General Mechanism of Polymerization PDF

General mechanism of polymerization Presented By : Rawan Osama Abo-ElMakarem Nada Ahmed Mohamed  1 General mechanism polymerization consist of 3 main steps 1- initiation 2- propagation 3- termination Larana Universit...

General mechanism of polymerization Presented By : Rawan Osama Abo-ElMakarem Nada Ahmed Mohamed  1 General mechanism polymerization consist of 3 main steps 1- initiation 2- propagation 3- termination Larana University | 2024  1- initiation 2 1:The initiation of polymerization is the first step in the polymerization process where the reactive species (initiator) is introduced to the monomer to start the formation of polymer chains. This step is crucial as it sets the stage for the propagation of the polymer chain. There are various types of polymerization processes such as free radical, cationic, anionic This process include two steps: 1 activation of moneer, 2- activation of initiator  2-propagation 3 In this step, the reactive species reacts with a monomer molecule to form a new reactive species. This new reactive species then reacts with another monomer molecule, and the process continues, leading to the growth of the polymer chain. Chain Growth: The propagation process repeats itself, with each new monomer addition resulting in the elongation of the polymer chain. This continuous addition of monomers occurs rapidly and can result in long polymer  3- Termination 4 Termination in the mechanism of polymerization refers to the process by which growth of a polymer chain comes to an end. There are generally two main types of termination: 1. Combination: This occurs when two growing polymer chains with active sites (free radicals, ions) combine to form a single stable polymer chain 2. Disproportionation: This occurs when a hydrogen atom is transferred from one growing polymer chain to another, resulting in the formation of two stable polymer chains: one saturated and one unsaturated. Larana University | 2024  5 INITIATOR is a special chemical compound that starts the polymerization process. Think of it as the "spark" that lights the fire. This initiator molecule breaks down into highly reactive fragments under certain conditions (like heat or light). These reactive fragments are called free radicals, cations, or anions, and they are the ones that react with monomer molecules to start building the polymer chain.  6 IMPORTANCE OF INITIATORS Starting the Reaction: Initiators are responsible for starting the polymerization 1 process. They generate active sites, such as free radicals, cations, or anions, which are essential for the initiation of the reaction. Controlling the Rate of Polymerization: The type and concentration of initiators 2 used can significantly influence the rate of polymerization. A higher concentration of initiators generally leads to a faster reaction. Determining Polymer Properties: The choice of initiator can affect the molecular 3 weight, distribution, and overall properties of the polymer. Different initiators can lead to polymers with different characteristics.  7 EXAMPLES OF INITIATORS: Free radical Anionic Larana University | 2024 Example: Benzoyl Peroxide (C₆H₅CO₂)₂ Example: n-Butyllithium (n-BuLi) Role: Provides a carbanion that initiates Role: Decomposes to form the polymerization process. benzoyloxyl radicals which initiate the polymerization process. cationic Ring- opening Example: Boron Trifluoride (BF₃) Example: Tin(II) Octoate (Sn(Oct)₂) Role: Forms a complex with water Role: Used in the ring-opening (BF₃ H₂O) to produce a proton, which acts as polymerization of lactides to produce a cationic initiator. polylactic acid (PLA)  8 Free radical polymerization It is a type of polymerization where polymer chains are formed through chain reactions initiated by the formation of free radicals. A free radical is an atom or group of atoms that has an unpaired electron, making it highly reactive. Free radicals react with monomers to form new polymer chains.  6 IONIC POLYMERIZATION Cationic polymerization It is a specific type of ionic polymerization where a positive ion (cation) is used to initiate the reaction. The cation reacts with the monomer to form a carbocation, which in turn reacts with other monomers to grow the polymer chain Anionic polymerization is a type of chain-growth polymerization in which the active center of the polymer chain is a negatively charged ion (anion). This process is characterized by the initiation, propagation, and termination steps driven by anions. It is commonly used for the polymerization of monomers containing electron-withdrawing groups, such as styrene, butadiene, and acrylonitrile.  12 Ring-opening polymerization Ring-Opening Polymerization (ROP) is a type of polymerization in which the monomer units have a cyclic structure and the polymerization process involves opening of the ring to form a linear or branched polymer. Larana University | 2024 THANK YOU