Chemistry Reference
In-Depth Information
CHAPTER 4
Some Characterization Techniques
Useful for Polysiloxanes
4.1 GENERAL COMMENTS
The general approach used in choosing a polymer suitable for a particular
application is:
Polymerization
↔
Structure roperties pplication
↔
↔
For example, if one wants a polymer for fire-resistant fabrics, then a poly-
mer with good high-temperature properties is required, which implies ar-
omatic structures, which suggest condensation polymerizations. More
relevant here, however, would be that a polymer remains elastomeric at
low temperatures. This requirement evokes a polymer with high flexibility
(low glass transition temperature), which indicates use of the polymeriza-
tion techniques used with the polysiloxanes.
4.2 OPTICAL AND SPECTROSCOPIC TECHNIQUES
An example of a relevant optical property is the birefringence of a de-
formed polymer network.
1
This strain-induced birefringence can be used to
characterize segmental orientation, and both Gaussian and non-Gaussian
elasticity.
2-9
Infrared dichroism has also been helpful in this regard.
10,
11
In
the case of the crystallizable polysiloxane elastomers, orientation is of crit-
ical importance with regard to strain-induced crystallization and the tre-
mendous reinforcement it provides.
11
Segmental orientation has also been
