Angewandte Chemie International Edition

Cover image for Vol. 56 Issue 28

Editor: Peter Gölitz, Deputy Editors: Neville Compton, Haymo Ross

Online ISSN: 1521-3773

Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, ChemistryOpen, ChemPhotoChem, ChemPlusChem, Zeitschrift für Chemie

For full article and contact information, see Angew. Chem. Int. Ed. 1999, 38 (19), 2917 - 2919

Button and Buttonhole in a Single Molecule

A new chemical could make the production
of versatile polyurethanes easier

Whether in upholstery, insulation, shoe-soles, varnishes, or even artificial heart valves, polyurethanes (PUR) are found in nearly all areas of life as incredibly versatile all-around plastics. However, some are surprised to find that the method of making polyurethanes has hardly changed since their discovery over 60 years ago, when they were still considered to be a "crazy idea." Just as in the early days, two chemically different components are mixed together to synthesize polyurethanes, and the plastics are actually formed in the moulds of the upholstery or shoe-sole manufacturers. Chemists E.W. Meijer, Ron M. Versteegen and Rint P. Sijbesma, at the University of Eindhoven, have now found a way to include both PUR-components in one and the same molecule; these building blocks can be used to easily construct types of polyurethane that could only be synthesized in a roundabout way before.

The basic building blocks of polyurethanes are molecules that contain one of two groups of atoms, which chemists call alcohol and isocyanate groups. In principle, these groups act as "button" and "buttonhole": the building blocks, which each have either two buttons or two buttonholes, automatically link together in a reactor to form long chains.

Clearly, it would be easier to include both "button and buttonhole" in the same molecule, so only a single type of building block would have to be produced. This already works in the synthesis of the related polyamides (Nylon, Perlon), which are constructed in a similar fashion - only starting from acids and amines. Until now, complicated tricks had to be used to get this to work for polyurethanes, because the crucial isocyanates could only be synthesized under conditions that are unfriendly to the alcohols, causing them to undergo other reactions. This is where the team from Eindhoven comes in: they found a chemical that builds up isocyanates in a very gentle way, under conditions that leave any alcohol groups in the molecule untouched. In this way, Meijer and his coworkers could actually produce polyurethanes that contain only one type of building block.

The physical characteristics of these [n]-polyurethanes are very promising. Whether they will also be accepted in industry, however, mainly depends on whether the simple building blocks can easily be produced in large quantities. At this time, several million tons of polyurethanes are produced every year worldwide.