POLYMERS
Polymers
What is a polymer?
Very Large molecules structures chain-like in nature. Poly mer many repeat unit
repeat repeat repeat unit unit unit H H H H H H H H H H H H H H H H H H
C C C C C C C C C C C C C C C C C C H H H H H H H Cl H Cl H Cl H CH3H CH3H CH3 Polyethylene (PE) Polyvinyl chloride (PVC) Polypropylene (PP) Bulk or Commodity Polymers
Polymers - What are they?
• Polymers are a special kind of macromolecule
• The word polymer comes from the Greek words “poly,” meaning “many”, and “meres,” meaning “parts” or “repeating units”
• A Polymer consists of a large chain of repeating molecules (monomers) that are attached in an end to end fashion
Description of Polymers
•Imagine a string of beads • Each bead is identical (for example, red sphere) • Represents the “mer” • The string can contain 100’s of beads • Represents the “poly” characteristic • The string in between the beads represents the chemical bond between monomers
Length of Polymers • Polymer chains are HUGE! • Polymers typically consist of between 20,000 and 40,000 individual monomers • If each bead on the string of beads were one inch apart, one polymer molecule could be as long as 10 football fields!!!
• This chain length is what gives the polymer most of its desirable characteristics
Description of Polymers
• Polymer chains are flexible, and usually “clump” together into a smaller shape
• This enables the individual chains to interact and become entangled
• This helps to give a polymer its strength and flexibility Chemistry of Polymers
Note: polyethylene is just a long HC
- paraffin is short polyethylene Types of Polymers
•There are two main types of polymers
• Natural • (cotton, silk, wood, leather…)
• Synthetic • (plastics, nylon, latex…) Synthetic Polymers
•There are two basic types of synthetic polymers • Thermoplastics (plastics, Styrofoam) • These can be softened by heating and hardened by cooling - easily recycled • Can easily be cast into various shapes • Thermosets (epoxy’s, adhesives) • These harden after being heated • Can easily be cast into different shapes • Cannot be reformed
Polymers - Pros and Cons
• A polymer has many very advantageous properties. Polymers are: • Lightweight • Strong and durable • Cheap • Easy to manufacture
• Unfortunately, polymers do not easily biodegrade and end up producing large amounts of waste
Uses of Polymers
• Polymers are incorporated into nearly every aspect of daily life • Entertainment • Sports • Clothes • Hobbies/Toys • Household products • Automotive Range of Polymers
§Traditionally, the industry has produced two main types of synthetic polymer – plastics and rubbers.
§Plastics are (generally) rigid materials at service temperatures
§Rubbers are flexible, low modulus materials which exhibit long-range elasticity. Range of Polymers
§Plastics are further subdivided into thermoplastics and thermosets Range of Polymers
Range of Polymers
§Another way of classifying polymers is in terms of their form or function Common thermoplastics
• Low Density Polyethylene. Branch chain polymer produces weak, soft and flexible polymer. The most common polymer. Used for buckets, bags, electrical cable, cups, etc.
• High Density Polyethylene. Linear chain polymer which is stiff, strong and resists chemicals. Used for bottle crates, barrels and plumbing joints.
• Polypropylene. Tough and rigid polymer with high impact strength. Used for chairs, helmets, hinged boxes and toys.
• Polystrene. Brittle in solid form and is used for jugs, egg boxes, jar tops. Expanded or foamed polystyrene is soft, low density and a heat insulator and used for coffee cups, packaging and house insulation.
• Polyvinyl Chloride. Rigid PVC is used for gutters and doors. The plasticised version is more flexible and used for coats, suitcases, hose pipes, etc.
• Acrylic. PMMA can be transparent or opaque and is brittle but machines well. It is used for car lights, shop signs, safety glasses, etc.
• Nylon. Produced by condensation polymerisation, Nylon is hard wearing and resistant to chemicals. Used for clothing, nets, ropes, gears. Thermosetting plastics
• Will only mould once.
• Strong primary bonds are connected by strong covalent bonds.
• Cross-link process (curing) formed by heat and pressure.
• Non-reversible structure cannot be softened by heating. • Phenol formaldehyde. Hard and brittle, ‘Bakelite’ has been used for electrical fittings and saucepan handles.
• Urea formaldehyde. Good electrical and thermal properties and used for electrical fittings and door handles. Elastomers
• Produced by addition polymerisation.
• Long chain structure, which is coiled, giving elastic properties.
• Natural rubber is produced from trees. It can be vulcanised (cross-linked) by adding sulphur.
• Synthetic rubbers are manufactured with a range of properties, eg ‘neoprene’.
• Glass transition temperature below room temp. changes from flexible to rigid solid.