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Addition Polymerisation
Concepts tested here
- Identifying the repeating unit
All Questions
2005 AIPMT 1 question
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The monomer of the polymer :
$\sim CH_2-C(CH_3)_2-CH_2-\overset{\oplus}{C}(CH_3)_2$
is :-The chain is built of the repeating unit $-CH_2-C(CH_3)_2-$.
The growing end is a carbocation, which shows that the polymer is formed by cationic addition polymerisation.
Adding back a double bond between the two carbons of the repeating unit gives the monomer $CH_2=C(CH_3)_2$.
This monomer is 2-methylpropene (isobutylene), and the polymer is polyisobutylene.
In cationic polymerisation the carbocation $\sim CH_2-\overset{+}{C}(CH_3)_2$ adds to the $CH_2$ end of a new monomer, regenerating a tertiary carbocation each time.
So the monomer is $H_2C=C(CH_3)_2$.