Chemistry Reference
In-Depth Information
CHAPTER 1
Introduction
1.1 BACKGROUND
Polysiloxanes are unique among inorganic and semi-inorganic polymers;
they are also the most studied and the most important with regard to
commercial applications. Thus, it's not surprising that there is an exten-
sive literature describing the synthesis, properties, and applications of
these materials, including topics,
1-10
proceedings topics,
11-14
sections of
topics or encyclopedias,
15-58
review articles,
59-64
and historical articles.
65-74
The purpose of this volume is not to give a comprehensive overview of
these polymers but rather to focus on some novel and interesting aspects
of polysiloxane science and engineering, including properties, work in
progress, and important unsolved problems.
The Si-O backbone endows polysiloxanes with a variety of intriguing
properties. The strength of the Si-O bond, for example, imparts consider-
able thermal stability, which is important for high-temperature applica-
tions (e.g., as heat-transfer agents and high-performance elastomers). The
nature of the bonding and the chemical characteristics of typical side
groups impart low surface free energy and therefore desirable surface
properties. Polysiloxanes, for example, are used as mold-release agents,
waterproofing sprays, and biomedical materials.
Structural features of the chains give rise to physical properties that
are also of considerable scientific interest. For example, the substituted Si
atom and the unsubstituted O atom differ greatly in size, giving the chain
a nonuniform cross section. This characteristic affects the way the chains
pack in the bulk, amorphous state, which explains the unusual equation-
of-state properties (such as compressibility). Also, the bond angles around
the O atom are much larger than those around the Si, which makes the
