Polymers Extension questions
1 Look closely at the structures of glycine and glutamic acid shown below.
a) Using glycine as an example, explain what you understand by the isoelectric point of
an amino acid.
b) The isoelectric point of glycine is at pH = 6.0. Why is the isoelectric point of glycine not
at pH = 7?
c) How do you think the isoelectric point of glutamic acid will compare with that of
glycine? Explain your answer.
2 a) Poly(ethenol) is made from ethenyl ethanoate,
Ethenyl ethanoate is first polymerised to produce poly(ethenyl ethanoate). This is then
converted to poly(ethenol) by replacing about 90% of the CH3COO groups in
poly(ethenyl ethanoate) with OH groups.
i) Draw the structure of ethenol and the repeat unit in pure poly(ethenol).
ii) Draw the repeat unit in poly(ethenyl ethanoate).
iii) Calculate the relative molecular mass of a sample of poly(ethenol) containing
2000 monomer units in which 10% of the monomer units contain CH3COO groups
which have not been replaced by OH groups.
iv) Why is poly(ethenol) soluble in water?
b) The solubility in water of poly(ethenol) depends on the percentage of CH3COO
groups replaced. Maximum solubility in water occurs when about 88% of the
CH3COO groups are replaced by OH groups. If fewer groups are replaced, the
poly(ethenol) becomes less soluble.
When more CH3COO groups are replaced, the solubility decreases and when all
the groups are replaced, the poly(ethenol) is insoluble in water.
i) Why does poly(ethenol) become less soluble if fewer CH3COO groups are
replaced by OH groups?
ii) Why do you think the solubility decreases when more than 88% of the CH3COO
groups are replaced by OH groups?
iii) When all the CH3COO groups are replaced by OH groups, the poly(ethenol)
crystallises and becomes insoluble in water. Suggest what may have happened
to make the poly(ethenol) insoluble?
3 This question is concerned with the molecular interactions between the polymer chains
in various plastics.
a) Tables of data show that the melting temperatures of low density polythene and high
density polythene differ by 23 C.
i) What type of molecular interactions occur between polythene molecules?
ii) Why are the densities of the two polythenes different?
iii) Suggest which type of polythene has the higher melting temperature and explain
b) The same tables of data show no melting temperature for Bakelite. Why is this?
c) The polymer Kevlar is a polyamide with a much higher melting temperature than
i) Explain the term polyamide.
ii) Kevlar is manufactured from the monomers benzene 1,4-dicarboxylic acid and
benzene 1,4-diamine. Draw the structure of one repeat unit in a molecule of
iii) What is the strongest type of intermolecular force in Kevlar?
iv) Which atoms and groups are involved in the strongest type of intermolecular
force in Kevlar?
d) Kevlar is a very strong polymer as it contains crystalline regions.
i) How does the arrangement of Kevlar molecules differ in crystalline regions and
ii) Why do the crystalline regions help to make Kevlar strong?