The approximate midpoint of the temperature range over which the glass transition takes place.
1: the approximate midpoint of a temperature range over which glass transition takes place. Also see coefficient of thermal expansion. 2: the temperature at which an amorphous polymer changes from the glassy state to the rubbery state.
Glass transition temperature is the temperature at which an amorphous polymer is transformed, in a reversible way, from a viscous or rubbery condition to a hard and relatively brittle one.