Which form of polypropylene has higher crystallinity?

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

Answer: (B)

Crystallinity in polypropylene is determined by tacticity, which is how regularly the methyl side groups are arranged along the polymer backbone. When all the methyl groups point the same way, as in the isotactic form, the chains can pack very orderly into a repeating lattice and form well-developed crystalline regions (lamellae). This regular packing gives the highest degree of crystallinity and a higher melting point.

In the atactic form, the methyl groups are positioned randomly, which disrupts orderly packing and leads to mostly amorphous material with low crystallinity. The syndiotactic form has an alternating arrangement of methyl groups, which is regular and allows some crystallization, but the packing is not as optimal as in the isotactic form, so its crystallinity is lower than isotactic.

So the isotactic form has the highest crystallinity.