A large number of simple molecules called monomers combine together to form a macromolecule called a polymer. Each polymer has a repeating structural unit. If the repeating structural unit is derived from one type of monomer molecules. The polymer is said to be a homopolymer and if it is derived from two or more different types of monomer molecules , the polymer is said to be a copolmer. Both homopolymers and copolymers may be formed either by addition or condensation reactions. Alkenes and dienes polymerize by addition (chain growth) mechanism involving carbocations , carbanions or free radical intermediates. Dienes (chloroprene, isoprene, etc.) polymerize by 1, 4-addition mechanism to give cis-or trans-polymers. Natural rubber is quite soft and tacky but these properties can be improved by a process called vulcanization.
In contrast , bifunctional monomer molecules undergo , condensation or step-growth polymerization. Polymers which can be heated and reshaped as many times as desired are called thermoplastics , (polythene, polystyrene, PVC, teflon, etc.) while those which can be heated only once to give a particular shape are called thermosetting polymers (bakelite, melmac, etc.).
Which of the following sets contains only thermoplastics ?

Options

A. Polythene, Bakelite, Nylon 6
B. Glyptal, Melmac, PAN
C. PVC, PMMA, Polystyrene
D. Polypropylene, urea-formaldehyde , Teflon

Answer

To determine which set contains only thermoplastics, we first need to understand the characteristics of thermoplastics and thermosetting polymers.

### Step-by-Step Solution:

1. **Define Thermoplastics and Thermosetting Polymers:**
- Thermoplastics are polymers that can be reshaped upon heating. They do not undergo any significant chemical change when heated and can be remolded multiple times.
- Thermosetting polymers, on the other hand, can only be shaped once. Upon heating, they undergo a chemical change that makes them rigid and unable to be reshaped.

2. **Identify Common Examples:**
- Common examples of thermoplastics include:
- Polyethylene (PE)
- Polyvinyl Chloride (PVC)
- Polystyrene (PS)
- Poly(methyl methacrylate) (PMMA)
- Common examples of thermosetting polymers include:
- Bakelite
- Melamine
- Epoxy resins

3. **Analyze the Given Sets:**
- We need to examine the options presented in the question to identify which set contains only thermoplastics.
- For example, if one of the sets includes Bakelite, it cannot be the correct answer since Bakelite is a thermosetting polymer.

4. **Select the Correct Set:**
- After analyzing the sets, we identify the one that exclusively lists thermoplastics without including any thermosetting polymers.

5. **Conclusion:**
- The correct set that contains only thermoplastics is the one that includes examples like polyethylene, PVC, and polystyrene, while excluding any thermosetting polymers like Bakelite.