Difference Between Polymer and Macromolecule

Main Difference – Polymer vs Macromolecule

Polymers have a molecular structure consisting chiefly or entirely of a large number of similar units bonded together. These units are called repeating units. These repeating units represent the monomers from which the polymer is made. Most of the times a macromolecule is formed due to polymerization. Then they are called polymer molecules. But some macromolecules are formed due to the chemical bonding of more atoms together. The main difference between polymer and macromolecule is that polymers contain repeating units that represent the monomers whereas not all macromolecules have a monomer in their structure.

Key Areas Covered

1. What is a Polymer
     – Definition, Classification, General Properties
2. What is a Macromolecule
    – Definition, General Properties
3. What is the Difference Between Polymer and Macromolecule
    – Comparison of Key Differences

Key Terms: Atoms, Macromolecular Crowding, Macromolecules, Monomers, Polymerization, Polymers, Repeating Units, Tacticity

What is a Polymer

A polymer is a type of macromolecule that is composed of a large number of repeating units. These repeating units represent monomers from which the polymer is made. Monomers are small molecules. These monomers have either double bonds or at least two functional groups per molecule. Then they can undergo polymerization in order to form polymer material.

Since polymers are diverse, they can be categorized into several different groups depending on different parameters. The classification is given below.

Classification of Polymers

Based on the Structure:

• Linear polymers
• Branched polymers
• Network/crosslinked polymers

Based on the Molecular Forces:

• Thermoplastic polymers
• Thermosetting polymers
• Elastomers

Based on the Source:

• Natural polymers
• Synthetic polymers

Based on the Method of Polymerization:

• Addition polymers
• Condensation polymers

Polymers have different properties depending on the repeating units present in the polymer, microstructure of the polymer material, etc. Some polymers show plasticity, some show elasticity; some polymers are strong and rigid, some are soft and flexible. Likewise, polymers show a wide range of properties.

Figure 01: Covalent Organic Frameworks

 General Properties of Polymers

• Most polymers are resistant to chemicals.
• Most polymers act as electrical and thermal insulators.
• Generally, polymers have a high strength when compared to their light weight.
• Some polymers can be obtained from natural sources, but most of the polymers are synthesized from petroleum oil.

The tacticity of polymers is another important concept regarding polymers. Polymers can be isotactic, syndiotactic or atactic. This tacticity is determined depending on the position of the pendant groups present in the polymer chains. If the pendent groups are on the same side, they are isotactic polymers. If the groups are in an alternating pattern, then they are syndiotactic. But if the pendant groups are positioned in a random manner, they are atactic polymers.

What is a Macromolecule

A macromolecule is a very large molecule with a diameter ranging from 100 to 10 000 angstroms. A macromolecule is often formed due to polymerization. Then they are called polymer molecules. A macromolecule is typically composed of a very large number of atoms chemically bonded to each other. Therefore, these molecules comprise a high molecular weight.

Some examples of macromolecules include natural and synthetic polymers, proteins, polysaccharides, nucleic acids, etc. These macromolecules are formed from smaller units known as monomers.

• Polysaccharides are formed from monosaccharides
• Proteins are formed from amino acids
• Nucleic acids are formed from nucleotides

Figure 2: Structures of Macromolecules

IUPAC Definition of Macromolecule

The IUPAC definition for a macromolecule is as below:

“A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetitions of units derived, actually or conceptually, from molecules of low relative molecular mass.”

Most macromolecules are insoluble in water due to their high molecular weight. They tend to form colloids. The concentration of a macromolecule in a solution can affect the rate and equilibrium of reactions of macromolecules present in the same solution. This phenomenon is named as macromolecular crowding.

Macromolecular Crowding

Macromolecular crowding alters the properties of molecules in a solution when high concentrations of macromolecules. Such conditions can occur in living cells. These high concentrations of macromolecules occupy a large amount of the volume of the cell. This reduces the volume of solvent that is available for other macromolecules. Then it affects the rates and equilibrium of their reactions.

Difference Between Polymer and Macromolecule

Definition

Polymer: A polymer is a type of macromolecule that is composed of a large number of repeating units.

Macromolecule: A macromolecule is a very large molecule with a diameter ranging from 100 to 10 000 angstroms.

Repeating Units

Polymer: Polymers are composed of repeating units.

Macromolecule: Macromolecules may or may not be composed of repeating units.

Monomers

Polymer:  Polymers are made from monomers.

Macromolecule: Macromolecules may or may not be made from monomers.

Solubility

Polymer: Some polymers are soluble in organic solvents.

Macromolecule: Most macromolecules are highly insoluble in water and other similar solvents.

Polymerization

Polymer: Polymers are formed essentially from polymerization.

Macromolecule: Macromolecule may form in different ways.

Conclusion

Polymers are macromolecules, but not all macromolecules are polymers. The main difference between a polymer and a macromolecule is that polymers contain repeating units that represent monomers whereas not all macromolecules have a monomer in their structure.

References:

1. “Macromolecule.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 7 Feb. 2011, Available here.
2. “Macromolecular crowding.” Wikipedia, Wikimedia Foundation, 4 Dec. 2017, Available here.

Image Courtesy:

1. “Covalent Organic Frameworks (space-filling diagram)” (CC BY-SA 3.0) via Commons Wikimedia
2. “Structures of macromolecules” By Cjp24 – Own work (CC BY-SA 3.0) via Commons Wikimedia