How do amorphous polymers differ from semicrystalline polymers?

Amorphous and semicrystalline polymers differ primarily in their molecular arrangement and resulting physical properties.12

Molecular Structure

• Amorphous Polymers: These consist of randomly oriented, intertwined molecular chains, often compared to cooked spaghetti. They lack long-range order.123
• Semicrystalline Polymers: These contain both amorphous regions and ordered, tightly packed regions known as crystallites. Linear polymers with regular structures are more likely to exhibit this morphology.12

Physical Properties

• Appearance: Amorphous polymers typically appear transparent and glasslike, whereas the presence of crystallites in semicrystalline polymers scatters light, making them more opaque.1
• Mechanical Strength: Semicrystalline polymers generally form tougher plastics due to the strong intermolecular forces within their crystallites.1
• Thermal Behavior: While both types exhibit a glass transition temperature ($T_g$), semicrystalline polymers also possess a distinct melting temperature ($T_m$) at which their crystalline regions become unstable. Amorphous polymers transition directly from a rubbery state to a liquid state upon heating.12