Polymers

Question 1

How do you identify the repeating unit of an addition polymer from its monomer?

How do you identify the monomer of an addition polymer from its repeating unit?

(TBAT draw the above)

Answer 1

Addition polymers are made from monomers with a C=C double bond. The double bond opens and the monomers bond together to form a backbone of carbon atoms upon polymerisation.

Addition polymerisation is a free-radical addition reaction.

• Repeating units; open up double bond, add some square brackets and a subscript ‘_n’ outside of the brackets.
• Monomers; add double bond to repeating unit.

Question 2

How are condensation polymers formed?

Answer 2

Condensation polymers are formed by reactions between:

• dicarboxylic acids and diols (polyesters)
• dicarboxylic acids and diamines (polyamides)
• and between amino acids.

Condensation polymers are normally made from two different monomers; each with two functional groups; each funcitonal group reacts with a group on another monomer to form a peptide link, creating polymer chains. A water molecule is lost each time a link is formed.

Question 3

What is the linkage of a polyester?

Answer 3

Dicarboxylic acids and diols (polyesters)

Polyester has the ester linkage –COO– repeated.

Diol: HO–A–OH
(double ended alcohol)
Dicarboxylic acid: HOOC–B–COOH
(double ended carboxylic acid)

Upon polyester formation, the diol loses a H from its –OH group whilst the dicarboxylic acid loses the –OH from its carboxyl groups, forming ester links. H₂O is given out.

Question 4

What is the linkage of a polyamide?

Answer 4

Dicarboxylic acids and amines (polyamides)

Polyamides have the amide linkage –CONH– repeated.

Diamine: H₂N–A–NH₂
(double ended amine group)
Dicarboxylic acid: HOOC–B–COOH
(double ended carboxylic acid)

Upon polyamide formation, the diamine loses a –H from its –NH2 group whilst the dicarboxylic acids loses the –OH from its carboxyl groups, forming amide links.
H₂O is eliminated.

Question 5

Are addition polymers (polyalkenes) biodegradable?

Answer 5

• Addion polymers; polyalkenes, are not biodegradable as they are chemically inert; essentially long-chain alkane molecules.
• Only strong, non-polar C-H and C-C bonds are present; these is nothing in the natural environment that naturally break them down.
• Usually disposed of in landfill sites along with other rubbish, or by incineration.
• Some are melted down and remoulded.
• Polyalkenes may be burnt to carbon dioxide and water to produce energy, but poisonous carbon monoxide may be released if combustion is incomplete.
• Does not add to problem of increasing CO₂ in the atmosphere.

Question 6

Are condensation polymers such as polyester and polyamide biodegradable?

Answer 6

• Yes; they can be broken down by hydrolysis; biodegradable with the reverse of the polymerisation reaction to which they were formed.
• However, the process is very slow.

Question 7

What are the advantages and disadvantages of recycling polymers (plastics)?

Answer 7

Advantages:

• Almost all plastics are derived from crude oil; recycling saves this expensive and non-renewable source, as well as saving on energy that would be used in refining it.
• If plastics are not recycled, most end up in landfill sites.

Disadvantages:

• The plastics need to be collected, transported and sorted, which uses energy and manpower; thus it is expensive.

Question 8

What are the advantages and disadvantages of some different methods of disposal of polymers?

Answer 8

Burying; landfill:

• *Advantages**: cheap and easy.
• *Disadvantages**: requires areas of land, waste decomposes and releases methane (a greenhouse gas), leaks from landfill sites can contaminate water supplies.

Burning; combustion:

• *Advantages**: heat generated from combustion can be used to generate electricity.
• *Disadvantages**: process needs to be carefully controlled; toxic gas emission e.g. PVC contains chlorine, produces HCl when burned. Toxic gases are thus passed through scrubbers to neutralise HCl etc. by reaciton with a base, but still contributes CO₂ to greenhouse effect.

Question 9

Explain why polyalkens are chemically inert.

Answer 9

As thye have a backbone akin to a saturated alkane; non-polar, unreactive, unless there is UV light to break the bonds in the molecules.

Question 10

Explain why polyesters and polyamides are biodegradable.

Answer 10

Their amide/ester linkage can be hydrolysed under acidic (HCl) conditions or via enzyme action.