12.3B Synthetic Polymers Flashcards
Addition Reaction
an organic reaction in which two reactant molecules combine to give a single product molecule.
- Addition reaction of the alkenes forms the basis of plastic industry
Cross-link
a bond (covalent or ionic) that links one polymer chain to another.
It is used for promotion of a change in polymers’ physical properties
Monomer
a small, reactive molecule that reacts to make long-chain molecules called polymers
small, reactive molecules that react togther to make polymers
Polymer
a long-chain molecule made up of many repeating units
Polymerisation
The process of joining monomers together to form polymers
- when alkene molecules react, one of the C=C bonds breaks and joins its neighbouring molecule
- there are 2 types of polymerisation:
1) Addition polymerisation
2) Condensation polymerisation
Addition polymerisation
the reaction in which monomers containing carbon-to-carbon double bonds react together to form long-chhained molecules called polymers
- chain reaction, once gets started it s able to keep itself going
Three steps of this reaction:
1) Initiation
2) Propagation
3) Termination
Addition polymerisation: 1. INITIATION
1) A peroxide molecule breaks up into 2 reactive free radicals
Light or heat can provide the energy for this process
ROOR + energy → 2RO●
2) Free radical initiator (RO●) attacks and attaches to a monomer molecule
This forms a new free radical, which is called the activated monomer
RO● + CH2=CH2 → RO—CH2—CH2●
Addition polymerisation: 2. PROPAGATION
- the newly-formed activaied monomer attacks and attaches to the double bond of another molecule
- This addition occurs again&again to make the long polymer chain
RO—CH2—CH2● + nCH2=CH2 → RO-(-CH2=CH2-)n-CH2—CH2●
Addition polymerisation: 3. TERMINATION
- A growing polymer chain joins another free radical
- Peroxide break up to form two radicals, so that two radicals could join to make a stable bond
R● + R’● → R—R’
Low density poly(ethene) LDPE
More BRANCHED structure
Temperature: 200°C
Pressure: about 2000 atm
Initiator: a small amount of oxygen of an organic peroxide
PROPERTIES:
- Quite a lot of branching along the hydrocarbon chain, and thus prevents the chains from lying tidily close to each other
- LDPE is about 3% less dense than HDPE
- waterproof
USES:
-Plastic carrier bags and other similar low strength & flexible sheet materials
High density poly(ethene) HDPE
Temperature: 60°C
Pressure: low a few atm
Initiator: Ziegler- Natta catalysts or other metal compounds
PROPERTIES:
- Has very little branching along the hydrocarbon chains. Van der Waals attractions between the chains are greater and so the plastic is stronger and has a higher melting point
- watreproof
USES:
- Plastic milk bottles and similar containers, washing up bowls, plastic pipes and so on
Poly(propene) PP
Ziegler-Natta and other modern catalysts or high pressure
USES:
- plastic crates & ropes
- road paint
- roofing materials like “roofing felt”
- sealants & adhesivies
- packaging (plastic film for shrink wrapping food)
- medical uses (medical tubing, medical bags & pouches )
Ziegler-Natta catalysts
are a mixture of titanium compounds like TiCl3 and compounds of aluminium like Al(C2H5)3
Poly(chloroethene) PVC
Intermolecular forces present: DIPOLE-DIPOLE INTERACTIONS
PROPERTIES:
- Cheap
- Good insulator
- Flexible
- Pure poly(chloroethene) tends to be hard and rigid because of the presence of additional dipole-dipole interactions due to the polarity of the carbon-chloride bonds
Plasticisers are added to the poly(chloroethene) to reduce the effectiveness of these attractions and make the plastic more flexible and softer, also decrease its viscosity or friction
USES:
- guttering & plumbing pipes
- plastic windows
- electrical cable insulation
- sheet materials for flooring
- footwear & clothing
Poly(tetrafluoroethene) PTFE Teflon or Fluon
PROPERTIES:
- high melting point of 327°C
- slippery
- shiny
- very resistant to chemical attack
- unreactive
The carbon chain is so wrapped up in fluorine atoms that nothing can get at it to react with it
USES:
- non-stick kitchen & garden tools
- low-friction bearings
- waterproof clothing
Polystyrene PS
PROPERTIES:
- hard, solid plastic
- made into a foam material, called expanded polystyrene (more 95% of air)
- strong
- brittle
- strength at low temperature
USES:
- food packaging
- laboratory ware
- home & appliance insulation
- lightweight protective packaging
- surfboards
Polyisopropene
Intermolecular forces present: VAN DER WAALS FORCES
PROPERTIES:
- tensile strength
- elongation
- abrasion resistance of natural rubber(polyisoprene)
is excellent over its working temprature range of approx -50°C to +100°C
Vulcanisation - a process that makes rubber tyres more resilient and hardwearing. This links rubber polymer chains by covalent bonds across sulphur bridges
Q: State differences/advantages of the artificial fibers over the natural ones
poly(propene) over cotton:
- does not decompose/unreactive
- not affected by enzymes
- not attacked by aqueous or polar reagents found in tissues
- does not absorbs water
Q: How some polymers are able to conduct electricity?
Thru its long chain of delocalised electrons/mobile electrons
Have planar geometry, and the pi-bonds/p-orbitals overlap with each other.
Condensation polymerisation
A reaction that joints monomers and also produces small molecules as a condensation product
Condensation polymers are formed from monomers that contain at least two reactive functional groups within their molecules (in same molecule or in two differetn ones)
- Carboxylic acid (-COOH) + Alcohol (-OH) → Polyester + H2O
- Amines (-NH2) + Carboxylic acid (-COOH) → Polyamide + H2O
- Amines (-NH2) + Acyl chlorides (-COCl) → Polyamide + HCl
Copolymer
is a polymer derived from more than one species of monomer
Polyesters
dicarboxylic acid + diol→ polyester + water
Ester linkage —C(=O)—O—
Polyesters: TERYLENE
n HOOC—benzene ring—CO|OH + n H|O—CH2CH2—OH → -[-C(=O)—benzene ring—C(=O)—O—CH2—CH2—O-]-n + (2n-1)H2O
CONDITIONS: catalysts is antimony(lll) oxide, temperature ~ 280°C
PROPERTIES:
- Very strong
- can be flame resistant
- thermoplastic
- does not decompose
- resists most alkalis but can be damaged by acids
- versatile
ADVANTAGES:
+ strong when wet
+ dries quickly
+ crease resistant
+ cheap
+ resists bacteria
DISADVANTAGES:
- poor absorbency so it is difficult to dye
USES:
- bottels for soft drinks (PET)
- (fibre) clothes
- ties
- sewing threads
- medical textiles
- net curtains
- carpets
Polyesters: POLY(LACTIC ACID) PLA
n HO—CH(CH3)—COOH → -[-O—CH(CH3)—C(=O)-]-n + water
Polyamides
Amide link —C(=O up)—N(—H down)—
- Amines (-NH2) + Carboxylic acid (-COOH) → Polyamide + H2O
- Amines (-NH2) + Acyl chlorides (-COCl) → Polyamide + HCl
Polyamides: Nylon 6,6
PROPERTIES:
- very strong and hard-wearing
- does not decompose or rot
- melts as burns
- not very absorbent so dries quickly
- crease resistant
- resists alkalis. but can be damaged by acids
- versatile
ADVANTAGES:
+ strong when wet
+ inexpensive
+ resists bacteria
+ durable & long lasting
DISADVANTAGES:
- sunlight damages it; discolors & makes weak
- low absorbency
- not always comfortable to wear
USES:
- Clothing
- Ropes
-Carpets & rugs
- Seat belts
Polyamides: Kevlar
n HOOC—benzene ring—COOH + n H2N—benzene ring—NH2 → -[-C(=O)—benzene ring—C(=O up)—N(—H down)—benzene ring—N(—H)-]-n + water
Its long, linear polymer chains can line up nex to each other in a regular pattern, resulting in extensive hydrogen bonding between the poplymer chains of Kevlar. (hydrogen bonds hold chains together)
USES:
- bullet-proof vests
- ropes
- fire protection cloting
- modern “leathers”
- tyres
Hydrolysis of Polyesters
- attacked readily by alkalis (ex. NaOH), but much more slowly by dilute acids
- ester linkages are broken
Hydrolysis of Polyamides
- fairly readily attacked by strong acids, but are much more resistant to alkaline hydrolysis
- faster at higher temperatures
- Kevlar is more resistant to hydrolysis than Nylon
Biodegradability
Because of hydrolysis the condensation polymers are biodegradable and constitute a smaller environmental hazard than the addition polymers.
Chains of addition polymers are made up of non-polar C—C bonds which are non-biodegradable
