Polymethyl methacrylate (PMMA), also called Perspex or acrylic glass, is produced by bulk polymerisation of methyl methacrylate. PMMA is not a/an ______ polymer. Select the most accurate completion.

Introduction / Context:
PMMA (acrylic glass) is widely used for glazing, lenses, and transparent housings because of its clarity and weatherability. Understanding whether PMMA behaves as a thermoplastic or thermoset informs processing options (injection molding, extrusion, thermoforming) and recyclability.

Given Data / Assumptions:

• Methyl methacrylate undergoes chain-growth (addition) polymerisation to PMMA.
• PMMA exhibits glass-like transparency and is moldable.
• Thermoplastics can be reheated and reshaped below their degradation temperature.

Concept / Approach:
PMMA is a linear (though possibly lightly branched) addition polymer. It softens upon heating and can be remolded, which is characteristic of thermoplastics, not thermosets. Thermosets form infusible, three-dimensional networks that do not melt. Therefore, the statement correctly completed is that PMMA is not a thermosetting polymer.

Step-by-Step Solution:

Verification / Alternative check:
Processing guides show PMMA being injection molded and thermoformed, which are thermoplastic processes.

Why Other Options Are Wrong:

• Thermoplastic/linear/glass-like transparent/amorphous optical-grade: all describe PMMA accurately.

Common Pitfalls:
Confusing “glassy” appearance with “thermoset”; glassy refers to the amorphous state above brittleness, not network chemistry.

Final Answer:
Thermosetting