Chemistry Reference
In-Depth Information
CHAPTER 2
Preparation, Analysis, and Degradation
2.1 PREPARATION OF MONOMERS
Elemental silicon on which the entire technology is based is typically
obtained by reduction of the mineral silica with carbon at high
temperatures
1-3
:
(2.1)
SiO +2C i+2CO
2
→
The silicon is then converted directly to tetrachlorosilane by the reaction
(2.2)
Si +2Cl
→
SiCl
2
4
Tetrachlorosilane can be used to form an organosilane by the Grignard
reaction
(2.3)
SiCl +2RMgXRSiCl +2MgClX
4
→
2
2
This relatively complicated reaction has been replaced by the so-called
Direct Process or Rochow Process,
2,
4
which starts from elemental silicon
as is illustrated by the reaction
Si +2RCl RSiCl
2
→
(2.4)
2
This process also yields RSiCl
3
and R
3
SiCl, which can be removed by dis-
tillation. Compounds of formula R
2
SiCl
2
are extremely important as
intermediates to a variety of substances having both organic and inor-
ganic character.
5-8
Hydrolysis gives dihydroxy structures, which can
condense to give the basic [-SiR
2
O-] repeat unit. The nature of the
product obtained depends greatly on the reaction conditions.
8
Basic
catalysts and higher temperatures favor higher molecular weight linear
