Polymers Flashcards
Polymers
Covalent molecular substances composed of many small molecules joined together, Naming: Poly[monomer]
Monomers
Small molecules, joined together by a polymerisation reaction
Types of polymers
Many found in nature (biodegradable), E.g- carbohydrates, proteins, cotton, spider silk, latex, Synthetic, E.g- polyesters, nylon, Teflon, polythene, PET
Structural properties of polymers
Determined primarily by the type of monomer used, factors: length, branching, cross-linking
How chain length affects polymers
As chain length increases, strength of dispersion forces increases, increasing melting and boiling point, Increased dispersion forces makes the polymer harder and more rigid
How branching affects polymers
Occurs when some monomers react with sites on the side of the polymer chain instead of the polymer chain, Causes polymers chains to be further apart, decreasing the strength of the intermolecular forces which decreases melting and boiling point as well as density but increases flexibility, High density polyethene has up to 95% crystalline regions, Low density polyethene has as low as 65% crystalline regions
How cross-linking affects polymers
When polymer branches are covalently bonded to neighbouring polymer chains meaning it can’t be reshaped due to the strong covalent bonds
Thermoplastic
When there are no cross-links, can be heated and reshaped/recycled
Thermoset plastic
Can’t be turned into a liquid and moulded, decompose or burn when heated, can’t be recycled
Elastomers
when only occasional cross-links are present, chains can move past each other when stretched but cross-links return once force is released, E.g rubber bands, stockings, car tyres
Addition polymerisation
Monomer is unsaturated (contains a double or triple bond), Requires a catalyst to initiate the reaction, Double or triple bond is broken (opens molecule) and single bonds are formed between the monomers
Condensation polymerisation
Two monomers which have functional groups on each end of the monomer, Water is eliminated, Repeating unit- comes from both reactants, E.g- polyesters, polyamides, silicones
Polyesters
Typically formed by combining a dicarboxylic acid monomer with a diol monomer in a condensation polymerisation reaction, Produces water molecules
Polyethylene terephthalate (PET)
Monomers- ethane-1,2 diol and benzene-1,4-dicarboxylic acid, Used in: Fabrics, Recyclable drink bottles, Food packaging
Polyamides
Typically formed by combining a dicarboxylic acid monomer with a diamine monomer in a condensation polymerisation reaction, Produces water molecules
Nylon
Easily drawn into fibres with high tensile strength, Used to make strong, lightweight materials for clothes, parachutes, ropes, fishing line and guitar strings, Can also make hard, rigid plastics that can be used pipe
Silicones
Have an alternative backbone of silicon and oxygen with organic groups attached to each silicon atom, Considered inorganic polymers as there is no carbon in the backbone, Made by condensation polymerisation, Can be oils, greases or rubbery solids, Repels water and water-based products so is used in lubricants, waterproofing, furniture and car polishes, Also used in medical implants
Advantages of polymers
Can be designed for improved physical and chemical properties, Developing biodegradable and recyclable polymers
Copolymers
Polymer made from at least two different monomers, Both addition and condensation polymers
Crystallinity
Materials made from polymers consisting of many long chains that twist around each other, with intermolecular forces from one chain to another, Many polymeric materials contain both crystalline regions and amorphous regions, Percentage of the polymer that is crystalline affects the properties (not percentage of amorphous)
Crystalline regions
closely packed and have stronger intermolecular forces which prevents transmission of light and appears cloudy
Amorphous regions
randomly tangled and unable to pack close together meaning they are less rigid, weaker and often more transparent
Additives
Used to improve or extend the properties of the polymers, Include pigments and UV stabilisers, flame retardants and plasticisers
Plasticisers
Small molecules added to polymers during manufacture, Forces polymers slightly further apart, weaking intermolecular forces making the material softer and more flexible
Foamed polymers
Formed by blowing gas through melted polymer material, Eg. Polystyrene foam- produced by introducing pentane into melted polystyrene beads which causes them to swell up to produce the lightweight, insulating, shock-absorbing foam used for packing material
Environmental impact of polymers
Many polymers are derived from petroleum which is non-renewable and thus increases the environmental impact associated with their production, Plastics are durable, chemically resistant and lightweight however this means they biodegrade very slowly, Waste plastics persist for a long time and low density means they take up a lot of room in land fill and burning releases toxic products
Two ways of recycling
Reprocessing- involves shredding, melting and reshaping used plastic into clean products (can only be used by thermoplastics)
Depolymerisation- involves breaking the polymer back into monomers usually by heating, requires a large amount of energy and has a low yield making it less economically viable than reprocessing
