Which of the following polymers in thermosetting?

Step 1: Analyze the question We need to identify which polymer is thermosetting.

Step 2: The concept

• Thermosetting plastics are polymers that harden permanently when heated and moulded. Their chains form strong cross-links (a rigid 3D network), so they cannot be softened or remelted. Reheating them just chars or decomposes them.
• Thermoplastics soften when heated and harden when cooled. They have linear or slightly branched chains with weak intermolecular forces, so they can be remelted and reshaped repeatedly.

Step 3: Check each option

• A. Bakelite: made from phenol and methanal (formaldehyde). It has a heavily cross-linked network, so it is thermosetting. It is used for electrical fittings, switches, and pot handles.
• B. Nylon: a polyamide with linear chains. It is a thermoplastic, used for fibres, ropes, and fabrics.
• C. Polypropene: an addition polymer with linear chains. It is a thermoplastic, used for containers and ropes.
• D. Polystyrene: an addition polymer from styrene. It is a thermoplastic, used for packaging and insulation.

Step 4: Answer Only Bakelite has a cross-linked structure that sets permanently, so the correct option is A. Bakelite.

Exam tip: Remember the thermosetting examples with the phrase "Bake Me Up": Bakelite, Melamine (melamine-formaldehyde), Urea-formaldehyde (plus Phenol-formaldehyde). Most other common plastics in WASSCE questions (polythene, PVC, polystyrene, nylon, perspex) are thermoplastics.