Polymer Revolution module mind map

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  • Polymer Revolution
    • the start of the revolution
      • most polymers were discovered by accident and their widespread use occurred when crude oil became the main raw material
        • Types of Plastics (polymers that at some point in their manufacture can flow
          • Thermosets: have "cross links" between polymer chains so they char/blacken upon heating
          • Elastomers: have fewer cross links so are soft and springy, can be deformed then go back to their original shape
          • Fibres: strong thermoplastics thatdo not deform, can be made into strong, thin threads that can be woven
    • the polythene story
      • produced accidentally when Gibson and Fawcett reacted ethene and benzaldehyde under a pressure of around 2000 atmospheres. There was a leak in the equipment so oxygen got in and it created a waxy solid (CH2)
        • because the reaction was temperamental and frequently exploded work was stopped. Until 2 years later when Gibson discovered that using cold ethene kept the reaction cool so it didn't explode, they also found that varying pressure altered the rate of reaction
          • Micheal Perrin discovered that without oxygen,polymerisation didn't occur and that too muchoxygen made the reaction go outof control, he also discovered that Benzaldehyde was not needed for the polymerisation reaction
            • Because a polymer is just a very big molecule it should behave as any other alkane of high relative molecular mass (and it does in many ways), but because poly(ethene) is just a mix of slightly varying monomers it does not have a sharp melting point and softens over time (however it softens and melts at the same temperature as a large alkane)
              • the intermolecular forces arise here because the polymer is a straight chain and so the chains fit closely together meaning that more induced dipoles can occur (from instantanious dipoles) and therefore the intermolecular forces are stronger
    • towards high density polymers
      • the polyethene produced by Fawcett and Gibson is now called low density polyethene (LDPE) because although they had some control over the chains they were still branced and so less dense
      • High Density Polyethene (HDPE was made by Karl Ziegler when he was researching the catalytic effects of organometallic compounds
        • he found that passing ethene at atmospheric pressure through a solution of TiCl4 and (C2H5)3Al it caused the immediate production of polyethene with very little branching causing a relative moelular mass of around 3 million (in this form polyethene is said to be crystaline)
          • HDPE is less easily deformed by heat than LDPE and because it can also be sterilised by heat it is useful in hospitals as bedpans and buckets
          • Guilio Natta further developed alkylaluminium catalysts: when he used ziegler's method to polymerise propene he produced a stereoregular isomer (crystaline) and an irregular amorphous form of polyethene. he developed ziegler-Natta catalysts
            • Ziegler-Natta catalysts were then further developed into Metallocenes that allowed the control of molecular mass as well as structure: metallocenes are madde of two flat organic molecules with arene ring systems with a transition metal such a zirconium or titanium sandwiched inbetween
              • Because Metallocenes allow greater control over polymer properties they can be used to make plastics impermeable to air that are very thin and tear resistant and resistant to gamma radiation (making them useful for blood bags)
    • dissolving polymers
      • Poly(ethenol) is a polymer that dissolves in water because of hydrogen bonds: because of the OH group on the polymer it can form hydrogen bonds with the H2O and so dissolves
        • Poly(ethanol) is not made by the polymerisation of ethanol but instead from the ester exchange of Poly(Ethenyl Ethanoate) where it is reacted with methanol, breaking some of the ester groups on the side chains and converting them into OH groups
      • Dissolving polymers have many uses: they are used in washing machine tablets as well as in hospitals as laundry bags meaning that they can dissolve to wash the clothes meaning possibly infected clothes do not have to be handled
    • polymers that outdo nature
      • Poly(tetrafluoroethene) or PTFT (also called teflon) was discovered when Roy Plunkett wanted to use some gaseous tetrafluoroethene however when he opened the cylinder is had polymerised
        • he discovered the non-stick properties of PTFE (it is now used to coat pans) and also its chemical resistant properties.
          • PTFE is also hydrophobic and Bob Gore used this property to develop Gore-tex that is used in clothing: he realised that when stretched PTFE had holes in that would let water vapour out but not let liquid water in. He therefore sandwiched a layer of PTFE and oil-hating polymer together inbetween fabric so that oils from skin and cosmetics cannot block the pores in the PTFE.
      • ETFE is a copolymer of ethene and tetrafluoroethene. It is transparent, lightweight and resistant to radiation
        • Because of this it made the eden project possible as glass was too heavy to be adequatly supported, not resistant to radiation long term and also not shatterproof
      • neoprene was originally used as a rubber substitute but now is used for wetsuits and phone cases. it is an elastomer made from the polymerisation of chloropropene. it is non-porus, resilient to light, heat and chemical attack.
        • Its properties can be modified by copolymerising it with 2,3-dichloro-1,3-butadiene and treating it with sulfur to introduce cross linking making it more rigid
      • Natural rubber is an addition polymer of 2,3-dichloro-1,3-butadiene (also called isoprene. polyisoprene occurs naturally mainly in the Z form (remember E/Z isomerism)
        • a malaysian tree also produces polyisoprene, however, it is in the E formation meaning that unlike in the Z formation it is non-elastic and hard. E polyisoprene has been used to coat golf balls and early underwater cables.
  • how to write out a polymer: in brackets with side bonds going out of them with n at the end representing any number


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