What is true regarding free radical polymerization of ethylene?

Options

A. Polymerization is invoked by either peroxide initiator or radiation
B. Polymerization is exothermic in nature
C. Molecular weight gain occur in propagation step of polymerization
D. All of these

Answer

To solve the question regarding the free radical polymerization of ethylene (also known as ethene), we can break down the process into several key steps. Here’s a step-by-step solution:

### Step 1: Understanding the Initiation Step
In free radical polymerization, the process begins with the initiation step. This involves the use of an initiator, commonly a peroxide, which decomposes to form free radicals. For example, benzyl peroxide (C6H5COO-COC6H5) can be used as an initiator. When it decomposes, it generates free radicals that can initiate the polymerization process.

**Hint:** Look for the role of initiators in starting the polymerization process.

### Step 2: Chain Initiation
The free radicals generated from the initiator react with ethylene (C2H4) molecules. The radical takes an electron from the ethylene molecule, forming a new radical. This new radical is now capable of reacting with more ethylene molecules, thus starting the chain reaction.

**Hint:** Remember that the formation of a new radical is crucial for the continuation of the polymerization.

### Step 3: Chain Propagation
Once the chain is initiated, the next step is chain propagation. The radical formed in the initiation step reacts with additional ethylene molecules, adding them to the growing polymer chain. This process continues, and the chain length increases with each addition of ethylene, leading to a higher molecular weight of the polymer.

**Hint:** Focus on how the chain grows during this step and the importance of ethylene in the process.

### Step 4: Chain Termination
Eventually, the polymerization process reaches a termination phase. This can occur through various mechanisms, such as two growing chains combining to form a stable product or a radical reacting with a molecule that stops the chain growth. At this point, the polymer (in this case, polyethylene) is formed.

**Hint:** Consider how the process concludes and what results from the termination of the chain.

### Conclusion
In summary, the free radical polymerization of ethylene involves:
1. **Initiation**: Using an initiator (like benzyl peroxide) to generate free radicals.
2. **Propagation**: The free radicals react with ethylene to form a growing polymer chain, increasing molecular weight.
3. **Termination**: The polymer chain eventually terminates, resulting in the formation of polyethylene.

### Final Answer
Based on the steps outlined, the true statements regarding free radical polymerization of ethylene are:
1. Polymerization is initiated by either peroxide, initiator, or radiation.
2. Polymerization is exothermic in nature.
3. Molecular weight gain occurs during the propagation step.

Thus, all statements (A, B, C) are correct, leading to the conclusion that option D is correct.