Looking for classes? Ksquare Career Institute, Bengaluru →
The straight chain polymer is formed by
A
hydrolysis of $(CH_3)_2SiCl_2$ followed by condensation polymerization
B
hydrolysis of $(CH_3)_3SiCl$ followed by condensation polymerization
C
hydrolysis of $CH_3SiCl_3$ followed by condensation polymerization
D
hydrolysis of $(CH_3)_4Si$ by addition polymerization
Detailed Solution
Silicones are made by hydrolysis of alkyl-substituted chlorosilanes followed by condensation polymerisation; the number of Cl atoms decides how many Si–O–Si links each unit can form.
$(CH_3)_2SiCl_2$ has two Cl atoms: hydrolysis gives $(CH_3)_2Si(OH)_2$ with two –OH groups, which can condense at both ends to give a long straight chain: $n(CH_3)_2Si(OH)_2 \rightarrow -[Si(CH_3)_2-O]_n- + nH_2O$
$(CH_3)_3SiCl$ gives $(CH_3)_3SiOH$ with only one –OH group; it can only form a dimer and acts as a chain-terminating (end-blocking) unit.
$CH_3SiCl_3$ gives $CH_3Si(OH)_3$ with three –OH groups; it forms a cross-linked, three-dimensional polymer.
$(CH_3)_4Si$ has no Cl and cannot be hydrolysed.
Hence the straight chain polymer is formed from $(CH_3)_2SiCl_2$.
$(CH_3)_2SiCl_2$ has two Cl atoms: hydrolysis gives $(CH_3)_2Si(OH)_2$ with two –OH groups, which can condense at both ends to give a long straight chain: $n(CH_3)_2Si(OH)_2 \rightarrow -[Si(CH_3)_2-O]_n- + nH_2O$
$(CH_3)_3SiCl$ gives $(CH_3)_3SiOH$ with only one –OH group; it can only form a dimer and acts as a chain-terminating (end-blocking) unit.
$CH_3SiCl_3$ gives $CH_3Si(OH)_3$ with three –OH groups; it forms a cross-linked, three-dimensional polymer.
$(CH_3)_4Si$ has no Cl and cannot be hydrolysed.
Hence the straight chain polymer is formed from $(CH_3)_2SiCl_2$.