Which statement about crystallization and tensile strength in isotactic and syndiotactic polymers is correct?

• A. Syndiotactic polymers never crystallize
• B. Iso- and Syndiotactic polymers both crystallize equally; Syndiotactic PS has higher MW and thus higher TS
• C. Tacticity does not influence crystallization or TS
• D. Isotactic PS has higher TS regardless

Answer: (B)

Regular arrangement of stereochemistry along the chain influences how well chains can pack into crystals, which in turn affects crystallinity and mechanical strength. Isotactic and syndiotactic arrangements provide enough regularity for crystallization to occur, unlike atactic polymers which are typically amorphous.

Tensile strength grows with crystallinity and with molecular weight. Higher molecular weight means longer chains and more entanglements, which improve load transfer and resistance to stretching. So, if a syndiotactic sample has a higher molecular weight, it can exhibit higher tensile strength.

The idea captured here is that both isotactic and syndiotactic PS can crystallize, and tensile strength is enhanced by higher molecular weight. The other statements misrepresent crystallization in syndiotactic polymers, deny the influence of tacticity, or assert an absolute rule about isotactic strength that isn’t generally true.