Question

Which one of the following pairs of monomers is used in the manufacture of 'Dacron'? (a) acrylonitrile and vinyl acetate (b) tetephthalic acid and ethylene glycol (c) phthalic acid and ethylene glycol (d) adipic acid and hexamethylene diamine

Short answer

The pair of monomers used to manufacture Dacron is (b) terephthalic acid and ethylene glycol.

Step-by-step solution

Understand the Context

Dacron is a type of polyester fabric. It is important to recognize that polyester is a polymer made by the reaction of a diacid and a diol (an alcohol with two hydroxyl groups). Identifying substances that match this description is key.

Examine the Options

Look closely at each option, identifying which options include the combination of a diacid and a diol suitable for creating a polyester polymer, such as Dacron.

Assess Dacron Monomer Requirements

Dacron is specifically known to be made from the polymerization of terephthalic acid (a diacid) and ethylene glycol (a diol). These substances react to form polyethylene terephthalate (PET), which is Dacron.

Identify the Correct Pair

From our understanding in step 3, option (b) "tetra phthalic acid and ethylene glycol" is the correct combination used in making Dacron, since it results in the formation of the PET polymer.

Key concepts

Polymerization

Polymerization is a chemical process that helps create large molecules called polymers by connecting smaller molecules known as monomers. Imagine constructing a chain where each link is a monomer and the entire chain represents a polymer. There are different types of polymerization, but when making polyester, we normally rely on a specific type called condensation polymerization.
In condensation polymerization, the monomers join together, resulting in the formation of small by-products, often water or methanol. This is different from addition polymerization, where no by-products are made. Condensation polymerization forms strong and durable polymers like polyester.

• Step 1: The monomers come together, typically through the reaction between a diacid (a molecule with two acid groups) and a diol (a molecule with two alcohol groups).
• Step 2: As these molecules react, they release a small molecule by-product, frequently water, which is why it's called condensation polymerization.
• Step 3: The reaction continues until long chains of polymers are created.

These processes allow industries to create materials like polyester, which is adaptable for various uses, from clothing to bottles.

Terephthalic Acid

Terephthalic acid is an organic compound and acts as one of the key monomers in the production of polyester such as Dacron. Chemically, it is known as a diacid, indicating it has two acid groups. This feature makes it ideal for forming long chains during polymerization.

Terephthalic acid is represented by the formula C₆H₄(COOH)₂, highlighting its two carboxylic acid groups. In the creation of polyester, these acid groups react with alcohol groups found in diols like ethylene glycol. This reaction is crucial in forming the backbone structure of polyester.

• Key Feature 1: It provides the acid groups necessary for condensation reactions.
• Key Feature 2: Its structure contributes to the rigidity and durability of the resulting polymer chains.
• Uses: Essential in the manufacture of not only fibers like Dacron, but also bottles, films, and more.

The importance of terephthalic acid cannot be overstated, as it is the starting point for creating the robust characteristics found in polyester products.

Ethylene Glycol

Ethylene glycol stands out as a diol used prominently in the formation of polyester via polymerization. A diol means it has two hydroxyl (OH) groups capable of reacting with acids such as those in terephthalic acid. This reaction is fundamental for creating polyesters like Dacron.

Chemically, ethylene glycol is expressed as C₂H₄(OH)₂. Its role is to react with the acid groups in the reaction, aiding in building long chains of polymers.
The properties of ethylene glycol include its ability to lower the freezing point of water, making it useful in various applications beyond polyester. However, in polymer sciences, its dual alcohol groups are key to forming durable polymers.

• Main Use: It helps combine with acids to form the ester linkages that hold polyester chains together.
• Additional Use: It's a crucial part in other chemical processes due to its antifreeze capabilities and solvent properties.

Ethylene glycol is versatile not only in industrial applications but also as a building block for fabrics and materials we use daily.