Among tacticities, which has the highest crystallinity generally?

• A. Isotactic
• B. Syndiotactic
• C. Atactic
• D. Random

Answer: (D)

Crystallinity in polymers comes from how regularly the chain can stack in a crystal lattice. When the stereochemistry along the chain is uniform, the chains line up more predictably, allowing close, ordered packing. If all the substituents are on the same side (isotactic), the chains are highly regular in three dimensions, so they form crystalline regions and exhibit the highest crystallinity. If the substituents alternate sides (syndiotactic), packing is still regular but not as favorable as isotactic, so crystallinity is high but typically lower than isotactic. If the arrangement is random or irregular (atactic or random), long-range order is disrupted and the material becomes largely amorphous with very low crystallinity. Therefore, the highest crystallinity generally comes from isotactic configurations.