Which statement correctly describes heating behavior of thermoplastics versus thermosets?

• A. Thermoplastics degrade upon heating; Thermosets degrade and do not melt
• B. Both Thermoplastics and Thermosets melt upon heating
• C. Thermosets melt; Thermoplastics vaporize
• D. Therosets degrade upon heating; Thermoplastics melt upon heating

Answer: (D)

The heating behavior is governed by the polymer’s network structure. Thermoplastics are composed of long chains with no permanent crosslinks, so when heated above their melting temperature the chains gain mobility and the material melts and can be reshaped. Thermosets, once cured, form a rigid three‑dimensional crosslinked network that locks the structure in place, so they do not flow or melt when heated. Instead, they tend to degrade or decompose at high temperatures, sometimes charing rather than melting. That contrast—thermoplastics melting and thermosets degrading—is why the statement is correct.