Question

Polymerization of 2-chloro-1,3-butadiene under Ziegler-Natta conditions gives a synthetic elastomer called neoprene. All carbon-carbon double bonds in the polymer chain have the trans configuration. Draw the repeat unit in neoprene.

Short answer

Answer: The repeat unit of neoprene is -CH2-CH=CH-CH2-Cl- with the carbon-carbon double bond in the trans configuration.

Step-by-step solution

Identify the monomer structure

First, let's determine the structure of the monomer, 2-chloro-1,3-butadiene. It has four carbon atoms, one being bonded to a chlorine atom, and two carbon-carbon double bonds. The structure of 2-chloro-1,3-butadiene is: H2C=CH-CH=CH-Cl

Ziegler-Natta polymerization

The Ziegler-Natta polymerization process facilitates the formation of polymers with specific stereochemistry. In the case of neoprene, Ziegler-Natta polymerization leads to the formation of carbon-carbon double bonds in the trans configuration.

Draw the repeat unit

Now we need to draw the repeat unit of neoprene. During the polymerization process, the double bonds in 2-chloro-1,3-butadiene react and form single bonds between each monomer unit, resulting in the following repeat unit: -CH2-CH=CH-CH2-Cl- Notice that the carbon-carbon double bond in the repeat unit has the trans configuration, as mentioned in the problem. This is the repeat unit of neoprene.

Key concepts

Neoprene

Neoprene is a synthetic rubber that is derived from the polymerization of 2-chloro-1,3-butadiene. It is known for its excellent chemical stability and resistance to weathering, oils, and heat. This makes it a popular choice for manufacturing a variety of products like wetsuits, laptop sleeves, and orthopedic braces.

In the lab, neoprene is created using Ziegler-Natta polymerization, a process which ensures that the polymer chains have a consistent arrangement of molecules. This helps deliver the desirable properties that neoprene is known for. When processed correctly, neoprene can be quite flexible yet robust, making it ideal for applications that require both strength and flexibility.

The unique properties of neoprene are closely linked to its structural aspects, specifically how the carbon-carbon double bonds are arranged in the polymer chain. This brings us to the next concept, an arrangement known as the trans configuration.

Trans Configuration

The concept of configuration refers to the geometric arrangement of atoms within a molecule. In the case of carbon-carbon double bonds, two main configurations exist: cis and trans.

In a trans configuration, the substituents (or groups) attached to the carbon atoms of the double bond are placed on opposite sides. Imagine it like a straightened bridge, offering more stability and rigidity compared to the bending or folding present in a cis configuration.

This characteristic trans pattern is what we observe in the polymer chains of neoprene, thanks to the Ziegler-Natta polymerization process.

• It influences the polymer's physical properties like strength and elasticity.
• Makes the material resistant to environmental factors.

The stability associated with the trans configuration is a key reason that neoprene has become such a reliable material in various demanding applications.

2-Chloro-1,3-butadiene

Understanding 2-chloro-1,3-butadiene is critical, as it serves as the monomer for creating neoprene. This compound is the starting point in the polymerization process and its structural features significantly impact the resulting polymer.

Chemically, 2-chloro-1,3-butadiene consists of four carbon atoms. Two of these carbons feature double bonds, which are essential for the polymer forming reaction and the final characteristics of neoprene.

Additionally, one of the carbons is bonded to a chlorine atom. This chlorine not only plays a role in the polymerization process but also influences the chemical stability and reactivity of neoprene.

• The double bonds contribute to the formation of long, flexible polymer chains.
• The chlorine atom aids in enhancing certain mechanical and chemical properties.

Hence, the intrinsic chemical details of 2-chloro-1,3-butadiene are pivotal in shaping the unique qualities of neoprene, making the connection between molecular structures and material properties clearer.