Covers Lessons 21–23: Addition and condensation polymers — mechanism, drawing structures, common polymers and uses, biopolymers, thermoplastics vs thermosets, and environmental impact.
1. Which statement correctly identifies the monomer of PTFE and explains its extreme chemical resistance?
2. The repeat unit of a condensation polymer is [–O–(CH₂)₂–O–CO–C₆H₄–CO–]ₙ. What type of polymer is this and what are its monomers?
3. Which statement correctly distinguishes cellulose from starch?
4. A thermoplastic softens and flows on heating; a thermoset does not. What is the structural reason?
5. Nylon 6,6 is a condensation polymer. Which feature MOST directly demonstrates this?
MC Answers: 1-A | 2-B | 3-B | 4-B | 5-C
1-A: PTFE monomer = CF₂=CF₂. C–F bonds (~485 kJ/mol) are among the strongest to carbon. F atoms are small and electronegative, packing tightly around the backbone → no common reagent can attack. Option C wrongly cites molecular mass as the reason.
2-B: The –COO– linkage in the repeat unit is an ester bond → polyester. Breaking at each ester bond by inserting H₂O: –O–(CH₂)₂–OH = ethylene glycol; HOOC–C₆H₄–COOH = terephthalic acid → this is PET. Option C (polyamide) would have –CO–NH– not –COO–.
3-B: Same monomer (glucose) but different glycosidic bond geometry. β-1,4 (cellulose): straight chains → H-bonded microfibrils → rigid, indigestible. α-1,4 (starch): helical → digestible by human amylase. Both are condensation polymers (option D is wrong).
4-B: Thermoplastic chains are held by IMF (dispersion, H-bonds, dipole-dipole) — these weaken reversibly → softens on heating → remoulding possible. Thermoset covalent cross-links are not broken by moderate heating → chars/decomposes instead of flowing.
5-C: The defining feature of condensation polymerisation is release of a small molecule (H₂O here) at every bond formed. Using two monomers (option A) is consistent with but not unique to condensation. Physical properties (B, D) are not diagnostic.
SA1 (5 marks):
(a) Monomers: ethylene glycol (HOCH₂CH₂OH) + terephthalic acid (HOOC–C₆H₄–COOH). Repeat unit: [–O–CH₂CH₂–O–CO–C₆H₄–CO–]ₙ (open bonds at brackets, n subscript). Label: ester linkage –COO– (appears twice per unit). By-product: H₂O (2 mol per repeat unit). [2 + 1 marks]
(b) Chemical: PET's ester bonds are hydrolysable (acid/base/enzymatic) → monomers can be recovered and repolymerised (closed-loop recycling) — more efficient than incineration [1]. Environmental: PET in landfill degrades over centuries; in oceans it fragments to microplastics that accumulate in food chains; recycling reduces both pollution and fossil fuel demand for virgin PET [1].
SA2 (4 marks):
Silk: contains amide (peptide) bonds; ubiquitous proteases in soil bacteria hydrolyse peptide bonds → silk degrades in weeks to months [1]. Nylon 6,6: also has amide bonds (theoretically hydrolysable) BUT nylon's uniform crystalline packing limits enzyme access, and no common soil enzyme evolved to degrade synthetic nylon → degrades over decades to centuries [1]. Polyethylene: C–C backbone only — cannot be hydrolysed; no known biological enzyme cleaves it; only UV photolysis produces microplastics → effectively non-biodegradable on any human timescale [1]. Order: silk >> Nylon 6,6 >> polyethylene. Chemical basis: hydrolysable amide bonds → biodegradable; C–C only backbone → non-biodegradable [1].
Tick when you have finished all questions.