Problem 57 - Chemistry in Focus

Question

Give the structure of the monomer from which the following addition polymer is formed: \(-\mathrm{CH}_{2} \mathrm{CHCNCH}_{2} \mathrm{CHCNCH}_{2} \mathrm{CHCN}-\)

Step-by-Step Solution

Answer

The structure of the monomer is \(\mathrm{CH}_{2}=\mathrm{C}(\mathrm{CN})H\).

Step 1: Understand the Polymer Structure

Examine the given polymer chain and look for repeating units. These repeating units are often enclosed in parentheses or brackets and followed by a subscript n, indicating how many times they are repeated. In this case, the repeating unit is not explicitly enclosed, but can be deduced by identifying the pattern within the chain.

Step 2: Identify the Repeating Unit

Look for the smallest repeating element in the chain that could represent a monomer. For the given polymer, we can identify that the repeating unit is \(\mathrm{CH}_{2}\mathrm{CHCN}\) as this segment repeats through the length of the polymer.

Step 3: Determine the Monomer Structure

Reconstruct the monomer by taking the identified repeating unit and adding double bonds where necessary to account for valency and bonding before the polymerization process. As the polymer is formed by an addition reaction, the double bond will be between the two carbon atoms: \(\mathrm{CH}_{2}=\mathrm{C}(\mathrm{CN})H\), which is the structure of the monomer.

Key Concepts

Polymer Chemistry Explained

Polymer chemistry is a fascinating and complex field that deals with the study and manipulation of polymers, which are large molecules made up of repeating structural units called monomers. These monomers are the building blocks of polymers and can be thought of as beads on a string, where the string represents the polymer itself. The process by which monomers combine to form polymers is known as polymerization, and there are two main types: addition polymerization and condensation polymerization.

In addition polymerization, monomers add to each other without the loss of any atoms, whereas in condensation polymerization, monomers join together with the loss of small molecules, often water. Understanding the types of polymerization is crucial for identifying the structure of monomers that create different polymers.

Identifying Repeating Units in Polymers

Polymers owe their unique properties to their structure, which is composed of repeating units derived from monomers. When analyzing a polymer, finding these repeating units helps reveal the monomer's original structure. These units can manifest as patterns within the polymer chain, typically replicated over the entire length or a significant portion of the molecule.

Recognizing these patterns allows chemists to reverse-engineer the polymer's construction process, a method that plays a significant role in fields like materials science and forensic analysis. Understanding and identifying these repeating units is not only key to characterizing the polymer but also essential in designing new polymers with specific desired properties.

Monomer Identification Techniques

To identify the monomer from a polymer structure, chemists use knowledge of chemical bonding and organic structures. In the case of addition polymers, this process involves pinpointing the repeating unit and then applying a bit of reverse chemistry. Since addition polymers are formed without the loss of any atoms, the monomer must contain the same atoms as the repeating unit but arranged with unsaturation to allow for the polymerization reaction.

A skillful chemist looks for the presence of a double bond in the monomer, permitting it to open up and link with other monomers to create the polymer chain. By understanding how the bonds arrange during polymerization, it's possible to elucidate the monomer's molecular structure. This reconstruction is akin to solving a puzzle, ensuring that all atoms have a complete valence and the resulting structure is chemically stable and likely to undergo polymerization.