Problem 87 - Chemistry: The Central Science in SI Units, Global Edition

Question

An addition polymerization forms the polymer originally used as Saran" wrap. It has the following structure \(\mathrm{t} \mathrm{CCl}_{2}-\mathrm{CH}_{2}+_{n}\). Draw the structure of the monomer.

Step-by-Step Solution

Answer

The monomer structure for the given addition polymer is \(\mathrm{tCCl}_{2} = \mathrm{CH}_{2}\) and can be drawn as: ``` Cl | C = C - H | Cl ```

Step 1: Identifying the repeating units

To identify the monomer, we first need to recognize the repeating units in the given polymer. The structure is given as \(\mathrm{tCCl}_{2} - \mathrm{CH}_{2} +_{n}\), notice that the \(\mathrm{tCCl}_{2}\) and the \(\mathrm{CH}_{2}\) are connected and form the repeating units in the polymer chain.

Step 2: Determining the monomer structure

The repeating unit in the polymer consists of \(\mathrm{tCCl}_{2}\) and \(\mathrm{CH}_{2}\). As it is an addition polymer, these two units must combine without the loss of any atoms or molecules. Therefore, the double bond between the carbon and chlorine atoms in \(\mathrm{tCCl}_{2}\) will break to form a single bond, which will then connect with the \(\mathrm{CH}_{2}\) unit. The leftover bond from the \(\mathrm{tCCl}_{2}\) will be used to create a double bond with the carbon atom in the \(\mathrm{CH}_{2}\) unit. Hence, the structure of the monomer will be \(\mathrm{tCCl}_{2} = \mathrm{CH}_2\).

Step 3: Drawing the monomer structure

The structure of the monomer can now be drawn as follows: ``` Cl | C = C - H | Cl ``` So, the final structure of the monomer is \(\mathrm{tCCl}_{2} = \mathrm{CH}_{2}\).

Key Concepts

Monomer Structure

Monomer structure is an essential concept in polymer chemistry. When we talk about **monomers**, we mean the building blocks used to form polymer chains.
Understanding how they connect is key to forming polymers like those found in Saran wrap. Let's break it down further.

In the context of the addition polymerization for Saran wrap, the monomer structure is represented as \(\text{CCl}_2 = \text{CH}_2\). Here's how it works:

• Each monomer consists of a specific arrangement of atoms, in this case, two carbon atoms double-bonded to each other.
• Attached to one of these carbon atoms, we find two chlorine atoms (\(\text{CCl}_2\)).
• On the other side, a hydrogen atom (\(\text{CH}_2\)) is connected to the second carbon atom.

When these monomers undergo polymerization, the carbon-carbon double bonds break. This allows the monomers to link together, forming long chains which are a hallmark of polymer structures. Recognizing and drawing the monomer accurately is crucial for visualizing how polymers like Saran wrap are built.

Saran Wrap Polymer

Saran wrap is an iconic product made of a particular type of polymer, known as **polyvinylidene chloride** (PVDC). Understanding this polymer requires exploring its structure and properties.

Here are some key points:

• Saran wrap is created through addition polymerization, a process that forms polymers without losing any smaller molecules. It results in high-strength materials ideal for wrapping and sealing food.
• The repeating unit in the Saran wrap polymer is derived from the monomer \(\text{CCl}_2 = \text{CH}_2\), indicative of vinylidene chloride. This monomer is added repeatedly to create a chain.
• PVDC, being a dense and impermeable polymer, provides excellent resistance against water vapor and gases, keeping food fresh for longer.
• Its unique arrangement of carbon, chlorine, and hydrogen atoms contributes to its characteristics, such as clarity, adherence, and tensile strength.

By understanding the chemistry behind Saran wrap, we appreciate its everyday practicality fueled by scientific innovation.

Repeating Units in Polymers

Repeating units are the backbone of any polymer chain. In simple terms, these are the **sections that repeat** over and over to form the entire polymer chain. They are derived from monomers and are essential for understanding polymer composition.

For Saran wrap, the repeating unit is formed from the monomer \(\text{CCl}_2 = \text{CH}_2\). Here's how repeating units contribute:

• Each time the monomer joins the polymer chain, it contributes a small section known as a **repeating unit**.
• In Saran wrap, this repeating unit adds both carbon and chlorine atoms to the chain, giving the polymer its characteristic properties.
• The more units are repeated, the longer the polymer becomes, which affects its mechanical properties like strength and elasticity.

The concept of repeating units is central to synthetic chemistry, as it determines the properties and functionality of the polymer materials we use every day. By mapping the repeating units back to their monomer origins, we gain insight into both the polymer's formation and its useful properties.