Polymers (AQA A Level Chemistry): Flashcards
Exam code: 7405
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What is a condensation polymer?
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What is a condensation polymer?
A halogenoalkane is an organic compound containing one or more halogen atoms (F, Cl, Br or I) bonded to a carbon chain, classified as primary, secondary or tertiary depending on the number of alkyl groups attached to the carbon bearing the halogen.
A polyester is formed from .......... and .......... monomers; the monomers are linked by .......... bonds.
A polyester is formed from dicarboxylic acid and diol monomers; the monomers are linked by ester bonds.
True or False?
Nylon 6,6 is made from monomers that each contain six carbon atoms.
True.
Nylon 6,6 is made from 1,6-diaminohexane and 1,6-hexanedioic acid, each containing six carbon atoms, which gives rise to the "6,6" in its name.
Why is a diacyl dichloride used in place of the dicarboxylic acid when making Nylon 6,6 in the laboratory?
The reaction between a diamine and a dicarboxylic acid is slow.
The diacyl dichloride is a more reactive monomer, so it reacts with the diamine much faster, though it is more expensive.
Kevlar® is an aromatic polyamide made from .......... and .......... monomers. Its high strength arises from the large number of .......... bonds between adjacent polymer chains.
Kevlar® is an aromatic polyamide made from 1,4-benzenediamine and 1,4-benzenedicarboxylic acid monomers. Its high strength arises from the large number of hydrogen bonds between adjacent polymer chains.
True or False?
PET (Terylene) can only be formed from two separate monomers — a diol and a dicarboxylic acid.
False.
PET can also be formed from a single hydroxycarboxylic acid monomer, which contains both the –OH and –COOH groups needed for polymerisation.
What are aramids and give two examples?
Aramids are aromatic polyamides — condensation polymers with benzene rings linked by amide bonds.
Examples: Kevlar® (used in bulletproof vests) and Nomex® (used in fireproof suits).
Why does Kevlar® have a higher melting point than Nomex®, even though both are aramids?
Kevlar® chains are straighter and lie closer together, so they form more effective hydrogen bonds between adjacent chains.
The greater number of stronger hydrogen bonds gives Kevlar® a higher melting point.
Why are condensation polymers described as biodegradable while addition polymers are not?
Condensation polymers contain ester or amide links that can be hydrolysed by acid catalysts or enzymes, breaking the polymer into smaller fragments.
Addition polymers (polyalkenes) contain only C–C bonds between monomers, which are inert and cannot be hydrolysed.
True or False?
Polyalkenes are non-biodegradable because the C–C bonds linking their monomers cannot be hydrolysed.
True.
Polyalkenes are formed by addition polymerisation and contain only inert C–C bonds between monomers, so they cannot be broken down by hydrolysis reactions.
The rate of hydrolysis of a biodegradable polymer in the environment is affected by factors including .........., .........., bacterial content and access to .......... light.
The rate of hydrolysis of a biodegradable polymer in the environment is affected by factors including moisture content, oxygen levels, bacterial content and access to UV light.
State one advantage and one disadvantage of disposing of polymers by incineration.
Advantage: reduces landfill volume; energy released can be used to generate electricity.
Disadvantage: burning polymers can release toxic gases (e.g. HCl from PVC) and contributes to air pollution and CO2 emissions.
There are three main methods of disposing of polymers: .........., .......... and .......... .
There are three main methods of disposing of polymers: landfill, incineration and recycling.
True or False?
Recycling polymers is always the most environmentally friendly disposal method regardless of the polymer type.
False.
Recycling requires energy for collection, sorting and processing, and not all polymers can be recycled easily. The best method depends on the polymer type and local infrastructure.
State the reagents and conditions used to hydrolyse a condensation polymer chemically.
Concentrated hydrochloric acid, heated for many hours (the reaction is slow).
Alternatively, enzymes can catalyse hydrolysis at room temperature.
Biodegradable
A material is biodegradable if it can be broken down by microorganisms (or by hydrolysis catalysed by acids or enzymes) into simpler substances in the environment. Condensation polymers (polyesters and polyamides) are biodegradable; addition polymers (polyalkenes) are not.
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