On the basis of the structures presented in this chapter, sketch repeat unit structures for the following polymers: (a) polychlorotrifluoroethylene, and (b) poly(vinyl alcohol).

Polychlorotrifluoroethylene is a polymer known for its chemical resistance and high temperature stability. Understanding its structure begins with identifying its monomer: chlorotrifluoroethylene, which has a molecular formula of C2ClF3.

When drawing the molecular structure, envision a carbon chain where each carbon atom is bonded to chlorine and fluorine atoms. For clarity, here's a simplified representation:
F
|C=C-Cl|F

During polymerization, the C=C double bonds break and form single bonds -C-C-, connecting multiple monomers into a long chain:
[-F
|C-C-Cl
|F-]n

In this formula, 'n' indicates the degree of polymerization, referring to the number of repeating monomer units. This polymer has a notable feature: the alternating chlorine and fluorine atoms attached to the carbon backbone enhance its stability and chemical resilience.

Poly(vinyl alcohol) (PVA) is widely used in various applications, such as textile sizing agents or as support for biodegradable films. It originates from the monomer vinyl alcohol, with the formula C2H4O.

The monomer can be structurally represented as follows:
H
|C=C-O-H
|H

To form PVA, polymers are generated by linking these monomers end-to-end, where the double bonds transform into single bonds within the polymer chain:
[-H
|C-C-O-H
|H-]n

Once again, parameter 'n' denotes the number of repetitive monomers constructed into the polymer chain. PVA's usefulness comes from its solubility in water, biodegradability, and non-toxicity, making it an environmentally friendly material for various industries.

Identifying the monomer units is crucial for understanding polymer chemistry. A monomer is a molecular building block that binds chemically to other monomers to form a polymer chain. To identify a monomer unit, start by looking at the structure of the polymer and finding the smallest segment that repeats throughout.

When examining a polymer:

• Search for patterns in the chain that recur.
• Note any functional groups attached to the main chain, as they are often part of the repeating unit.
• Analyze the molecular formula and check for double bonds that might indicate the point of polymerization.

For instance, chlorotrifluoroethylene and vinyl alcohol are monomers for polychlorotrifluoroethylene and poly(vinyl alcohol), respectively. In both cases, the double bond present in the monomers becomes a single bond in the polymer, reflecting a key point in monomer-polymer transformation.

Representing the structure of a polymer can sometimes be challenging due to its long, repeating chains. The structural formulae of polymers are simplified by focusing on the repeat unit, the smallest section of the chain that illustrates the entire structure.

When depicting polymer structures, simplicity and clarity are important:

• Indicate the repeat unit with square brackets.
• Include any side groups or atoms attached to the main chain.
• Show the points of connection between units, often where double bonds convert to single bonds during polymerization.
• Use the letter 'n' to symbolize the unknown number of repeating units.

By conveying polymers through their repeat units, we create a manageable way to visualize these complex molecules, aiding in the understanding of their properties and the design of new materials.