Polyurethanes are the most well known polymers used to make foams. If you're sitting on a padded chair right now, the cushion is probably made of a polyurethane foam. But polyurethanes are more than just foam.
Polyurethanes are the single most versatile family of polymers there is. They are used for all kinds of things. Polyurethanes can be elastomers, and they can be paints. They can be fibers, and they can be adhesives. They just pop up everywhere. A very unusual polyurethane is spandex.
Of course, polyurethanes are called polyurethanes because in their backbones they have a urethane linkage.
In the 3-D model you can see the urethane groups. Look for the red oxygen and blue nitrogen atoms. Each of those blobs is a urethane.
The picture shows a simple polyurethane, but there are all kinds of ways to make polyurethanes, as long as they have a urethane linkage in the backbone. Some of them are very simple and some are more complex, like this one:
Polyurethanes can hydrogen bond very well, so they can be very crystalline. For this reason they are often used to make block copolymers with soft rubbery polymers. These block copolymers have properties of thermoplastic elastomers, which are polymers that can act like rubber or plastic.
One unusual polyurethane thermoplastic elastomer is spandex, which DuPont sells under the trade name Lycra®. What gives spandex its special properties is the fact that it has hard and soft blocks in its repeat structure. The hard blocks, which contain the urethanes, bond tightly to the urethanes in other chains to form fibers. While the hard sections are all clumped together the glycol sections of each chain stay soft and rubbery, allowing the whole chian to stretch. The result is a fiber that acts like an elastomer! So we use it to make exercise clothing like biker pants and swimsuits.
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