Thermosets versus thermoplastics: which statement correctly characterises thermosetting polymers?

Introduction / Context:
Thermosetting polymers and thermoplastics differ in processing and final network architecture, which determines recyclability, heat resistance, and solvent response.

Given Data / Assumptions:

• Thermosets cure into infusible networks.
• Thermoplastics soften on heating and can be remoulded.
• Polymerisation mechanisms may be step-growth (condensation) or chain-growth (addition) depending on the system.

Concept / Approach:
The defining feature of a thermoset is its three-dimensional crosslinked network formed during cure. This network prevents flow upon reheating and affords high heat and chemical resistance. In contrast, thermoplastics are typically linear or lightly branched and can be reprocessed.

Step-by-Step Solution:
Identify the structural hallmark of thermosets: crosslinking into a 3D network.Eliminate statements describing linear, melt-reprocessable behaviour.Select the option that states the crosslinked 3D structure.

Verification / Alternative check:
Examples: epoxies, phenolics, and melamines are thermosets; polyethylene and polypropylene are thermoplastics.

Why Other Options Are Wrong:
(a) Some thermosets are not formed by addition; many cure via step-growth.(c) Describes thermoplastics, not thermosets.(d) Incorrect because (b) is correct.

Common Pitfalls:
Confusing polymerisation mechanism with final network structure; assuming all crosslinked materials are made by addition.

Final Answer:
They possess a three-dimensional crosslinked structure after cure.