Block Copolymer Definition (Chemistry)

Nitrile, a plastic commonly used in disposable gloves, is a block copolymer.
Nitrile, a plastic commonly used in disposable gloves, is a block copolymer. Douglas Sacha / Getty Images

A block copolymer is a copolymer formed when the two monomers cluster together and form 'blocks' of repeating units.

For example, a polymer made up of X and Y monomers joined together like:

-Y-Y-Y-Y-Y-X-X-X-X-X-Y-Y-Y-Y-Y-X-X-X-X-X-

is a block copolymer where -Y-Y-Y-Y-Y- and -X-X-X-X-X- groups are the blocks.

Block Copolymer Examples

The material used to make automobile tires is a block copolymer called SBS rubber (acrylonitrile butadiene styrene).

The blocks in SBS rubber are polystyrene and polybutadine (StyreneButatineStyrene). Nitrile and ethylene-vinyl acetate are also copolymers.