ABdiblock

ABdiblock, or AB diblock copolymer, is a polymer in which two chemically distinct blocks, A and B, are covalently connected in a single linear sequence. The blocks are typically only partially miscible, so the molecule can exhibit microphase separation, forming distinct domains on the nanometer scale when the product of the Flory-Huggins interaction parameter and the degree of polymerization is large enough.

Structure and synthesis

An AB diblock consists of a first block A grown from one chain end and a second block B appended after completion of A. Synthesis is commonly performed by sequential living polymerization: first prepare a living homopolymer of block A, then extend with monomer B to form AB. Techniques include living anionic polymerization, atom transfer radical polymerization (ATRP), and reversible addition–fragmentation chain-transfer (RAFT) polymerization. Alternative routes involve coupling two living blocks or linking preformed homopolymers. The architecture can be tuned by adjusting block lengths, composition (f_A), and total molecular weight.

Self-assembly and morphologies

In bulk or thin films, AB diblocks undergo microphase separation, yielding ordered structures such as lamellae, cylinders, or spheres depending on f_A and the product χN. In selective solvents, AB diblocks can form micelles with one block solvophilic and the other forming the core, enabling applications in templating and drug delivery.

Applications and examples

AB diblocks are used as compatibilizers in polymer blends, in lithography and nanoscale patterning, and as components of membranes and nanostructured materials. Common examples include polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) and poly(ethylene oxide)-block-polystyrene (PEO-b-PS). Their tunable properties make them versatile for research and industrial applications.