GK12 Research Based Lesson
Glass Transition
Objective: Introduce the concept of the glass transition to students in chemistry. Show what happens to
a polymer above and below the glass transition. Emphasize that the glass transition is a physical
transition.
Materials:
 Racquetballs
 Liquid nitrogen in metal dewar
 Tongs
 Styrofoam cup
 Polymer samples
 Acetone
 Ice
 Beakers
 Water
Demonstration: The racquetball is bouncy and rubbery at room temperature, but when submerged in
liquid nitrogen for a few minutes, it turns into a glass. Bouncing the racquetball produces a completely
different sound, as well as almost no energy return. This example demonstrates that the glass transition
is a physical transition. Just like melting and evaporation, turning a polymer into a glass is completely
reversible (although it takes time).
For good measure, and to make sure the kids are awake, the racquetball should be shattered by
throwing it into the ground while it is glassy.
Laboratory: I used three different thiol-alkene polymer samples with different glass transitions and
asked the students to try and find the glass transition by bending the samples. They had three different
temperatures: room temperature (about 21°C), an ice-water bath (0°C) and an ice-acetone bath (about 20°C). Since all three samples were rubbery at room temperature, the students had to find which
cooling bath reached the glass transition temperature for the polymers. Students were consistently able
to find the glass transition temperature for one of the samples.
Since the lesson was right at the beginning of the semester, the students were also asked to make as
many observations on the samples as they could, to get them used to the idea of recording
observations.