Why is polystyrene (PS) an electrical insulator

The reason behind why graphite is electrically conductive is as ancient as the age of the Queen: that, electrons inside the benzene ring are delocalised.


However, if one looks the repeating unit of polystyrene:


[![polystyrene](https://i.stack.imgur.com/OmDBW.png)](https://i.stack.imgur.com/OmDBW.png)


we see the familiar benzene (phenyl?) ring, which logically should also contain delocalised electrons. But as all things turn out to be disappointing; polystyrene is an insulator (both thermal and electrical), and a pretty good one at that.


Why is this the case?


