Question

Hydrolysis of dimethyldichlorosilane followed by condensation polymerization gives:

• A. Monomers
• B. Dimers
• C. Polymers
• D. Trimers

Answer 1

The correct option is C Polymers

The silane derivatives on hydrolysis give hydroxides which immediately condense by intramolecular elimination of water, resulting in a polymer chain.
$(C{H}_3{)}_{2}SiC{l}_2+2H_{2}O\to (C{H}_3{)}_{2}Si(OH{)}_2$
THEORY
Silicones:

• Synthetic organosilicon compounds having repeated $R_{2}SiO$ units held by Si – O – Si linkages.
• $(R_{2}SiO{)}_n$ where R = alkyl or aryl group.
• Silicones can be prepared from the following types of compounds only

1. $R_{3}SiCl$
2. $R_{2}SiC{l}_2$
3. $RSiC{l}_3$

• Formed by the hydrolysis of alkyl or aryl substituted chlorosilanes and their subsequent polymerisation.
• $C{H}_{3}Cl$ reacts with Si in the presence of Cu as a catalyst at a 573K various types of methyl-substituted chlorosilane of formula formed.

1. $MeSiC{l}_3$
2. $M{e}_{2}SiC{l}_2$
3. $M{e}_{3}SiCl$
4. small amount of $M{e}_{4}Si$

$MeCl+Si\underset{300{}^{\circ }C}{\overset{Cu}{\to }}MeSiC{l}_3+M{e}_{2}SiC{l}_2+M{e}_{3}SiCl+\text{traces of}M{e}_{4}Si$
Preparation:

• Hydrolysis of $(C{H}_3{)}_{2}SiC{l}_2$ followed by condensation polymerization yields straight chain polymers.

$2C{H}_{3}Cl+Si\underset{570K}{\overset{\text{Cu powder}}{\to }}\left(C{H}_3{)}_{2}SiC{l}_2\underset{-2HCl}{\overset{+2H_{2}O}{\to }}\right(C{H}_3{)}_{2}Si(OH{)}_2$

The chain length of the polymer can be controlled by adding $(C{H}_3{)}_{3}SiCl$ which blocks the ends.