Problem 63 - Chemistry The Molecular Science

Question

Write the structural formula of four units of the polymer made from the reaction of \(\mathrm{H}_{2} \mathrm{~N}-\left(\mathrm{CH}_{2}\right)_{4}-\mathrm{NH}_{2}\) and \(\mathrm{HOOCCOOH}\). Indicate the repeating unit of the polymer.

Step-by-Step Solution

Answer

The repeating unit is \(-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-\).

Step 1: Understand the reactants

Identify the reactants: 1,4-diaminobutane (\(\mathrm{H}_2\mathrm{~N}-\left(\mathrm{CH}_2\right)_{4}-\mathrm{NH}_2\)) and oxalic acid (\(\mathrm{HOOCCOOH}\)), and understand that a polyamide (nylon) will form.

Step 2: Identify the reaction type

Determine that this reaction is a condensation polymerization where the amine group \(\mathrm{NH}_2\) from 1,4-diaminobutane reacts with the carboxylic acid group \(\mathrm{COOH}\) from oxalic acid, producing water as a byproduct and forming an amide bond (\(-\mathrm{CONH}-\)).

Step 3: Determine the repeating unit

Consider one diacid and one diamine molecule and form the repeating unit: \(-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-\mathrm{CO}-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-\).

Step 4: Write the formula for four units

Combine four repeating units by considering the consecutive amide bond formation: \([-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NH}-\mathrm{CO}-\mathrm{CO}-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-]_4\).

Step 5: Indicate the repeating unit

Highlight the repeating unit in the polymer structure as: \(-\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-\).

Step 6: Finalize the structural formula

Draw four repeating units in sequence and show the continuation bonds to illustrate the polymer structure, indicating the amide linkage between each repeating unit.

Key Concepts

Condensation Polymerization

Condensation polymerization is a basic process used to create complex polymer structures. It involves combining monomers that have two different functional groups. During the reaction, a small molecule, often water, is released. This is important as the removal of the small molecule helps to form the strong covalent bonds that hold the polymer together.
In the case of the reaction we are examining, the monomers involved are 1,4-diaminobutane and oxalic acid. Both monomers have functional groups that play a crucial role in the reaction. The amino group (\(\mathrm{NH}_{2}\)) found in 1,4-diaminobutane and the carboxylic acid group (\(\mathrm{COOH}\)) present in oxalic acid come together, with water as a byproduct. This results in the creation of amide linkages, crucial for the formation of the polymer backbone.
Key points to remember about condensation polymerization include:

• Two different functional groups are involved.
• A small molecule is released, usually water.
• This leads to the formation of a polymer with a repeating pattern of bonds to create a long chain.

Amide Bond

Amide bonds are an essential chemical link in the formation of polyamide polymers, like nylons. They form when an amino group (\(\mathrm{NH}_{2}\)) reacts with a carboxylic acid group (\(\mathrm{COOH}\)). This type of bond is notable for its strength and stability, making it suitable for materials that require durability.
The amide bond formation is a key step in our specific reaction, as the amide linkage (\(\mathrm{-CONH_2-}\)) provides the primary connection between repeating units in the polymer chain. When considering the reaction between 1,4-diaminobutane and oxalic acid, the formation of the amide bond happens repeatedly, driving the growth of the polymer chain.
The characteristics of an amide bond include:

• Formation through a condensation reaction, typically releasing water.
• Stable and strong connection ideal for polymers.
• A characteristic linkage of polyamide polymers.

Understanding the nature of amide bonds helps in appreciating why polymers like nylons are used so widely in textiles and mechanical applications.

Repeating Unit

The repeating unit is the basic building block of a polymer chain. It's formed from the monomers used in the polymerization process and repeats continuously to make up the long chain structure of the polymer.
For the polymer made from 1,4-diaminobutane and oxalic acid, the main repeating unit is characterized by the linking of \(\mathrm{NH}-(\mathrm{CH}_2)_4-\mathrm{NHCO}-\). This repeating unit represents the essential structure that repeats throughout the polyamide chain.
The repeating unit is important because it determines the properties of the polymer, including its chemical and mechanical behavior. The repeating unit can influence factors like flexibility, temperature resistance, and strength, making it crucial in designing materials for specific applications.
Key aspects of understanding repeating units include:

• It is derived from the monomers.
• The chemical structure repeats to form a long chain.
• Understanding this helps define the polymer's properties.

Through the repetition of these units, durable materials like nylons are formed, which have extensive applications in multiple fields, from fashion to industrial materials, due to their resilience and versatility.