Hideki Shirakawa pioneered the field of conductive polymers, overturning the common view that plastics do not conduct electricity. His demonstration that thin films of polyacetylene — an organic polymer — can become conductive when doped with small amounts of other chemicals earned him a share of the 2000 Nobel Prize in Chemistry (with Alan MacDiarmid and Alan Heeger). He was the second Japanese chemist to receive this award, after Kenichi Fukui in 1981. Shirakawa has died aged 90.

Shirakawa was born in Tokyo. After graduating from secondary school in Takayama City, he studied chemical engineering at the Tokyo Institute of Technology (now the Institute of Science Tokyo). He went on to pursue master’s and doctoral studies there, under the supervision of polymer chemist Shu Kambara, earning a Doctor of Engineering degree for his research on how blocks of organic molecules combine to form polymer chains.

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After completing his doctorate in 1966, Shirakawa was hired as a research associate in the laboratory of Sakuji Ikeda at Tokyo Tech. There, he began studying how acetylene molecules join together to form a polymer, using Ziegler–Natta catalysts (which are based on organic molecules containing transition metals).

In 1967, Shirakawa was joined in his experiments by a visiting researcher from South Korea, Hyung Chick Pyun. The pair were polymerizing acetylene using a catalyst composed of tetrabutoxytitanium and triethylaluminium to produce powdered polyacetylene.

On one occasion, however, the protocol failed to produce the powder. Instead, a ragged film formed on the surface of the solution in the flask. On closer inspection, it became clear that the visiting researcher had mistakenly used a much higher concentration of the catalyst than was intended — 1,000 times higher. Shirakawa went on to synthesize a thin film of polyacetylene with a metallic lustre by introducing acetylene gas into a flask coated on the inside with the concentrated catalyst.

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Subsequently, he travelled to the University of Pennsylvania in Philadelphia, where he worked with MacDiarmid and Heeger. The team discovered that adding small amounts of molecules that accept electrons (such as bromine) or that donate electrons (such as arsenic pentafluoride) increased the electrical conductivity of the thin film by a factor of ten million. This work led to the trio’s Nobel award.