Animated Solution for Chemistry - Polymers: Choose the correct option(s) from the following

A Deep Dive into Natural Rubber, Nylon-6, Cellulose, and Teflon

When tackling questions on polymers in competitive exams like JEE, success often hinges on your ability to recall specific structural details, monomers, and the types of linkages that hold the polymer chains together. Let's break down the four statements provided in this question to understand exactly why each is either correct or incorrect.

The first statement claims that natural rubber is polyisoprene containing trans alkene units. While it is true that natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene), the geometric configuration of the double bonds in the polymer chain is strictly cis.

This cis-1,4-polyisoprene structure prevents the polymer chains from packing closely together, which is precisely what gives natural rubber its characteristic elasticity. If the double bonds were in the trans configuration, the chains would pack tightly, forming a hard, non-elastic material known as gutta-percha. Therefore, statement (A) is incorrect.

The second statement asserts that Nylon-6 has amide linkages. Nylon-6 is synthesized by heating caprolactam with water at high temperatures. Caprolactam is a cyclic amide containing six carbon atoms.

During polymerization, the ring opens up, and the molecules link together to form a long chain. Because the monomer itself contains an amide group, the resulting polymer chain is held together by repeating amide linkages ($-\text{CO}-\text{NH}-$). This makes Nylon-6 a polyamide, confirming that statement (B) is absolutely correct.

The third statement suggests that cellulose consists of $\alpha$-D-glucose units. Cellulose is indeed a straight-chain polysaccharide and a major structural component of plant cell walls. However, it is composed exclusively of $\beta$-D-glucose units joined by $\beta$-1,4-glycosidic linkages.

It is starch (specifically amylose and amylopectin) that is made up of $\alpha$-D-glucose units. The difference between the $\alpha$ and $\beta$ anomers might seem small, but it drastically changes the physical properties of the polymer. The $\beta$ linkages allow cellulose to form strong, rigid fibers, whereas $\alpha$ linkages cause starch to coil. Thus, statement (C) is incorrect.

The final statement describes the preparation of Teflon. Teflon, chemically known as polytetrafluoroethylene (PTFE), is manufactured by the addition polymerization of tetrafluoroethene gas (${\text{CF}}_2={\text{CF}}_2$).

This reaction is carried out under high pressure and requires a free radical initiator to kickstart the polymerization process. A commonly used initiator for this reaction is a persulphate catalyst, which decomposes to provide the necessary free radicals. This perfectly aligns with the description given, making statement (D) correct.

By carefully evaluating the structural chemistry and synthesis conditions of these common polymers, we can confidently conclude that the correct options are (B) and (D).