From models to materials: notes and practice questions
- This topic covers the formation and breakdown of condensation polymers and biological macromolecules.
- Condensation polymers form when functional groups in monomers react, releasing a small molecule.
- Students must be able to represent the repeating unit of polyamides and polyesters from given monomer structures.
- All biological macromolecules, such as proteins and polysaccharides, are formed by condensation reactions and break down by hydrolysis.
How it is examined
Bonding triangle questions give the electronegativity data and ask for a position or a predicted property, 1 to 2 marks. Polymer questions run both ways: draw the repeating unit from monomers, or deduce the monomer from a drawn polymer. May 2025 HL Paper 2 TZ1 asked candidates to deduce the monomer that forms a given polymer [1] and then describe a chemical property that makes it useful [1]. The repeating-unit convention (brackets, continuation bonds through the brackets, subscript n) is marked, so a drawing without the trailing bonds can be refused.
The bonding triangle and electronegativity values. Everything else is recall or is supplied in the question stem, including monomer structures.
- 2.4.1 Bonding is best described as a continuum between the ionic, covalent and metallic models, and can be represented by a bonding triangle. Students use bonding models to explain the properties of a material.
- 2.4.2 The position of a compound in the bonding triangle is determined by the relative contributions of the three bonding types to the overall bond. Students determine the position of a compound in the bonding triangle from electronegativity data, and predict the properties of a compound based on its position.
- 2.4.3 Alloys are mixtures of a metal and other metals or non-metals. They have enhanced properties. Students explain the properties of alloys in terms of non-directional bonding.
- 2.4.4 Polymers are large molecules, or macromolecules, made from repeating subunits called monomers. Students describe the common properties of plastics in terms of their structure.
Calculations of percentage ionic character are not required. The bonding triangle is read off, not computed into a percentage.
Guiding questions
- What role do bonding and structure have in the design of materials?
Linking questions
- Structure 3.1 How do the trends in properties of period 3 oxides reflect the trend in their bonding?
- Nature of science, Structures 2.1, 2.2 What are the limitations of discrete bonding categories?
- Structure 2.1, 2.2, 2.3 Why do composites like reinforced concretes, which are made from ionic and covalently bonded components and steel bars, have unique properties?
- Structure 1.1 Why are alloys more correctly described as mixtures rather than as compounds?
- Structure 3.2 What are the structural features of some plastics that make them biodegradable? What functional groups in molecules can enable them to act as monomers for addition reactions? (HL) for condensation reactions?
- Reactivity 2.1 Why is the atom economy 100% for an addition polymerization reaction?
- Structure 3.2 (HL) What is the nature of the reaction that occurs when two amino acids form a dipeptide?
Practice questions
4 questions · 3 medium · 1 hardQuestion 1
MediumPaper 2 · calculator3 marks(a) Nylon-6,6 is a synthetic polyamide produced by the condensation polymerisation of hexane-1,6-diamine, , and hexanedioic acid, .
Deduce the molecular formula of the repeating unit of nylon-6,6.
(b) State the name of the functional group linking the monomer units together in nylon-6,6.
Consider the total number of carbon, hydrogen, nitrogen, and oxygen atoms in one molecule of each monomer. Remember that condensation polymerisation between a diamine and a dicarboxylic acid eliminates two water molecules () per complete repeating unit.
Identify the functional group that forms when a primary amino group reacts with a carboxylic acid group with the elimination of water.
Question 2
HardPaper 2 · calculator3 marksA synthetic polyester used in biomedical devices has the repeating unit:
Deduce the structural formulas of the two monomers used to synthesize this polyester.
(b) A polyamide used in specialized textiles has the repeating unit:
Deduce the structural formula of the single monomer from which this polyamide is formed.
Identify the ester linkage in the repeating unit and determine which components derive from a dialcohol (diol) and a dicarboxylic acid by adding back the elements of water (H and OH).
Notice that the repeating unit contains both an amine residue and a carbonyl residue from an amide bond within the same repeating unit. Add the components of water (H to the amine, OH to the carbonyl) to reconstitute the bifunctional monomer.
Question 3
MediumPaper 1A · calculator1 markPropane-1,3-diamine, , reacts with butanedioic acid, , to form a polyamide.
Which structure represents the repeating unit of the polymer?
A.
B.
C.
D.
Consider what small molecule is eliminated when an amine group reacts with a carboxylic acid group, and identify which atoms are lost from each functional group. Then check the number of units in the chain of each monomer.
Question 4
MediumPaper 2 · calculator2 marksPoly(butylene succinate), PBS, is a biodegradable polyester synthesized from butane-1,4-diol, , and butanedioic acid, .
Explain how this condensation polymer forms from its monomers, with reference to the functional groups involved and any other molecule produced.
Consider the reactive functional groups present on each monomer, the new functional linkage formed between them, and the small molecule eliminated in each step of the chain growth.
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Where marks are lost
- Reaching for "human error" or "only one trial." A source of error has to be a specific step in the method, not a general apology for the result.
- Joining the dots instead of drawing a curve.
- Naming a chemical instead of the property that distinguishes it, or vice versa. Answering with the nearest fact that comes to mind rather than the fact the command term and stem jointly ask for is a recurring way to answer a question that was not, quite, the one asked.
