At which temperature range would you expect a polymer to transition from a hard state to a more flexible state, indicating its glass transition temperature (Tg)?

The glass transition temperature (Tg) is the point where a polymer changes from a stiff, glassy state to a more rubbery, flexible state; it usually falls between about –50 °C and 150 °C depending on the polymer. Below Tg the chains are frozen in place, so the material feels hard and brittle. As the temperature rises above Tg, the chains gain enough thermal energy to move past one another, making the polymer softer and more flexible. For example, polycarbonate has a Tg around 150 °C, so it is rigid below that temperature but becomes noticeably pliable once the room temperature rises above that value.