Block Copolymers
“A special kind of copolymer is called a "block copolymer". Block copolymers are made up of blocks of different polymerized monomers. For example, PS-b-PMMA is short for polystyrene-b-poly(methyl methacrylate) and is usually made by first polymerizing styrene, and then subsequently polymerizing MMA from the reactive end of the polystyrene chains. This polymer is a "diblock copolymer" because it contains two different chemical blocks. You can also make triblocks, tetrablocks, multiblocks, etc. Diblock copolymers are made using living polymerization techniques, such as atom transfer free radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), ring-opening metathesis polymerization (ROMP), and living cationic or living anionic polymerizations. An emerging technique is chain shuttling polymerization. The most powerful strategy to prepare block copolymers is the chemoselective stepwise coupling between polymeric precursors and heterofunctional linking agents. This method enables access to peculiarly exotic structures such as tetrablock quarterpolymers ABCD.” (Wikipedia, Block Copolymers, 6/20/2011