A unique kind of polymer called a block copolymer is one in which each molecule is made up of two or more segments of a simple polymer (a block) linked together in some way. Copolymers, in which each molecule is formed of more than one type of monomer, and homopolymers, in which each molecule is composed of the same type of monomer, are the two categories into which polymers can be further subdivided. Copolymers are separated into block and random forms. The various monomers are arranged into discrete blocks in block copolymers. Depending on how many blocks each molecule includes and how they are organized, block copolymers can also be divided into other subcategories. Diblocks, triblocks, and multiblocks are the names given to block copolymers that contain two, three, or more blocks.
Some arrangements are star-shaped, where all of the blocks are connected by one of their ends at a single junction, and linear arrangements, where the blocks are connected end to end. Naturally, more intricate combinations are feasible. In a block copolymer, the number of monomer types may be less than or equal to the number of blocks. As a result, an ABC linear triblock has three different types of monomers, while an ABA linear triblock only has two.
