A5.7 Polystyrene and Styrofoam*
Styrene’s systematic name is phenylethene.
Figure 5.4 Styrene structure
It has a benzene ring attached to an ethene molecule.
Since it still has a double
$\textsf{C=C}$
bond, it can form an additional polymer, exactly like ethene ethane.
It is a thermoplastic.
It forms a transparent, clear plastic used for CD cases, rulers etc.
During its manufacture, a volatile hydrocarbon (like pentane) is introduced into the hot liquid polymer and droplets of the solution are then heated in steam – the pentane evaporates, and causes the polystyrene to form a foam – expanded polystyrene often simply known by its trade Styrofoam. This material can be formed into sheets, cups etc. and has excellent thermal insulating properties.

## 2-METHYLPROPENE

Figure 5.5 2-methylopropene and poly-2-methylpropene
This monomer cannot form atactic and isotactic polymers as the two
$\textsf{CH}_\textsf3$
groups will always be on opposite sides of the chain.
Structurally, this polymer resembles polypropene, but it has two methyl groups that are substituted on every other carbon atom of the chain.
Normally the polymer that forms will have two
$\textsf{CH}_\textsf3$
groups on every other carbon atom of the chain. However, it is possible for a monomer unit to add onto the chain in the opposite orientation; this gives rise to positions on the chain where there are two
$\textsf{CH}_\textsf3$
groups on adjacent carbon atoms of the main chain.
Poly-2-methylpropene is used in the manufacture of “butyl rubber” (first produced in 1931)