetic information) Natural rubber - made from isoprene monomers (latex from rubber trees) Wool - protein polymer from sheep hair Cotton - cellulose polymer from cotton plants Image Placeholder [INTERACTIVE: Gallery of natural polymers showing images of: DNA double helix, starch granules, cellulose fibers, silk thread, natural rubber, wool, cotton.
Each with chemical structure diagram.] Synthetic (Man-made) Polymers Polymers manufactured by humans from simple chemicals: Poly(ethene) / Polythene - plastic bags, bottles (from ethene) Poly(propene) / Polypropylene - ropes, crates, carpets (from propene) Poly(chloroethene) / PVC - pipes, window frames (from chloroethene) Poly(styrene) / Polystyrene - packaging, insulation (from styrene) Nylon - clothing, ropes, parachutes (from diamine + dicarboxylic acid) Polyester - clothing, bottles (from diol + dicarboxylic acid) PTFE (Teflon) - non-stick coatings (from tetrafluoroethene) Diagram Placeholder [TABLE/CHART: Visual comparison showing common synthetic polymers with their monomers, structures, and everyday uses with product images] Properties of Polymers Physical Properties High molecular mass - very large molecules (10,000 to millions) Do not conduct electricity - covalent bonding, no free electrons Strong and durable - long chains give strength Insoluble in water - non-polar (most synthetic polymers) Low density - lighter than metals and ceramics Do not corrode - resistant to chemicals and weathering Can be flexible or rigid - depends on structure and cross-linking Variable melting points - some melt when heated (thermoplastics), others don't (thermosets) Chemical Properties Unreactive - stable, don't easily break down chemically Resistant to acids and alkalis - useful for containers and pipes Can burn - most polymers are flammable and produce toxic fumes Non-biodegradable - most synthetic polymers don't decompose naturally (environmental issue) Interactive Placeholder [INTERACTIVE: Property comparison tool - slide bars to compare different polymer properties (strength, flexibility, heat resistance, chemical resistance) for common polymers like polythene, PVC, nylon, etc.] Structure and Properties Relationship Chain Length Longer chains → stronger polymers, higher melting point Shorter chains → weaker, lower melting point Reason: More intermolecular forces between longer chains Branching Unbranched (linear) chains → can pack closely together, stronger, higher density Branched chains → can't pack well, weaker, lower density, more flexible Example: High-density poly(ethene) (HDPE) vs Low-density poly(ethene) (LDPE) Diagram Placeholder [DIAGRAM: Two side-by-side illustrations comparing: Left: Linear polymer chains packed tightly together (HDPE) Right: Branched polymer chains with gaps between them (LDPE) Show how packing affects density and properties] Cross-linking Cross-links - covalent bonds between different polymer chains More cross-links → harder, more rigid, higher melting point Few cross-links → more flexible No cross-links → chains can slide past each other Image Placeholder [DIAGRAM: Illustration showing polymer chains with cross-links (bonds connecting different chains) creating a 3D network structure] Common Synthetic Polymers Poly(ethene) - Polythene Monomer: Ethene (CH₂=CH₂) Structure: H H | | -( C - C )- | | n H H Types: LDPE (Low-Density Polyethene): Branched chains, flexible, plastic bags, squeeze bottles HDPE (High-Density Polyethene): Linear chains, rigid, milk bottles, pipes, buckets Poly(propene) - Polypropylene Monomer: Propene (CH₃CH=CH₂) Uses: Ropes, carpets, crates, clothing, thermal underwear Properties: Strong, flexible, high melting point, resistant to chemicals Poly(chloroethene) - PVC (Polyvinyl Chloride) Monomer: Chloroethene/vi…
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