Problem 96 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is/are correct about spandex? (I) It is a poly urethane (II) It is a flexible polymer (III) It is a polymer of toluene 2,6 di isocyanate and glycol (IV) It is a polymer of ammonum carbamate (a) I, II, III (b) I, II, IV (c) II, II, IV (d) I, II, III, IV

Step-by-Step Solution

Answer

The correct answer is (a) I, II, III.

Step 1: Understanding Spandex Composition

Spandex is a synthetic polymer known for its exceptional elasticity. The chemical structure of spandex is primarily based on polyurethane, which derives from a polyaddition reaction between polyether or polyester polyols and diisocyanates. Hence, it matches the description in statement (I).

Step 2: Evaluating Flexibility of Spandex

Spandex is widely recognized for its flexibility and elasticity. This is due to its molecular structure allowing for significant elongation. This aligns with statement (II), indicating its flexibility as a polymer.

Step 3: Analyzing Polymer Components

Commonly, spandex is synthesized using toluene diisocyanate and glycol. When considering the statement (III), it correctly lists toluene 2,6 diisocyanate and glycol as part of its polymer components. So, statement (III) is correct.

Step 4: Verifying Statement about Ammonium Carbamate

Ammonium carbamate is not related to the production or composition of spandex. This does not align with spandex's known synthesis materials, making statement (IV) incorrect.

Step 5: Conclusion

After evaluating each statement, statements (I), (II), and (III) are correct, while statement (IV) is incorrect. Therefore, the correct answer is option (a).

Key Concepts

Polyurethane

Polyurethane is an incredibly versatile polymer that plays a crucial role in the creation of materials like spandex. It forms through a reaction known as polyaddition. This reaction involves combining polyols, which can be either polyester or polyether-based, with diisocyanates. During this chemical process, the ingredients amalgamate to form a long chain, creating a structure characterized by many repeating units, or "mers." These chains are responsible for the distinctive elasticity and resilience of polyurethane.
Polyurethane is used in numerous applications, ranging from foams and elastomers to coatings and adhesives. Its adaptability and durability come from its ability to be molded into various forms, offering both flexibility and toughness. This makes it an ideal candidate for producing flexible polymers like spandex. Spandex, in particular, owes its signature stretchiness and recovery properties to the polyurethane backbone, enabling garments to fit closely to the body while maintaining comfort.

Flexible Polymers

Flexible polymers, as their name implies, are plastically adaptable, allowing them to be stretched and reshaped without breaking. This flexibility comes from the molecular structure of these polymers, which includes long chain-like molecules that can slide past each other under stress. Spandex is an exemplary model of a flexible polymer.
Its elasticity is attributable to the presence of soft, stretchable segments within its polymer chains. These segments allow the fibers to be stretched considerably and return to their original form, making them highly valuable in industries where products are expected to respond to dynamic conditions.
Applications of flexible polymers extend beyond textiles. They are used in packaging, automotive parts, medical devices, and more. Their ability to handle stress and deformation while maintaining integrity is key to their functionality in a wide range of products. This pliability is why materials like spandex are preferred in making comfortable, form-fitting clothing.

Diisocyanates in Polymers

Diisocyanates are essential chemical compounds in the production of polyurethanes, including spandex. These compounds typically have two isocyanate groups, which are crucial for forming cross-links with polyols during the polymerization process. The most common diisocyanates found in spandex are toluene-2,6-diisocyanate and methylene diphenyl diisocyanate.
When these diisocyanates react with glycols or other polyols, they create long, net-like structures that lend strength and durability to the polymer. They help create a balance between flexibility and robustness, allowing for the creation of high-performance textiles.
Utilizing diisocyanates in polymer manufacturing allows for the tailoring of properties like elasticity, tensile strength, and resistance to wear and tear. Customization of these attributes is based on the selection of different diisocyanates and polyols, varying the resulting material's behavior under different conditions. This chemical adaptability reinforces diisocyanates' pivotal role in developing specialized materials like spandex.