Which statement describes crystallization tendencies of isotactic and syndiotactic polymers?

• A. Iso- and Syndiotactic polymers both crystallize equally
• B. Only isotactic polymers crystallize
• C. Syndiotactic polymers cannot crystallize
• D. Crystallization is entirely independent of tacticity

Answer: (A)

The main idea is that chain regularity, created by tacticity, governs a polymer’s ability to crystallize. Isotactic and syndiotactic polymers both have highly regular sequences of side groups along the chain, just arranged differently: all the same orientation in isotactic and an alternating orientation in syndiotactic. This regularity lets the chains pack into ordered, crystalline lattices. The two forms form their own distinct crystal structures and may crystallize at different rates or to different extents, but they both can crystallize. In contrast, atactic polymers, with random side-group orientations, usually stay amorphous because the irregularity disrupts regular packing. So stating that both isotactic and syndiotactic polymers crystallize captures the idea that tacticity promotes crystallization, while the two forms may crystallize with different crystallography or kinetics.