Question

Statement 1: Polybutadiene is an example of step growth polymer.
Statement 2: Copolymerisation of butadiene and acrylonitrile gives Buna-N.
A.Statement 1 and statement 2 are true and statement 2 is the correct explanation of statement 1.
B.Statement 1 and statement 2 are true but statement 2 is not the correct explanation of statement 1.
C.Statement 1 is true and statement 2 is false.
D.Statement 1 is false and statement 2 is true.

Answer 1

Hint: Polymerisation is the formation of polymers from their respective monomers (monomer is the smallest repeating unit).
Chain growth polymerisation is the type of polymerisation that involves the addition of the same or different monomers on a large scale to form a polymer.
Step growth polymerisation is the type of polymerisation that involves the repetitive condensation reaction between two different monomers.

Complete step by step answer:
Polybutadiene is not an example of step growth polymerisation. It is an example of chain growth polymerisation. This type of polymerisation leads to an increase in chain length. Here, the molecules of the same monomer or two different monomers add together on a very large scale to form a polymer.
The polymerisation reaction is given as follows:
\[nC{H_2} = CH - CH = C{H_2}\xrightarrow{{Polymerisation}}{\left[ { - C{H_2} - CH - CH - C{H_2} - } \right]_n}\]
Buna-N is formed by the copolymerisation of butadiene and acrylonitrile. Copolymerisation is the polymerisation reaction in which a mixture of more than one monomer is polymerised to form a copolymer. It can be done by both chain growth polymerisation and step growth polymerisation.
\[
  nC{H_2} = CH - CH = C{H_2} + n{C_6}{H_5}C{H_2} = C{H_2}\xrightarrow{{Polymerisation}} \\
  \;{\left[ { - C{H_2} - CH = CH - C{H_2} - CH({C_6}{H_5}) - C{H_2} - } \right]_n} \\
\]
The correct answer is (D) Statement 1 is false and statement 2 is true.

Note:
Polybutadiene:
-It is formed by the most simple polymerisation process, i.e., by the addition polymerisation or chain growth polymerisation.
-Here, the same monomer unit 1, 3-butadiene is polymerised to give polybutadiene.
-It contains a very long chain of the monomers.
-The chain keeps on increasing with the addition of monomers.
-It does not wear easily, hence it is generally used in making tyres.
Buna-N:
-It is formed by the process of copolymerisation.
-Its monomer units are 1, 3-butadiene and styrene.
-It contains alternate units of both the monomers.
-It is quite tough and is generally used as a substitute for rubber.