Problem 105 - Chemistry The Science in Context

Question

Draw the carbon-skeleton structure of the condensation polymer of \(\mathrm{H}_{2} \mathrm{N}\left(\mathrm{CH}_{2}\right)_{6} \mathrm{COOH} .\) How does this polymer compare with nylon- \(6 ?\)

Step-by-Step Solution

Answer

Answer: The main structural difference between the condensation polymer formed from the given monomer and nylon-6 is the number of methylene (-CH2-) groups between the amide bonds. The condensation polymer has six methylene groups, while nylon-6 has only five.

Step 1: Understanding condensation polymerization

Condensation polymerization is a type of polymerization reaction where monomers combine with the loss of a small molecule (such as water). In this exercise, the given monomer is \(\mathrm{H}_{2} \mathrm{N}\left(\mathrm{CH}_{2}\right)_{6} \mathrm{COOH}\). Given that it contains a primary amine (-NH2) group and a carboxylic acid (-COOH) group, condensation polymerization will involve forming an amide bond between the two groups with the loss of a water molecule.

Step 2: Drawing the carbon-skeleton structure of the polymer

To draw the carbon-skeleton structure of the condensation polymer, we will first examine the given monomer. It can be represented as: \(\mathrm{H}_{2}\mathrm{N}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{COOH}\) Now, let's consider how the condensation polymerization would occur for this monomer. A water molecule will be removed as the -NH2 group from one monomer reacts with the -COOH group of another monomer. This forms an amide bond (-CO-NH-) between the two monomers: Monomer 1: \(\mathrm{H}_{2}\mathrm{N}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{COOH}\) Monomer 2: \(\mathrm{H}_{2}\mathrm{N}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{COOH}\) Polymer after condensation: \(\mathrm{H}_{2}\mathrm{N}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CONH}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{COOH}\) This process repeats, and the condensation polymer formed is: \([ -\mathrm{NH}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}- ]_{n}\) → the carbon-skeleton structure of the condensation polymer.

Step 3: Comparing with nylon-6

Nylon-6 is a type of polyamide made by the ring-opening polymerization of caprolactam. The chemical structure of nylon-6 is: \([ -\mathrm{NH}-\left(\mathrm{CH}_{2}\right)_{5}-\mathrm{CO}- ]_{n}\) Comparing the carbon-skeleton structure of the condensation polymer formed in this exercise with that of nylon-6, we can see the difference in the number of methylene (-CH2-) groups. The condensation polymer has six methylene groups between the amide bonds, whereas nylon-6 has only five. In summary, the carbon-skeleton structure of the condensation polymer formed from the given monomer is \([ -\mathrm{NH}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}- ]_{n}\). It is similar to nylon-6 but has an extra methylene group in the polymer chain.

Key Concepts

Amide Bond

An amide bond, also known as a peptide bond, is a key feature in many organic and biological compounds. This bond forms between a carboxylic acid group and an amine group. The reaction typically involves the removal of a water molecule, hence the term 'condensation reaction'. This phenomenon can be specifically represented in polymer chemistry, where monomers such as

• Primary amines (-NH extsubscript{2})
• Carboxylic acids (-COOH)

combine to form long chains. The amide bond acts as a connector linking these smaller molecules into large, functional strands.

In the case of forming the condensation polymer from the monomer ewline extlessbr extend ewline H extsubscript{2}N-(CH extsubscript{2}) extsuperscript{6}-COOH, the amide bond (-CO-NH-) is the result of this condensation reaction, crucially establishing the backbone of the polymer chain.

Nylon-6

Nylon-6 is a synthetic polyamide, renowned for its durability and resistance to wear. It is created through the polymerization of caprolactam. This process is a bit different from typical condensation polymerization since it involves ring-opening polymerization.

The repeating unit of nylon-6 is:

• (-NH-(CH extsubscript{2}) extsubscript{5}-CO-)

One can note the use of six carbon atoms, which gives it the name nylon-6. But, unlike typical condensation polymers, nylon-6 has slightly different structural properties because of its manufacturing process, which influences its physical properties like toughness and elasticity. It is widely used in making textiles, carpets, and industrial threads.

Polymer Structure

The polymer structure is essentially the arrangement of repeating units, known as monomers, in a long chain. This can vary greatly between different polymers, affecting the properties and uses of the material.

In condensation polymers like those formed by the monomer H extsubscript{2}N-(CH extsubscript{2}) extend{6}-COOH, the polymer structure includes long, repeating sequences of atoms connected by amide bonds. The structure is essentially represented by repeating chemical shorthand like:

• (-NH-(CH extsubscript{2}) extsubscript{6}-CO-)

Each segment of this sequence reflects a unit of polymer formed from one monomer, minus the elements lost in the condensation process (typically a water molecule). The specific sequence pattern and number of repetitions ( ) define the polymer characteristics.

Carbon-Skeleton Structure

The carbon-skeleton structure is a simplified representation of a compound showing primarily the carbon atoms. For polymers, especially those formed via condensation reactions, this helps in recognizing the long chain of repeating units.

In our example, the carbon-skeleton structure of the polymer made from

• H extsubscript{2}N-(CH extsubscript{2}) extsubscript{6}-COOH

is displayed as:

• (-NH-(CH extsubscript{2}) extsubscript{6}-CO-) extsubscript{n}

Understanding this skeleton provides a basis to compare different polymers by their chain length and structure. Here, each monomer adds a segment with 6 methylene (-CH extsubscript{2}-) units, which is notable when comparing with nylon-6, which only has 5 methylene units within its carbon skeleton structure. Such differences influence the physical and chemical behaviors of the resulting polymers.