Addition Polymerization vs Condensation Polymerization
Polymers are large molecules, which has the same structural unit repeating over and over. The repeating units are called monomers. These monomers are bonded to each other with covalent bonds to form a polymer. They have a high molecular weight and consist over 10,000 atoms. In the synthesis process, which is known as polymerization, longer polymer chains are obtained. There are two main types of polymers depending on their synthesis methods. If the monomers have double bonds between carbons, from addition reactions polymers can be synthesized. These polymers are known as addition polymers. In some of the polymerization reactions, when two monomers are joined, a small molecule like water is removed. Such polymers are condensation polymers. Polymers have very different physical and chemical properties than their monomers. Moreover, according to the number of repeating units in the polymer, properties differ. There are a large number of polymers present in the natural environment, and they play very important roles. Synthetic polymers are also used widely for different purposes. Polyethylene, polypropylene, PVC, nylon, and Bakelite are some of the synthetic polymers. When producing synthetic polymers, the process should be highly controlled to get the desired product always. Polymers are used as adhesives, lubricants, paints, films, fibers, plastic goods, etc.
What is Addition Polymerization?
The process of synthesizing addition polymers is known as addition polymerization. There should be multiple bonded monomers to initiate such reaction. This is a chain reaction; therefore, any number of monomers can join into a polymer. There are three steps to a chain reaction, they are initiation, propagation and termination. For an example, we will take the synthesis of polyethylene, which is an additional polymer used to make products like garbage bags, food wrap, jugs, etc. The monomer for polyethylene is ethene (CH2=CH2). Its repeating unit is –CH2-. In the initiation step, peroxide radical is generated. This radical attacks the monomer to activate it and produce a monomer radical. During the propagation phase, the chain grows. Activated monomer attacks another double bonded monomer and attaches together. Ultimately the reaction stops when two radicals join together and form a stable bond. Chemists can control the length of the polymer chain, reaction times and other factors to obtain the required polymer.
What is Condensation Polymerization?
Any condensation process, which results in the formation of polymers, is known as condensation polymerization. A small molecule like water or HCl is released as a by-product during the condensation polymerization. The monomer should have functional groups in ends, which can react together to continue the polymerization. For example, if the joining ends of two molecules have a –OH group and a –COOH group, a water molecule will be released and an ester bond formed. Polyester is an example for a condensation polymer like that. In the synthesis of polypeptides, nucleic acids or polysaccharides, condensation polymerization takes place within biological systems.
What is the difference between Addition Polymerization and Condensation Polymerization?
• Addition polymerization is the reaction between monomers with multiple bonds, where they join together to form saturated polymers. In condensation reactions, functional groups of two monomers react together releasing a small molecule to form a polymer.
• Saturated monomers are participating in condensation reaction whereas for the addition polymerization, monomer should be an unsaturated molecule.
• Addition polymers are non-biodegradable and hard to recycle compared to condensation polymers.
• Addition polymerization is a rapid process, and it produces high molecular weight polymers in contrast to condensation polymerization.