Animated Solution for Chemistry - Polymers: Which of the following is a thermosetting polymer?

A Structural Perspective

When we dive into the fascinating world of polymers, one of the most crucial ways to classify them is based on their molecular structure and how they respond to heat. Imagine a bowl of spaghetti. If the noodles are just tangled together but not physically tied to one another, you can easily separate them or change the shape of the pile. This is very similar to how thermoplastic polymers behave.

Thermoplastics, like PVC (Polyvinyl Chloride) and Nylon-6, consist of long, linear or slightly branched chains. Because the intermolecular forces holding these chains together are relatively weak (like van der Waals forces or hydrogen bonds), heating them gives the chains enough kinetic energy to slide past one another. This allows thermoplastics to be melted, reshaped, and recycled multiple times without altering their chemical composition.

Now, imagine taking that same bowl of spaghetti and chemically welding the noodles together at various points. You have just created a three-dimensional, interconnected network. This is the structural reality of thermosetting polymers.

Thermosetting polymers are heavily branched or cross-linked molecules. The magic—and the permanence—happens during the molding process. When these polymers are heated in a mold, they undergo extensive chemical reactions that form strong covalent bonds (cross-links) between the adjacent polymer chains.

Once this cross-linking occurs, the polymer sets into an infusible and insoluble mass. If you try to heat it again, the strong covalent bonds will not break to allow the chains to slide. Instead, if heated to extreme temperatures, the polymer will simply degrade and char. Because of this, thermosetting plastics cannot be remelted, reshaped, or reused.

Let's evaluate the choices provided in the question:

1. PVC (Polyvinyl Chloride): This is a classic thermoplastic used in pipes and cables. It softens on heating. 2. Nylon-6: A synthetic fiber and a thermoplastic polyamide. It can be melted and spun into fibers. 3. Buna-N: This is a synthetic rubber, classified as an elastomer. While it has some cross-linking (vulcanization), it is primarily known for its elastic properties rather than being a rigid thermoset. 4. Bakelite: This is the star of the show. Bakelite is a phenol-formaldehyde resin. During its formation, it undergoes extensive cross-linking to form a rigid, 3D network.

Because of its excellent heat resistance and electrical insulating properties, Bakelite is widely used to make electrical switches, plug boards, and the handles of cooking utensils. It is the quintessential example of a thermosetting polymer. Therefore, Bakelite is the correct answer.