The synthesis of polyethylene from ethylene monomer typically involves a process called polymerization. There are two main types of polymerization reactions used to synthesize polyethylene: free radical polymerization and coordination Ziegler-Natta polymerization. Both methods have different reaction mechanisms, which can affect the properties of the resulting polymer.1. Free Radical Polymerization:In free radical polymerization, the reaction is initiated by a free radical, which is a highly reactive species with an unpaired electron. The mechanism involves the following steps:a. Initiation: A free radical initiator, such as a peroxide or an azo compound, decomposes to generate free radicals. These radicals react with ethylene monomers, forming a new radical species.b. Propagation: The newly formed radical reacts with another ethylene monomer, creating a longer chain radical. This process continues, with the chain growing one monomer at a time.c. Termination: The reaction terminates when two radicals combine, forming a stable covalent bond, or when a radical reacts with an inhibitor or impurity.The properties of polyethylene synthesized via free radical polymerization can be affected by the reaction conditions, such as temperature, pressure, and the choice of initiator. This method typically produces high-density polyethylene HDPE and low-density polyethylene LDPE with a broad molecular weight distribution and a highly branched structure.2. Coordination Ziegler-Natta Polymerization:Coordination polymerization, also known as Ziegler-Natta polymerization, uses a transition metal catalyst, typically titanium-based, and an aluminum-based co-catalyst. The mechanism involves the following steps:a. Initiation: The ethylene monomer coordinates to the metal center of the catalyst, and the catalyst inserts the monomer into the metal-carbon bond.b. Propagation: The growing polymer chain remains attached to the metal center, and new ethylene monomers continue to coordinate and insert into the metal-carbon bond, extending the polymer chain.c. Termination: The polymer chain is terminated by a transfer of the metal center to a hydrogen atom, an alkyl group, or another monomer.Ziegler-Natta polymerization produces linear polyethylene with a more controlled molecular weight distribution and a more crystalline structure. This method is commonly used to synthesize high-density polyethylene HDPE and linear low-density polyethylene LLDPE , which have improved mechanical properties, such as tensile strength and impact resistance, compared to LDPE.In summary, the specific reaction mechanism involved in the synthesis of polyethylene from ethylene monomer affects the properties of the resulting polymer. Free radical polymerization leads to a more branched structure with a broader molecular weight distribution, while coordination Ziegler-Natta polymerization results in a more linear and crystalline structure with a controlled molecular weight distribution. These differences in structure and molecular weight distribution influence the mechanical properties and applications of the resulting polyethylene.