Graft and block copolymers are important classes of copolymers in which two or more chemically different monomer units are incorporated into the same polymer molecule. Although both contain distinct polymer segments and can combine the properties of different polymers, they differ mainly in the way these segments are arranged along the polymer backbone. This structural difference produces significant variations in their physical properties, morphology, synthesis, and applications. A block copolymer is a copolymer in which long sequences, or blocks, of one type of monomer are connected directly to long sequences of another type of monomer. In a simple diblock copolymer, represented as A–B, a polymer chain consists of one continuous block of monomer A followed by one continuous block of monomer B. Triblock copolymers may be represented as A–B–A or B–A–B, while more complicated structures can contain several blocks. Thus, the different polymeric segments occur sequentially along the main chain. For example, a block copolymer may be represented as A–A–A–A–B–B–B–B where A and B represent repeating units derived from two different monomers. The A units form one continuous block and the B units form another continuous block. Because the chemically different segments are joined end-to-end, block copolymers often exhibit properties associated with both constituent polymers. A graft copolymer, on the other hand, consists of a main polymer backbone made predominantly from one type of monomer, with branches or side chains made from another type of polymer attached to the backbone. It can be represented schematically as A–A–A–A–A–A | | B B | | B B Here,