Fun Materials Chemistry

The nylon rope trick is a classic example of a simple polycondensation. Nylon 6-10 forms at the interface of the two monomer solutions which can be extracted by a stir rod, or in our case a power drill.

Most materials expand with applied heat to allow for the increased entropy from more rapid molecular vibrations. However, elastomers, like rubber bands, contract upon heating! As the long polymer chains wiggle more vigorously, they become more entangled with one another and actually take up less space than before.

In the image, the photograph on the left shows the rubberband before heating stretched by a weight. The image on the right is the same rubber band after heating. It can be seen that the rubber band contracts by close to half an inch!

Biodegradable plastics are important in limiting built-up waste from packaging and other disposable materials. These plastics are typically made of naturally occuring monomers, such as glucose to form a starch. Specifically, this thermoplastic starch is comprised of two polymers, amylopectin and amylose, which are branched and straight chains, respectively.

To make the resultant film more ductile, glycerin is added as a plasticizer. These glycerin molecules lodge between polymer chains to increase the free volume between chains. This prevents close packing which decreases the glass transition temperature, thus making the film more flexible.