The chemical reaction mechanism involved in the polymerization of ethylene to produce polyethylene is called chain-growth polymerization or addition polymerization. This process involves the repeated addition of ethylene monomers to form a long polymer chain. There are several types of polymerization processes, but the most common ones are free radical polymerization, coordination polymerization Ziegler-Natta catalyst , and metallocene catalyst polymerization.1. Free Radical Polymerization: In this process, a free radical initiator e.g., peroxide or azo compound is used to generate a reactive free radical species. The free radical reacts with an ethylene monomer, forming a new radical that can react with another ethylene monomer. This process continues, leading to the formation of a long polyethylene chain.2. Coordination Polymerization Ziegler-Natta catalyst : This process uses a transition metal catalyst, typically titanium-based, along with an organoaluminum co-catalyst. The catalyst coordinates with the ethylene monomer, allowing it to insert into the metal-carbon bond, forming a longer chain. This process continues, leading to the formation of a long polyethylene chain with high molecular weight and controlled stereochemistry.3. Metallocene Catalyst Polymerization: This process uses a metallocene catalyst, which is a transition metal complex with cyclopentadienyl ligands. The catalyst coordinates with the ethylene monomer and inserts it into the metal-carbon bond, similar to the Ziegler-Natta catalyst. This process results in the formation of a long polyethylene chain with controlled molecular weight and stereochemistry.Factors that affect the length and properties of the resulting polymer chain include:1. Monomer concentration: Higher monomer concentration leads to a higher reaction rate and longer polymer chains.2. Temperature: Higher temperatures increase the reaction rate, but may also increase the rate of chain termination, leading to shorter polymer chains.3. Catalyst concentration and type: The type and concentration of the catalyst used can influence the polymer chain length, molecular weight distribution, and stereochemistry.4. Reaction time: Longer reaction times can lead to longer polymer chains, but may also result in increased chain termination and degradation.5. Chain transfer agents: The addition of chain transfer agents can control the molecular weight of the polymer by transferring the growing chain to another molecule, effectively terminating the chain and starting a new one.6. Polymerization process: The choice of polymerization process e.g., free radical, Ziegler-Natta, or metallocene can significantly impact the properties of the resulting polyethylene, such as molecular weight, molecular weight distribution, and stereochemistry.