Question

Which of the following you expect to be crystalline polymer

• A. Polybutadiene
• B. Nylon 66
• C. Cis polyisoprene
• D. Polychloroprene

Hint:

Strong intermolecular forces like hydrogen bonding promote polymer crystallinity.

Answer 1

The Correct Option is B

Step 1: Understanding crystallinity in polymers.
Crystalline polymers have regularly arranged chains that pack closely, leading to ordered regions. Strong intermolecular forces favor crystallinity.
Step 2: Structure of Nylon 66.
Nylon 66 contains repeating amide groups (–CONH–) that form strong hydrogen bonds between polymer chains, allowing them to align and crystallize efficiently.
Step 3: Analysis of options.
(A) Polybutadiene: Mostly amorphous elastomer.
(B) Nylon 66: Correct — Highly crystalline due to hydrogen bonding.
(C) Cis polyisoprene: Natural rubber, largely amorphous.
(D) Polychloroprene: Elastomer with low crystallinity.
Step 4: Conclusion.
Nylon 66 is expected to be a crystalline polymer, hence option (B) is correct.

Answer 2

Crystallinity in a polymer depends on how regularly and symmetrically the chains can line up next to each other, so look at the backbone regularity of each option rather than just the presence of strong bonding.

1. Polybutadiene: Contains cis and trans double bonds distributed somewhat irregularly along the chain (depending on the polymerization method), and the flexible, kinked diene backbone does not line up into a tight, repeating lattice easily, keeping it largely amorphous.
2. Nylon 66: Is built from a perfectly alternating, regular sequence of two symmetric monomers (hexamethylenediamine and adipic acid), giving a highly regular zig-zag backbone. This regularity, combined with the repeating amide groups that hydrogen-bond between neighboring chains, allows the chains to align into a dense, ordered crystal lattice very efficiently.
3. Cis polyisoprene: The cis double bond configuration puts a permanent kink at every repeat unit, which prevents the chains from packing into a regular lattice under normal conditions (it only crystallizes on stretching or at very low temperature), so it is largely amorphous at room temperature.
4. Polychloroprene: While it can crystallize somewhat, especially on stretching, the mixture of possible isomer sequences along its backbone (due to different possible addition modes of chloroprene) disrupts perfect regularity, giving it lower and slower crystallinity than a fully regular polymer like nylon.

Because Nylon 66's backbone is both highly regular and reinforced by interchain hydrogen bonds, it is the one that packs into the most ordered, crystalline structure.

Therefore, the correct answer is Nylon 66.