Problem 109 - Chemistry The Science in Context

Question

Superglue The active ingredient in superglue is methyl 2-cyanoacrylate (Figure P12.109). The liquid glue hardens rapidly when methyl 2 -cyanoacrylate polymerizes. This happens when it contacts a surface containing traces of water or other compounds containing - OH or - NHgroups. Draw the carbon- skeleton structure of two repeating monomer units of poly(methyl 2-cyanoacrylate).

Step-by-Step Solution

Answer

Question: Draw the carbon-skeleton structure of two repeating monomer units of poly(methyl 2-cyanoacrylate), the active ingredient in superglue. Answer: H2C-C(CN)COOCH3-HC-C(CN)COOCH3-H

Step 1: Draw the structure of methyl 2-cyanoacrylate monomer

Firstly, we need to draw the structure of the monomer, methyl 2-cyanoacrylate. The structure is as follows: H2C=C(CN)COOCH3 The monomer contains a carbon-carbon double bond, a cyano group (CN), an ester group (COOCH3), and two hydrogen atoms attached to the first carbon.

Step 2: Repeat the monomer twice to draw two repeating units

Now, we will repeat the monomer twice to represent two repeating units. When polymerization occurs, the carbon-carbon double bond opens, and the two monomers connect. The structure after polymerization becomes: H2C-C(CN)COOCH3-HC-C(CN)COOCH3-H Notice that the carbon-carbon double bond within the monomer units has now become a single bond, and the two repeating units are connected via a single bond between their respective carbons previously involved in the double bond.

Key Concepts

Methyl 2-Cyanoacrylate

Methyl 2-cyanoacrylate is the primary component in many quick-setting adhesives, notably known as superglue. It is a colorless liquid that rapidly transforms into a solid through a chemical process called polymerization.
Upon contact with moisture, such as water present on surfaces, it polymerizes to form strong, durable adhesive bonds.

• Its chemical formula is represented as H extsubscript{2}C=C(CN)COOCH extsubscript{3}.
• Key characteristic components include a cyano group, an ester group, and a double bond which is crucial for initiation of the polymerization process.

This ability to quickly form bonds makes it widely used for fast adhesive applications in both household and industrial settings.

Monomer Structure

The structure of a monomer is the fundamental building block of polymers. In methyl 2-cyanoacrylate, the monomer structure is unique because it facilitates rapid polymerization.
The monomer has several key components, contributing to its reactivity:

• A carbon-carbon double bond that is pivotal in initiating the polymerization.
• A cyano group, which influences the monomer's properties such as polarity and reactivity.
• An ester group (COOCH extsubscript{3}), which affects solubility and bonding characteristics of the polymer.

Understanding the configuration of these components in the monomer helps in recognizing its tendency to form long polymer chains.

Carbon-Carbon Double Bond

At the heart of polymerization of methyl 2-cyanoacrylate lies the carbon-carbon double bond. It is represented as C=C within the monomer structure and is crucial because it is the site of chemical reactions during polymer formation.
When polymerization is initiated:

• The double bond opens up, allowing the monomers to attach to one another.
• This results in the formation of single carbon-carbon bonds, linking the monomers into a long chain.
• The strong adhesion properties are a result of this bond rearrangement as it changes the substance from a liquid to a solid.

This transformation highlights the reactivity and versatility of carbon-carbon double bonds in synthetic chemistry.

Cyano Group

The cyano group (CN) in methyl 2-cyanoacrylate plays a crucial role in both its chemical properties and application. This group consists of a carbon triple-bonded to a nitrogen atom, adding distinctive characteristics to the molecule.
It influences the following aspects of the monomer:

• Electrophilicity - making the compound more reactive and ready for polymerization.
• Polarity - contributing to the molecule's positive interaction with polar materials like water.
• The strength and rigidity of the resultant polymer due to its inherent stability and structural reinforcement.

Understanding these effects helps to explain why cyanoacrylate adhesives are strong and fast-acting upon exposure to moisture.