1. Polymerisation Flashcards
Name some natural polymers
Wool, cotton, wood and rubber
What is monomer?
A small molecule. Many monomer molecules can be joined together to form a long chain of repeating unites called a polymer.
What is a polymer?
A large molecule consisting of a large number of identical small molecules (monomers).
Name some examples of polymers
Plastics, rubbers, starch, cellulose and protein
Define polymerization
Process by which monomers are converted to polymers
Why is ethene used more extensively in industry than ethane?
Ethene is more reactive due to double bond.
Why are synthetic polymers replacing natural polymers?
- Cheaper
- Better suited to particular function as chemist can produce polymers suitable to specifications.
What is LDPE and HDPE respectively?
Low and High Density Polyethylene
What type of monomers are involved in addition polymerisation?
Double bonded monomers.
What are the two processes to make polyethylene?
- Initiator: Heating for LDPE
- Surface catalyst: Ziegler Natta 1950 for HDPE
What are the requirements for producing LDPE?
- Heat at 300 degrees celsius
- Initiator such as peroxide or oxygen
- High pressure of 1000- 3000atm
What are the consequences for producing LDPE using an initiator?
- It has branched chains and can be easily deformed.
Define free radical
A species with an unpaired outer shell electron
What is the free radical’s role in the formation of a polymer?
- Free radical is reactive
- Radical free ethene molecules can readily join together.
What happens during intiation?
- Initiator (Benzoyl peroxide) molecule is heated to form peroxide free radicals.
What happens during activation?
- Free radicals combine with some monomers.
- Monomers become activated.
What happens during Propagation?
- Activated monomers react with more ethylene monomers to increase its chain length.
- Some branching occurs as chain growth- the radical end often curl on existing chain and removes hydrogen atom.
What happens during Termination?
Process of chain growth terminates as free radicals combine to form a non- activated species.
What else can cause Termination?
Inhibitors, lowering pressure and temperature.
Define a Dimer
A molecule with same functional group at the ends.
What is used in the production of HDPE?
Chronimium oxide.
What gives HDPE extra strength?
Varying pressure can cause cross linking between polymer chains which adds strength.
How is the Zieglar Natta method carried out?
- Ethylene gas is passed through a liquid alkane solution (at 60 degrees celsius) at 1 atm.
- With tiny amounts of catalyst, titanium chloride and triethyl aluminium chloride.
What is the Zieglar Natta catalyst?
Titanium chloride and triethyl aluminium chloride
What is the effect of cross- linked polymer chains?
- Enhances rigidity
- Melting point enhances
Why is it important to measure the temperature of the reaction during the production of polyethylene?
- Heat could make polyethylene decompose as it forms, thus decreasing yield.
How many monomer units does polyvinyl chloride (PVC) have?
400 - 4000
What’s the systematic and common name for PVC monomers?
Systematic: Chloroethene.
Common: Vinyl Chloride
Plastiser + PVC?
Decreases dispersion forces. Polymer becomes more flexible.
UV absorber + PVC?
Prevents UV decomposition of plastic.
Heat stabiliser + PVC?
Decomposes above 80C.
- Adding heat stabilizer would improve its resistance to heat decomposition.
What are addition polymers?
Polymers that can be formed from an addition reaction involving many molecules of one or more monomers in double bonds.
Describe the effect of the Zieglar Natta catalyst.
- Allows process to be carried out at lower temperatures
- Effect the arrangements of units attached to main chain and thus effects density and stability to heat.
What is the common and systematic monomer name for Polystyrene?
Common: Styrene (Vinyl Benzene)
Systematic: Ethenylbenzene
Which polymerisation process is used to make polyethylene?
Addition polymerisation
(Polymerisation using an initiaitor)
Why is HDPE rigid and hard?
HDPE has less branching which allows the polymers to be arranged orderly on top of each other. This crystallines the HDPE and thus, has a white or transcluscent colour.
Why is LDPE flexible?
The initiation polymerisation produces a lot of branching in its LDPEs. This branching prevents orderly arrangements of polymers which allows space for light to seep through or can be easily separated.
