2.3
Polymers
A polymer is a chain of small molecules, called monomers, that are held together by covalent bonds. Organisms can synthesize biological polymers, or scientists can synthesize polymers in the laboratory.
Natural polymers include DNA, the genetic material found in all living organisms, and proteins, polysaccharides, and lipids, the building blocks of life.
Plastics are some of the most common synthetic polymers and include nylon, polyethylene, and teflon.
The process of monomers linking to each other to form a larger molecule is known as polymerization. Monomers polymerize by two distinct reaction mechanisms, condensation and addition.
Condensation polymerization is when two monomers with a reactive hydrogen atom and hydroxyl group, respectively, link to each other, with the release of water as a by-product. Most natural polymers are formed through condensation reactions.
In addition polymerization, monomers with carbon-carbon double bonds are added to each other to form a polymer without the generation of any by-product through the release of atoms.
Polymers that are made up of the same type of monomers are known as homopolymers, and those made up of different types of monomers are known as heteropolymers. Cellulose, the most abundant natural polymer, is a homopolymer of glucose, whereas agarose, a polymer of marine origin, is a heteropolymer of galactose and 3,6-anhydro-L-galactopyranose.
Polymers have various structures depending on their type of monomers. Linear polymers are long chains of monomers. For example, cellulose is a linear polymer held together by beta 1,4-glycosidic bonds.
Branched polymers have chains splitting off of the main chain, such as amylopectin, a component of starch that branches out after 24 to 30 monomers through alpha 1,6-glycosidic bonds.
Crosslinked polymers have two or more chains held together at several points like a ladder, such as a synthetically constructed silicon ladder polymer, or form a complex network of interlinked chains—like the gel formed by pectins in jellies and jams.
The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the properties that they exhibit. Additionally, functional groups that may be present on a polymer further define their properties. The individual units of a polymer are held together by stable covalent bonds that occur through either addition or condensation polymerization.
Addition Polymerization
Additional polymerization occurs when the monomers that participate in the reaction have double bonds. This reaction requires the presence of an external molecule that has an unpaired valence electron to initiate the reaction. This unpaired electron is highly reactive and forms a bond with one of the double bonds in a monomer, which leads to the monomer having an unpaired valence electron. This unpaired valence electron then associates with another monomer with double bonds leading to a chain reaction where the molecule keeps adding other monomers with double bonds to it. This results in the formation of a chain of monomers, with the one added most recently having an unpaired valence electron. This addition reaction continues until two chains with unpaired electrons react with each other to form a bond. This eliminates any unpaired valence electrons, resulting in the termination of the reaction.
Condensation Polymerization
Condensation polymerization, also known as step-growth polymerization, requires a catalyst, such as an acid or an enzyme, and the monomers must have at least two reactive functional groups, such as amines or carboxylic acids. Functional groups on monomers react with each other to form linkages such as ester or amide linkages and are accompanied by the loss of a small molecule, such as water. Condensation polymerization is a slower reaction compared to addition polymerization and, in many cases, requires the presence of heat.
This text is adapted from Openstax, Chemistry 2e, Chapter 20.1: Hydrocarbons.
A polymer is a chain of small molecules, called monomers, that are held together by covalent bonds. Organisms can synthesize biological polymers, or scientists can synthesize polymers in the laboratory.
Natural polymers include DNA, the genetic material found in all living organisms, and proteins, polysaccharides, and lipids, the building blocks of life.
Plastics are some of the most common synthetic polymers and include nylon, polyethylene, and teflon.
The process of monomers linking to each other to form a larger molecule is known as polymerization. Monomers polymerize by two distinct reaction mechanisms, condensation and addition.
Condensation polymerization is when two monomers with a reactive hydrogen atom and hydroxyl group, respectively, link to each other, with the release of water as a by-product. Most natural polymers are formed through condensation reactions.
In addition polymerization, monomers with carbon-carbon double bonds are added to each other to form a polymer without the generation of any by-product through the release of atoms.
Polymers that are made up of the same type of monomers are known as homopolymers, and those made up of different types of monomers are known as heteropolymers. Cellulose, the most abundant natural polymer, is a homopolymer of glucose, whereas agarose, a polymer of marine origin, is a heteropolymer of galactose and 3,6-anhydro-L-galactopyranose.
Polymers have various structures depending on their type of monomers. Linear polymers are long chains of monomers. For example, cellulose is a linear polymer held together by beta 1,4-glycosidic bonds.
Branched polymers have chains splitting off of the main chain, such as amylopectin, a component of starch that branches out after 24 to 30 monomers through alpha 1,6-glycosidic bonds.
Crosslinked polymers have two or more chains held together at several points like a ladder, such as a synthetically constructed silicon ladder polymer, or form a complex network of interlinked chains—like the gel formed by pectins in jellies and jams.
- Polymer – A large molecule or macromolecule composed of many repeated subunits.
- Polymerization – The process of creating polymers from monomers.
- Addition Polymerization – A type of polymerization in which the monomers just add together.
- Condensation Polymerization – A polymerization process where molecules join together, losing small molecules as byproducts.
- Monomers – The basic unit that can join together to form a polymer.
- Define Polymer – Understand the basic structure and properties (e.g., Polymer)
- Contrast Addition Polymerization vs Condensation Polymerization – Highlight key differences (e.g., water release in condensation).
- Explore Examples – Describe natural and synthetic polymers (e.g., proteins, nylon).
- Explain Polymerization Process – Understand how monomers combine to form polymers.
- Apply in Context – Understand the practical applications of polymers in daily life and various industries.
- What is a polymer and how are they formed?
- What are the differences between Addition and Condensation Polymerization?
- How do practical applications of polymers affect our lives?
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