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Block, Random & Alternating Copolymers: Structure & Examples

Anne Kamiya, Danielle Reid
  • Author
    Anne Kamiya

    Anne has experience in science research and writing. She has a graduate degree in nutrition (gut microbiome & nutritional microbiology) and undergraduate degrees in microbiology (immunology & medical microbiology) and English (myth & folklore). She has also worked as an ocean & Earth science educator.

  • Instructor
    Danielle Reid

    Danielle has taught middle school science and has a doctorate degree in Environmental Health

Explore copolymers. Learn the definition of a copolymer and understand its properties. Discover the different types of copolymers with various examples. Updated: 05/15/2022

Table of Contents


What is a Copolymer?

Lego blocks are made from a plastic called acrylonitrile butadiene styrene, which is a polymer comprised of three different monomers: (1) acrylonitrile, (2) butadiene, and (3) styrene. In chemistry, a monomer is defined as a molecular subunit that bonds to numerous identical subunits to create a very large molecule called a polymer. Although Lego blocks are polymers, they are also classified as copolymers because their plastic is made from three kinds of monomers. What is a copolymer? Copolymer is the scientific term for a polymer created from two or more different monomer subunits. Because Lego blocks contain many acrylonitriles, butadiene, and styrene subunits, the plastic it is made from is a copolymer.

Copolymer definition can also be visualized with a Lego analogy. Imagine a bag filled with thousands of Lego pieces. Inside the bag are three types of blocks. Each block type represents a monomer, and any structure built from the three blocks is a copolymer.

A photograph of many blue Lego plates.

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  • 0:02 What Are Copolymers?
  • 1:57 Copolymer Structure
  • 2:57 General Properties
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Classification of Copolymers

The classification of copolymers includes multiple types based on how their monomers are put together. The type of copolymers one might encounter in chemistry includes block copolymers, random copolymers, and alternating copolymers.

Block Copolymers

A homopolymer is a polymer chain that has been created from many repeating subunits of only one kind of monomer. A real-world example of a homopolymer is polystyrene, made from many interlinked styrene molecules, and another name for the Styrofoam used in coffee cups.

When one monomer is repeatedly attached to multiple identical copies of itself, it creates a homopolymer.

An image of twenty red circles with the letter A attached to each other.

Block copolymer chains are formed when a minimum of two different homopolymers bind together with a covalent bond. Block copolymers can be built from two, three, or more different types of homopolymers that come together. Many block copolymers are also thermoplastics, which means when they are heated, they become soft and can be manipulated into different shapes.

Random Copolymers

Random copolymer chains are formed when a minimum of two different monomer subunits bind together in an unpredictable way. There is no specific or set order to how random copolymers bind together as it is without consistency. These kinds of copolymers are also sometimes referred to as statistical copolymers.

Alternating Copolymers

Alternating copolymer chains are formed when a minimum of two different monomer subunits bind together in an alternating and repetitive manner. For example, nylon 6,6 is an alternating copolymer made of repeating (adipic acid)-(hexamethylenediamine)-(adipic acid)-(hexamethylenediamine) monomers.

Copolymer Structure

Copolymer structures are more easily described using a Lego analogy where each unique Lego block type represents a unique monomer. Although many structures built from the Lego blocks could be classified as a copolymer, there are several specific and distinct ways to put the blocks together. The Lego equivalent of a block copolymer would be like stacking one structure from only 2x2 red Lego bricks (A) and stacking a second structure from only 2x4 blue Lego bricks (B) and then connecting the two separate structures, e.g., AAAAA-BBBBB.

When one homopolymer attaches to another homopolymer, it creates a block copolymer.

An image of ten red circles in a row with the letter A attached to ten blue circles in a row with the letter B.

The Lego equivalent of a random copolymer would be building a stacked Lego structure out of 2x2 red Lego bricks (A) and 2x4 blue Lego bricks (B), which are put together in any order, e.g., ABAAABB.

When one at least two monomers attach to each other in large numbers but in random order, it creates a random copolymer.

An image of red circles with the letter A attached to blue circles with the letter B in random order.

The Lego equivalent of an alternating copolymer would be building a stacked Lego structure out of 2x2 red Lego bricks (A) connected to 2x4 blue Lego bricks (B) in consistent alternating order, e.g., ABABABAB.

When one at least two monomers attach to each other in large numbers in a consistent alternating order, it creates an alternating copolymer.

An image of red circles with the letter A attached to blue circles with the letter B in alternating order.

Copolymer Properties

The physical properties of copolymers are largely influenced by molecular weight and chemical structure. Some specific factors that affect copolymer properties include the length of the copolymer chain, the presence of any branching chains (chains that stick out from the main structure like branches), and the presence of any cross-linkages between chains, and a crystalline (organized) or amorphous (disorganized) structure.

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Frequently Asked Questions

What is a copolymer used for?

Copolymers are used for making a variety of materials with industrial, pharmaceutical, and every day use. A few examples of the uses of copolymers include plastic pipes, insulation for electrical wiring, synthetic clothing, medical non-latex gloves, hard plastics, soft plastics, and rubber bands.

What is a copolymer in chemistry?

In chemistry, when a polymer is made from more than one type of monomer subunit, it is called a copolymer. Copolymers may be made from two, three, or even more subunits that come together in different formations, such as a random copolymer, an alternating copolymer, or a block copolymer.

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