Page 516 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Testing and Spectrometric Characterization of Polymers 479

3. Surface properties are important to the physical and chemical behavior of polymers. Similar
to smaller molecules, polymer surface structures can be determined using a variety of tech-

niques, including Auger electron spectroscopy, near-field optical microscopy, electron micro-
copy, SPM, SIMS, and certain IR and MS procedures.
4. Thermal analysis measurements allow the measure of polymer behavior as a function of tem-
perature, time, and atmosphere. DSC/DTA measures changes in energy as temperature is
changed and allows the determination of many valuable parameters, including T and T .
g m
TGA measures weight changes as a function of temperature.
5. The electrical properties of materials is important for many of the higher technology appli-
cations. Measurements can be made using alternating and/or direct current. The electrical
properties are dependent on voltage and frequency. Important electrical properties include
dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole
moment, electrical resistance, power loss, dissipation factor, and electrical breakdown.
Electrical properties are related to polymer structure. Most organic polymers are nonconduc-
tors, but some are conductors.
6. Important physical properties of polymers include weatherability, chemical resistance, and
optical properties. Polymers generally show good to moderate chemical resistance when com-
pared to metals and nonpolymers.

GLOSSARY

ASTM: American Society for Testing and Materials.
BSI: British Standards Institution.
Chemical shifts: Peaks in NMR spectroscopy.
Dielectric constant: Ratio of the capacitance of a polymer to that in a vacuum.
Dielectric strength: Maximum applied voltage that a polymer can withstand without structure
change.
Differential scanning calorimetry (DSC): Measurement of the difference in changes in the
enthalpy of a heated polymer and a reference standard based on power input.
Differential thermal analysis (DTA, DT): Measurement of the difference in the temperature
of a polymer and a reference standard when heated.
Environmental stress cracking: Cracking of polymers.
Glass transition temperature: Temperature where the onset of local or segmental mobility
begins.
Heat deflection temperature: Temperature at which a simple loaded beam undergoes a defi nite

defl ection.
Index of refraction: Ratio of the velocity of light in a vacuum to that in a transparent material
or mixture.
Infrared spectroscopy (IR): Technique used for the characterization of polymers based on
their molecular vibration and vibration-rotation spectra.
ISO: International Standards Organization.
Loss factor: Power factor multiplied by the dielectric constant.
Moh’s scale: Hardness scale ranging from 1 for talc to 10 for diamond.
Nuclear magnetic resonance spectroscopy (NMR): Based on the absorption of magnetic
energy by nuclei that have an uneven number of protons or neutrons; this absorption is
dependent on the particular chemical structure and environment of the molecule.
Oxygen index (OI): Test for the minimum oxygen concentration in a mixture of oxygen and

nitrogen that will support a candle-like flame of a burning polymer.
Power factor: Electrical energy required to rotate the dipoles in a polymer while in an elec-
trostatic fi eld.

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