Problem 110 - Chemistry: The Central Science

Question

Teflon is a polymer formed by the polymerization of \(\mathrm{F}_{2} \mathrm{C}=\mathrm{CF}_{2}\) - (a) Draw the structure of a section of this polymer. (b) What type of polymerization reaction is required to form Teflon?

Step-by-Step Solution

Answer

A section of the Teflon polymer can be represented as: ... -[ -F2C-CF2- ]n- ..., with the units repeating n times. Teflon is formed through a chain-growth (addition) polymerization reaction, where the carbon-carbon double bond in the monomer opens up and bonds to another monomer without producing any additional small molecules.

Step 1: Understanding the Teflon monomer

The Teflon monomer, F2C=CF2, has a carbon-carbon double bond (C=C) and is bonded to two fluorine atoms (F) at each carbon atom. The structure of the monomer can be drawn like this: F F | | -C=C- | | F F

Step 2: Drawing a section of the Teflon polymer

To draw a section of the Teflon polymer, we need to understand how the monomer units link together. In this case, the carbon-carbon double bond in the monomer will open up and bond to another monomer. To visualize this, imagine the Teflon monomer units connecting at the carbon atoms, with the carbon-carbon double bond now becoming a single bond. We can represent the repeating unit of the Teflon polymer with parentheses and an "n" in subscript to show that the structure repeats multiple times. So, a segment of the Teflon polymer will look like this: ... -[ -F2C-CF2- ]n- ... ... with the units repeating n times.

Step 3: Identify the type of polymerization reaction

There are two main types of polymerization reactions: chain-growth (addition) and step-growth (condensation). In a chain-growth polymerization, the reaction occurs through the opening of a double bond where a monomer unit keeps adding to the active site of the growing polymer chain. In a step-growth polymerization, two monomer units react with each other, forming a new bond and a small byproduct molecule. Since the Teflon monomer units link together through the reaction of the carbon-carbon double bond, and do not produce any additional small molecules, we can conclude that Teflon is formed by a chain-growth (addition) polymerization reaction.

Key Concepts

Chain-Growth Polymerization

Chain-growth polymerization is a fundamental process used to form many polymers, including Teflon. In this method, the polymer grows by adding one monomer at a time to the active site of a growing chain. Unlike step-growth polymerization, where two monomer molecules react to form a bond, chain-growth uses the energy stored in double bonds to link monomers together.
For Teflon, each monomer is the molecule \(\mathrm{F}_2\mathrm{C}=\mathrm{CF}_2\). The polymerization process begins with breaking the carbon-carbon double bond. This reaction occurs under specific conditions that enable the monomers to join at the newly formed active sites.

• Monomers add in a sequence, creating long, repeating chains.
• The nature of the reaction means no by-products are formed.
• This process allows for the creation of high molecular weight polymers quickly.

The simplicity of adding monomers makes chain-growth polymerization efficient for industrial production of polymers like Teflon.

Addition Reactions

An addition reaction is vital in the context of chain-growth polymerization. This chemical process involves opening a double bond within a monomer so it can join with another monomer. In Teflon's case, the reaction is quite straightforward. The double bonds are broken, allowing a new single bond to form between each carbon atom of adjacent monomers.
The nature of addition reactions provides several advantages:

• There are no waste products, making the reaction clean and efficient.
• The process readily forms a continuous network, perfect for creating strong, durable polymers.
• This type of reaction is fast, often requiring only a catalyst to initiate.

Addition reactions are foundational for many industrial polymers, not just Teflon, creating everything from plastics to synthetic rubbers.

Polymer Structure

The structure of a polymer like Teflon is determined by the way its monomers are arranged. In Teflon, the polymer chain is composed of repeating units of the formula \(\text{-[F}_2\text{C-CF}_2\text{]}_n\text{-}\). These units form a stable, linear chain.
Several aspects define its structure:

• Each carbon atom is bonded to two fluorine atoms, providing exceptional chemical resistance.
• The linear arrangement of atoms results in a non-stick surface, which is a hallmark of Teflon.
• The consistent, repeating pattern enhances strength and resilience, making Teflon an excellent choice for applications requiring durability.

The specific arrangement of atoms in Teflon's polymer structure is what gives it its unique properties, distinguishing it from other types of plastics.