Question

Write the structural formulas of the monomers of each of the following polymers, for which one repeating unit is shown: (a) polyvinylchloride \((\mathrm{PVC}),-\left(\mathrm{CHClCH}_{2}\right)_{n}-\); (b) Kel-F, \(-\left(\mathrm{CFClCF}_{2}\right)_{n}-\).

Short answer

The monomers are (a) vinyl chloride or chloroethene \( (CH_2=CHCl) \) for PVC, and (b) 1,1-dichloro-2,2-difluoroethylene \( (CF_2=CFCl) \) for Kel-F.

Step-by-step solution

Identify Monomer Structure for PVC

Examine the repeating unit of polyvinylchloride (PVC), which is \( -(\text{CHClCH}_2)_{n}- \). The monomer must be the smallest unit that can be repeated to form this polymer. Remove one repetition to find the monomer, which is vinyl chloride or chloroethene, structured as \( \text{CH}_2=CHCl \).

Identify Monomer Structure for Kel-F

Observe the repeating unit of Kel-F, which is \( -(\text{CFClCF}_2)_{n}- \). To find the monomer, consider a single repeat and modify the unit to reflect a double bond necessary for polymerization. The monomer is 1,1-dichloro-2,2-difluoroethylene, with the structure \( \text{CF}_2=CFCl \).

Key concepts

Polymer Chemistry

Polymer chemistry underpins much of materials science, as it involves the study and manipulation of macromolecules composed of repeating structural units, namely monomers. These monomers are small molecules that can join together to form long chains or networks, creating polymers with diverse properties. The process of forming polymers from monomers is called polymerization.

There are two main types of polymerization: addition polymerization and condensation polymerization. Addition polymerization involves monomers adding to one another without the loss of atoms from the monomers, which is the case for polymers like polyvinylchloride (PVC). In condensation polymerization, two monomers react together with the elimination of a small molecule, such as water or HCl.

Understanding the molecular structure and chemical behavior of the monomers is crucial because it determines the final characteristics of the polymer. For instance, the introduction of different atoms or functional groups can impart the polymer with unique physical and chemical properties, such as flexibility, chemical resistance, or thermal stability.

Polyvinylchloride (PVC)

Polyvinylchloride, commonly referred to as PVC, is a widely used thermoplastic polymer. Its fame stems from its versatility, durability, and economy. PVC is produced from the monomer vinyl chloride, or chloroethene, which features a vinyl group that is critical for the polymerization process.

The continuous repeating unit of PVC, represented as \(-(\text{CHClCH}_2)_n-\), highlights the alternate arrangement of a chlorinated carbon with a methylene group. This structural aspect explains the properties of PVC has, such as its good insulation properties and chemical resistance. PVC is massively used in construction for pipes, vinyl flooring, and window frames, as well as in healthcare for medical devices and tubing. The chlorine atom in the polymer backbone gives PVC its flame-retardant properties, enhancing its value in various industries.

Monomer Identification

Identifying the monomers from which polymers are synthesized is a foundational skill in polymer chemistry and material science. To uncover the monomers, one must examine the structural formula of a given polymer and deduce the smallest unit that can repetitively link to form the polymer chain.

For example, in polyvinylchloride (PVC), the repeating unit is \(-(\text{CHClCH}_2)_n-\). By recognizing this pattern, the monomer can be determined to be vinyl chloride, or chloroethene, with the formula \(\text{CH}_2=CHCl\). This deduction process typically requires the addition of double bonds to the repeating unit to account for the monomers before they have been polymerized. The critical step in monomer identification is to simplify the polymer to the simplest repeat unit and then applying knowledge of bonding and chemical reactions to identify the monomer's original structure.

Kel-F Polymer

Kel-F polymer, also known as polychlorotrifluoroethylene, is another type of polymer with useful applications, especially where chemical resistance and thermal stability are required. The monomer of Kel-F is identified by examining its repeating unit \(-(\text{CFClCF}_2)_n-\) and predicting the original monomer structure before polymerization.

The monomer is 1,1-dichloro-2,2-difluoroethylene, with the formula \(\text{CF}_2=CFCl\). Kel-F's chemical composition includes both chlorine and fluorine, which contribute to the polymer's non-reactive nature against most chemicals and solvents. As such, Kel-F is particularly valued in the chemical industry for making gaskets, seals, and other components that must withstand aggressive chemicals and high temperatures. Understanding the structure of the Kel-F monomer helps to anticipate the properties of the final polymer, facilitating the development of advanced materials tailored for specific applications.