Polymerization is a chemical reaction in which monomers join together to produce long polymer chains or three-dimensional networks. Polymerization is usually accomplished by a variety of reaction pathways involving a variety of variables such as the functional groups of the reacting chemicals and their nonbonding interactions. Condensation polymerization and addition polymerization are the two most common types of polymerization.

What is Additional Polymerization?

Polymerization is a process in which monomers react to generate a polymer without forming by-products. In most circumstances, additional polymerizations are carried out in the presence of catalysts, which in some cases exercise control over structural elements that have a significant impact on the polymer’s properties. At least one double bond is required for addition polymerization, often known as chain reaction polymerization. Polymerization produces no by-products, nor does a molecule get lost during the process. The produced polymer has the same molecular weight as the sum of all monomers used in the polymerization. A chain reaction connects monomers by altering the bonds between them. 

Ring-opening polymerization

Ring-opening polymerization is an additive method that produces condensation-like polymers but follows the addition of polymerization stoichiometry. Polyethylene glycol, for example, is made by opening ethylene oxide rings:

HOCH₂CH₂OH + n C₂H₄O → HO(CH₂CH₂O)n + 1H

Nylon 6 (created to circumvent the patent on nylon 6,6) is made using additional polymerization, yet it has a chemical structure similar to other polyamides.

Examples of Additional Polymerization

(C3H6)n polypropylene can be made from (C3H6) propene, while ((C2H4)n) polythene can be made from (C2H4) ethene.

1. Homopolymers – A homopolymer is an additional polymer formed by the polymerization of a single polymeric component. Polythene (C2H4)n, for example.
2. Copolymers – A copolymer is the result of the addition polymerization of two distinct monomers, resulting in the development of additional polymers. For instance, Buna-N, Buna-S, and so on.

Other Addition Polymers

• PVC (Polyvinyl)- Vinyl chloride (H2C=CHCl) is used to make PVC (polyvinyl chloride), which is used to make a plastic wrap, simulated leather, water pipes, and garden hoses. The reaction is depicted in the diagram to the left.
• Polypropylene- The reaction that produces polypropylene (H2C=CHCH3) is depicted in the graphic’s middle reaction. It’s worth noting that the polymer bonds are always formed through the double bond’s carbons. Carbon #3 has already formed saturated bonds and is unable to form new ones. There is a methyl group on every other carbon.
• Polystyrene- The reaction is the same for polystyrene, which has a benzene ring connected to every other carbon. PS (polystyrene) is a #6 recyclable plastic. A polystyrene molecule is formed by polymerizing styrene monomers. The squiggly lines show how the polystyrene molecule stretches longer at both ends. Expanded polystyrene, also known as Styrofoam, is made by blowing small gas bubbles into liquid polystyrene and allowing it to solidify.
• Polystyrene with DVB- By co-polymerization of polystyrene with p-divinylbenzene, cross-linking between polymer chains can be introduced (DVB). Each vinyl group (-CH=CH2) on DVB’s molecule can be polymerized into a polymer chain much like any other vinyl group on a styrene monomer.

Characteristics of Addition Polymerization

• Additional Polymerization monomers only connect at the chain’s active site.
• There are three distinct steps to this process. Initiation, propagation, and finally termination are all steps in the process.
• Homo-chain polymers result from additional polymerization.
• The most essential feature is that there is no atom loss in addition to polymers.
• Lewis acids and radical initiators, in addition to polymerization, are catalysts.

Three Steps in Addition Polymerization

1. Chain Initiation- The polymerization process is usually started with the use of an initiator. A radical (free radical polymerization), a cation (cationic polymerization), an anion (anionic polymerization), or an organometallic complex can be used as the reactive starting molecule (coordination polymerization).
2. Chain propagation- Each new monomer unit adds to the chain, creating an active site for the next attachment.
3. Chain Termination- The radical, cation, or anion is “neutralized,” putting an end to the chain’s propagation.

Conclusion

At least one double bond is required for addition polymerization, often known as chain reaction polymerization. In addition, no molecule is lost during polymerization, and no by-product is produced. A polymer is created when all monomers used for polymerization have the same molecular weight. A chain reaction connects monomers by altering the bonds between them.