4.13 Compare thermoplastic and thermosetting polymers (a) on the basis of mechanical characteristics upon heating and (b) according to possible molecular structures.

a. The thermoset polymer can only be heated once, that is when heated it cannot be reheated for remolding purposes. When this polymer is heated its strength increases. On the other hand thermoplastic polymers can be heated multiple times, and remolded without affecting its chemical make up.

b. The molecular structure of thermoset polymers are strong covalent cross links, while the structure of thermoplastic polymers is linear and flexible allowing for the reheating and molding.