3.4.3 addition polymers

polymer

a large, long-chain molecule formed from many small molecules joined together

monomer

small molecules that join to make polymers

addition polymer

• large molecules made up of smaller molecules called monomers

  • e.g. alkanes formed from alkenes and substituted alkenes.

• no other products formed

what is addition polymerisation?

what is the monomer?

• the formation of large, long-chain molecules from lots of small molecules joining together with no other products formed.

• monomer: alkenes (from crude oil).

how does addition polymerisation occur?

• conditions:

  • high temperature

  • high pressure

  • a catalyst or initiator like O₂

• to form the polymer, the double bond in the alkenes open up and joins one monomer to another

what type of addition polymers are formed from higher pressures and temperatures?

• branched chain polymers with weak van der Waals forces

• LDPE, low density as the branched molecules cannot pack as closely together

  • less surface contact

what type of addition polymers are formed from lower pressures and temperatures?

• straight chain polymers with strong van der Waals forces

• HDPE, high density as the straight molecules can pack closely together

  • more surface contact

how are addition polymers named?

give examples of addition polymers

• they are named using ‘poly(name of alkene monomer)’.

• e.g. LDPE, HDPE, both formed from the monomer ethene.

repeating unit of addition polymers

shows the arrangement of atoms that are repeated in the polymer chain

• bonds must extend outside the brackets

how many repeating units are present in this polymer?

n = 7

choose the correct option:

E-Z isomers of an alkene form polymers with the same / different repeating unit(s).

the same

what happens at the ends of an additon polymer?

• C atoms at the ends only have 3 bonds.

• during polymerisation, other molecules are added to cap the ends of the polymer chain.

why do polymers have higher melting points than their monomers?

• polymers are larger molecules/longer-chain molecules

• so have more electrons

• so have stronger van der Waals forces between molecules

compare the reaction conditions for making LDPE and HDPE.

• LDPE high temp, HDPE low temp.

• LDPE high pressure, HDPE low pressure.

• LDPE oxygen is needed, HDPE ziegler-natta catalyst is needed and the alkenes / chains bond to the catalyst’s surface (heterogeneous catalyst)

compare the properties of LDPE and HDPE.

• in LDPE molecules are loosely packed due to branching.

• in HPDE molecules are tighly packed.

• LDPE is flexible and soft.

• HDPE is stiff/rigid and hard.

compare the uses of LDPE and HDPE.

• LDPE is used in plastic bags and cling film.

• HDPE is used in plastic bottles and buckets.

what is PVC?

poly(chloroethene)

what are plasticisers and what is their role?

• small molecules added in between polymer chains.

• cause chains to move further apart.

• so weaken the intermolecular forces between chains.

• so chains can move over each other.

• so polymer becomes more flexible (/less brittle).

example of the use of plasticisers

• using plasticisers makes PVC more flexible and softer

  • also makes PVC waterproof.

.

• PVC is rigid, and the chains are attracted to each other by van der Waals forces and dipole-dipole forces.

• using plasticers weakens these intermolecular forces.

• flexible PVC is relatively soft.

rigid PVC must be used to make:

• plastic pipes

• window frames

flexible PVC must be used to make:

• flooring

• electrical insulation in cables

• clothing

a use of poly(propene)

used to make carpets

what is polystyrene?

what is polystyrene used for?

what is the side group in the monomer of polystyrene?

• poly(phenylethene).

• used to make foam food containers and drinks cups.

• the side group in phenylethene is benzene.

define non-biodegradable

not broken down by microorganisms in the environment

why are addition polymers unreactive?

• they contain many C-C and C-H bonds.

• these bonds are non-polar and (relatively) strong, so are difficult to break.

what is an advantage of the lack of reactivity of addition polymers?

• their lack of reactivity makes them useful molecules, e.g. they can be used for containers for food and drinks without the polymer reacting with the contents.

what are a disadvantage of the lack of reactivity of addition polymers?

• their lack of reactivity makes them non-biodegradable.

• this means they can pollute the environment for decades or longer.

• this is harmful to wildlife, e.g. seabirds can become tangled in polymer waste or consume it, which can be fatal.