Problem 63 - Chemistry Principles and Practice

Question

Viton is a strong, flexible chain-growth copolymer used in gaskets. It is formed from 1,1 -difluoroethylene and hexafluoropropene. Draw the repeating unit.

Step-by-Step Solution

Answer

The repeating unit of Viton is -[CH2-CF2-CH(CF3)]-.

Step 1: Understand the monomers

Viton is synthesized from two specific monomers: 1,1-difluoroethylene (C2H2F2) and hexafluoropropene (C3HF6). These are the building blocks that repeat throughout the polymer chain.

Step 2: Determine the structure of 1,1-difluoroethylene

Analyze the structure of 1,1-difluoroethylene. It consists of a carbon-carbon double bond where each carbon is bonded to one hydrogen atom and one fluorine atom, represented as CH2=CF2.

Step 3: Determine the structure of hexafluoropropene

Hexafluoropropene consists of a carbon-carbon double bond as well, with a terminal fluoromethyl group. Its chemical formula is CF3-CF=CF2, indicating two carbons bonded to fluorine atoms.

Step 4: Combine the monomers into a repeating unit

To create the repeating unit, alternate the monomers. The combination might look like this: ...-CH2-CF2-CH(CF3)-CF2-..., suggesting CR-CR' components are adjacent linkages.

Step 5: Represent the repeating unit visually

Draw the structure, showing a bond between the two monomer units to form the polymer chain. This might resemble -[CH2-CF2-CH(CF3)]- as the repeating unit.

Key Concepts

Viton

Viton is a well-known copolymer used extensively for its robust and versatile properties. It is specifically engineered to resist heat, chemicals, and extreme weather conditions. This makes it a perfect choice for applications like seals and gaskets.
Viton's unique attributes come from its composition, which includes monomers like 1,1-difluoroethylene and hexafluoropropene. These monomers provide the material with superior flexibility and durability, making Viton polymers reliable for use in demanding environments.
Some notable characteristics of Viton include:

• High temperature resistance
• Exceptional chemical stability
• Resistance to oils and contaminants
• Elasticity and strength

These attributes arise from its polymer structure, derived from the repetitive monomer units.

Monomers

Monomers are the fundamental building blocks of polymers. In the case of Viton, it is made up of two primary monomers: 1,1-difluoroethylene (C2H2F2) and hexafluoropropene (C3HF6).
These monomers each have a unique structure that contributes to the properties of the final copolymer, Viton.
1,1-Difluoroethylene consists of:

• A double bond between two carbon atoms
• Each carbon bonded to one hydrogen atom
• Each carbon bonded to one fluorine atom

Hexafluoropropene is built with:

• A double bond between the central carbon atoms
• Two of these carbons attached to fluorine atoms
• A fluoromethyl group at one end

These monomers, through a chemical process, link together to form long chains, resulting in a repeated pattern that defines the polymer structure.

Repeating Unit

The repeating unit is the basic element that, when linked in succession, forms the entire polymer chain. For Viton, the repeating unit comes from the combination of its two monomers: 1,1-difluoroethylene and hexafluoropropene.
This alternating structure can be visualized as follows:

• CH2-CF2 from 1,1-difluoroethylene
• CH(CF3)-CF2 from hexafluoropropene

The resulting structure of the repeating unit in Viton is typically written as:
\[-[CH2-CF2-CH(CF3)]-\]
This pattern repeats many times, depending on the copolymer's desired length and characteristics.
The repeating unit's design enables Viton to maintain its superior structural stability and flexibility under pressure.

Polymer Structure

Understanding the polymer structure of Viton involves comprehending how its repeated units are organized to form the complete copolymer.
The polymer structure results from the systematic alignment of the monomers, where each repeating unit is linked by covalent bonds.
The structure of a polymer can be linear, branched, or cross-linked, affecting its properties like melting point and solubility. In the case of Viton, its chain-growth polymerization follows a linear pattern which contributes to its elasticity and resilience.
Within the polymer's architecture:

• Covalent bonds ensure chain integrity and strength
• The sequence of repeating units creates a stable structure
• The arrangement of polar and nonpolar segments influences its chemical resistance

Understanding these structural details helps clarify why Viton is chosen for high-performance applications like gaskets.