Polymers are often grouped as thermosetting, thermoplastic, elastomer, and fibre. On what fundamental basis is this textbook classification primarily made?

Introduction / Context:
Introductory polymer science courses classify polymers into thermoplastics, thermosets, elastomers, and fibres. This grouping correlates mechanical/thermal behaviour with how strongly chains attract each other and whether they are crosslinked. Understanding the underlying basis helps predict processing and performance.

Given Data / Assumptions:

• Intermolecular forces include hydrogen bonding, dipole–dipole, and dispersion interactions.
• Crosslink density also effectively increases “interchain constraint,” behaving like very strong interactions.
• The question asks for the primary basis used in classic textbooks.

Concept / Approach:
Stronger intermolecular forces (or network crosslinking) yield rigid, high-modulus materials (fibres, thermosets). Weaker forces produce flexible, low-modulus materials (elastomers). Thermoplastics sit between, softening with heat due to reversible weakening of secondary forces. Thus, the classic categorisation is fundamentally tied to the magnitude of interchain forces and constraints.

Step-by-Step Solution:
Relate category to chain interactions: fibres/thermosets (strong), thermoplastics (moderate), elastomers (weak but lightly crosslinked).Eliminate alternatives that are secondary (mechanism) or incomplete (size only).Select “magnitude of intermolecular forces.”

Verification / Alternative check:
Standard texts map tensile modulus, Tg, and thermal behaviour to interchain forces/crosslinking, aligning with the four groups.

Why Other Options Are Wrong:
Molecular size alone: insufficient—similar Mw polymers can behave differently.Heat resistance: a result, not the class basis.Polymerisation mechanism: step- vs chain-growth does not directly define these four end-use categories.Crystallinity alone: important but not the primary basis.

Common Pitfalls:
Assuming synthesis route dictates class; behaviour is dominated by interchain forces and crosslinking.

Final Answer:
Magnitude of intermolecular forces