Let's take a look at one called polydimethylsiloxane. This chain is so flexible that it's a liquid at room temperature, and it's even used to thicken shampoos and conditioners. This polymer's backbone is just plain stiff. You can heat this thing to over 500 o C and it will still stay in the glassy state. In order to make a polymer that's at all processable we have to put some flexible groups in the backbone chain.
Ether groups work nicely.
Fish Hooks and Boat Anchors Pendant groups have a big effect on chain mobility. Even a small pendant group can act as a fish hook that will catch on any nearby molecule when the polymer chain tries to move like corkscrew. Pendant groups also catch on each other when chains try to slither by each other. One of the best pendant groups for getting a high T g is the big bulky adamantyl group. And adamantyl group is derived from a compound called adamantane.