Looking for classes? Ksquare Career Institute, Bengaluru →
Monomer of 
is : -
is : -
A
2-methyl propene
B
Styrene
C
Propylene
D
Ethene
Detailed Solution
The repeating unit $-C(CH_3)_2-CH_2-$ has a carbon with two methyl groups next to a $CH_2$.
Opening the double bond of $CH_2=C(CH_3)_2$ gives exactly this unit: $n\,CH_2=C(CH_3)_2 \rightarrow [-CH_2-C(CH_3)_2-]_n$
$CH_2=C(CH_3)_2$ is 2-methylpropene (isobutylene). The polymer is polyisobutylene, used in butyl rubber.
Propylene would give $[-CH_2-CH(CH_3)-]_n$ with only one methyl per unit.
So the monomer is 2-methyl propene.
Opening the double bond of $CH_2=C(CH_3)_2$ gives exactly this unit: $n\,CH_2=C(CH_3)_2 \rightarrow [-CH_2-C(CH_3)_2-]_n$
$CH_2=C(CH_3)_2$ is 2-methylpropene (isobutylene). The polymer is polyisobutylene, used in butyl rubber.
Propylene would give $[-CH_2-CH(CH_3)-]_n$ with only one methyl per unit.
So the monomer is 2-methyl propene.