© www.CHEMSHEETS.co.uk 15-Jul-12 Chemsheets A2 025

Addition polymerisation

• Addition polymerisation = reaction where many small molecules (monomers) join together to make a long chain

molecule and nothing else.

• Addition polymers are usually formed by alkenes undergoing addition reactions with themselves.

• Some common examples include:

ethene

C C

H

H

H

H

→

phenylethene

C C

H

H

C6H5

H

→

methyl 2-propenoate

C C

H

H

CH3

COOCH3

→

methyl 2-cyanopropenoate

C C

H

H

CN

COOCH3

→

chloroethene

→

tetrafluoroethene

→

propene

→

• Catalysts are used for the polymerisation, and the exact mechanism depends on the catalyst and alkene (it is not

electrophilic addition – it is usually catalytic addition).

• Polyalkenes are inert (although can burn) – this is partly due to the absence of any polar bonds.

• As they are inert, they are non-biodegradable.

© www.CHEMSHEETS.co.uk 15-Jul-12 Chemsheets A2 025

Condensation polymerisation

• Condensation polymerisation = reaction where many small molecules (monomers) join together to make a long

chain molecule with a small molecule (often water) also formed.

• Many natural polymers are condensation polymers, e.g. silk, starch and DNA.

• The two main types are polyesters and polyamides.

Polyesters

• Esters are formed on reaction between carboxylic acids and alcohols.

• Polyesters are formed when dicarboxylic acids react with diols.

OHHOC OH

O

C

O

HOHO OHC

O

HO C OH

O

ethane-1,2-diol

strong acid orspecific enzyme

• Terylene (PET) is a good example of a polyester, made as shown below:

C

O

HO

O

OHC HO CH2 CH2 OHn + n

benzene-1,4-dicarboxylic acid ethane-1,2-diol

strong acid orspecific enzyme

• Polyesters are hydrolysed (in the presence of strong acid or a specific enzyme) into their constituent acid and alcohol, so they are bio-degradable. The ester linkage (which is polar) is broken.

© www.CHEMSHEETS.co.uk 15-Jul-12 Chemsheets A2 025

Polyamides

• Amides are formed on reaction between carboxylic acids and amines.

• Polyamides are formed when dicarboxylic acids react with diamines.

• Polyamides are hydrolysed (in the presence of strong acid or a specific enzyme), so they are bio-degradable. The amide linkage (which is polar) is broken.

e.g. nylon-6,6 is a good example of a polyamide, made as shown below:

H2N (CH2)6 NH2n + n

hexanedioic acid hexane-1,6-diamine

strong acid orspecific enzyme

C

O

HO (CH2)4 C OH

O

e.g. Kevlar (used in bullet-proof vests) is a another good example of a polyamide, made as shown below:

NH2H2N C

O

HO C

O

OHn n

benzene-1,4-diamine benzene-1,4-dicarboxylic acid

• Polyamides are also formed when amino acids react with each other.

• Nylon-6 is made from the polymerisation of the amino acid 6-aminohexanoic acid.

strong acid orspecific enzyme

NH2 (CH2)5 C

O

OHn