MacDiarmid, Alan Graham (1927-), a New Zealand-born American chemist. He shared the 2000 Nobel Prize in chemistry with American physicist Alan Jay Heeger and Japanese chemist Hideki Shirakawa who discovered and developed plastic materials through which electric current can flow.

MacDiarmid was born in 1927 in Masterton, New Zealand. He received a Ph.D. degree in chemistry from the University of Wisconsin in 1953 and a Ph.D. degree in chemistry from Cambridge University in the United Kingdom in 1955. He joined the faculty of the University of Pennsylvania in 1955 and remained a professor of chemistry there.

MacDiarmid Heeger, and Shirakawa conducted their prize-winning research at the University of Pennsylvania, publishing their discovery in a scientific journal in 1977. They won the prize for their work on special polymers, the basic substances of which plastics are made. A polymer is a huge molecule formed by the joining of many smaller molecules into a long chain. The small building units are called monomers. A monomer, in turn, consists of two or more joined atoms. The atoms within a monomer are joined to each other by connections known as bonds. Bonds between atoms also join the monomers that make up a polymer.

There are several kinds of bonds. MacDiarmid and his colleagues developed conducting polymers by manipulating covalent bonds. A covalent bond consists of a pair of electrons that are shared by two atoms. An ordinary electric current is a flow of electrons. The manipulation of the bonds freed a small number of electrons from bonds so that these electrons could flow.

The idea of being able to combine the flexibility and low weight of plastics with the electric properties of metals spurred scientists worldwide to develop a number of products using conductive polymers. Applications include solar cells, which use sunlight to generate electric power, and displays in mobile telephones and television sets. Lightweight, rechargeable batteries made of these materials could replace polluting automobile engines with environmentally safe electric motors.