What type of thermoplastic is characterized by having a glass transition temperature rather than a true melting point?

Amorphous thermoplastics are characterized by having a glass transition temperature (Tg) instead of a true melting point. The glass transition temperature is the temperature range in which the polymer transitions from a hard and relatively brittle state into a more flexible or rubbery state. This behavior occurs because amorphous thermoplastics lack a well-defined crystalline structure, which means they do not exhibit a distinct melting point like crystalline thermoplastics do. Instead, they gradually soften over a range of temperatures as the molecular chains gain mobility.

Understanding this distinction is crucial, as it impacts how these materials are processed and used in various applications. For example, when heated beyond the Tg, amorphous thermoplastics can be molded and reshaped. This property is beneficial in manufacturing processes such as injection molding or 3D printing, where precise control over the material's flow and shape is necessary.