Question

Which of the following represents a semi-crystalline polymer?

• A. Polyethylene
• B. Polycarbonate
• C. Epoxy
• D. Bakelite

Hint:

Linear polymers with simple, symmetrical repeating units (like polyethylene and polytetrafluoroethylene) crystallize easily, whereas polymers with bulky side groups or cross-linked networks remain amorphous.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify which of the given polymers exhibits a semi-crystalline structure.
In polymer science, structural order varies significantly.
Polymers can be amorphous (completely disordered), crystalline (highly ordered), or semi-crystalline (containing both crystalline and amorphous regions).

Step 2: Detailed Explanation:

• Structure of Semi-Crystalline Polymers: Semi-crystalline polymers possess a structural model consisting of highly ordered crystalline lamellae interspersed with disordered amorphous regions.
The linear and highly symmetrical chain structure of polyethylene (PE) allows its chains to pack efficiently into ordered crystalline arrays.
Consequently, polyethylene exhibits a high degree of crystallinity, typically ranging from \( 35\% \) to \( 80\% \), depending on the branch density (e.g., HDPE vs. LDPE).

• Amorphous Thermoplastics: Polycarbonate (Option B) contains bulky bisphenol-A aromatic rings along its backbone.
These large side groups prevent the chains from aligning and packing into an ordered crystal lattice, making polycarbonate a completely amorphous thermoplastic with high optical clarity.

• Thermosetting Polymers: Epoxy (Option C) and Bakelite (Option D) are thermosetting polymers.
During curing, they form a highly cross-linked, three-dimensional network structure.
These permanent chemical cross-links restrict molecular movement and prevent crystallization, resulting in a strictly amorphous solid network.


Step 3: Final Answer:
Therefore, Polyethylene represents a semi-crystalline polymer, matching Option (A).