Glass Transition

Glass Transition - The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. NOTE - The glass transition generally occurs over a relatively narrow temperature region and is similar to the solidification of a liquid to a glassy state: it is not a phase transition. Not only do hardness and brittleness undergo rapid changes in this temperature region but other properties, such as thermal expansion and specific heat also change rapidly. This phenomenon has been called second order transition, rubber transition and rubbery transition. The word transformation has also been used instead of transition. Where more than one amorphous transition occurs in a polymer, the one associated with segmental motions of the polymer backbone chain or accompanied by the largest change in properties is usually considered to be the glass transition.