Use high-density poly(ethene) and low-density poly(ethene) as examples to explain the difference that branching can make to the properties of a polymer.

During the formation of poly(styrene), a volatile hydrocarbon such as pentane is often added. Describe how this affects the properties of the polymer and give one use for this product.

in HDPE there is little branching / in LDPE there is branching/side chains;

long chains can pack closely together/have greater forces of attraction so (HDPE) is more dense/more rigid/stronger;

side chains make (LDPE) more flexible/ideal for film products (such as food wrapping);

Accept opposite statements for marking points 2 and 3.

makes the polymer low density/good thermal insulator/expanded/softer/better shock absorber;

packaging/insulation;

Award [1 max] if thermal insulation given for both answers.

Most candidates had difficulty explaining the difference between HDPE and LDPE in terms of branching. Many mixed up the branching and properties, for example stating that increased branching led to a higher density.

Part (b), which required candidates to explain why pentane is added to poly(styrene) to improve its thermal insulation properties, was also difficult for most candidates.