Page 501 - Carrahers_Polymer_Chemistry,_Eighth_Edition

464 Carraher’s Polymer Chemistry

Direction of applied force

Liquid-free chamber

Temperature-controlled bath

Flat-ended needle
penetrator

Sample

FIGURE 13.5 Vicat apparatus for determining softening points.

Penetrator Load Environmentally controlled
chamber

Sample

FIGURE 13.6 Deflection temperature test assembly.

Figure 13.6) within a specified environment. As in other ASTM, the experimental conditions are

specified including sample size.

13.6.3 GLASS TRANSITION TEMPERATURES
Qualitatively, the T corresponds to the onset of short-range (typically 1–5 chain atoms) coordinated
g
motion. Actually, many more (often 10–100) chain atoms may attain sufficient thermal energy suf-

ficient to move in a coordinated manner at T . The T (ASTM D-3418) is the temperature at which

g
g
there is an absorption or release of energy as the temperature is raised or lowered, respectively.
The T can be measured by any means that allows changes in the conformation of the chains to
g
be detected. Thus, most of the thermal techniques allow T to be determined. Also, most spectral
g
techniques also allow T to be determined as well as techniques that measure volume changes. DMS
g
is also used to measure chain changes by subjecting the sample to repeated small-amplitude stains

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