Physical structure of polymers

There are three basic physical polymer structures: linear, branched, and cross-linked.

Linear polymers resemble spaghetti due to their long chains of monomers. The chains interact through weak intermolecular forces. Upon subsequent heating and cooling, these weak bonds easily break and reform, meaning we can remold the material, a property called thermoplasticity.

Branched polymers have shorter or longer side-chains hanging from the long linear backbone. These side-chains push neighboring chains away, resulting in a lower density compared to linear polymers. Branched polymers are mostly thermoplastic, but some might have such complex branching that they tangle up, resisting melting, also known as thermosetting.

Cross-linked polymers are polymers where strong bonds exist between neighboring chains/branches. Cross-links are strong and restrict relative movement between the chains, meaning that cross-linked polymers are thermosetting.

Figure 1. Linear, branched, and cross-linked polymers