Which statement best describes linear polymer structure?

• A. A chain-like but very rigid backbone
• B. A network with extensive cross-links
• C. A dendritic branched architecture
• D. A chain-like structure that is highly flexible

Answer: (D)

Linear polymers are built from long, essentially unbranched chains with little to no covalent cross-links. This chain-like architecture allows the backbone to rotate and the chains to slide past one another, giving high mobility and, for many common polymers, substantial flexibility at typical temperatures. Therefore, describing a chain-like structure that is highly flexible captures the defining feature of linear polymers: long, unbranched chains that can move relative to each other.

The other descriptions point to different architectures. A chain with a very rigid backbone implies stiffness rather than the flexible behavior typical of many linear polymers. A network with extensive cross-links describes a crosslinked thermoset, not a linear polymer. A dendritic branched architecture refers to highly branched molecules, not linear chains.