This set of Polymer Engineering Question Bank focuses on “Living Polymers”.
1. What color of the medium is obtained when styrene is added to the naphthalene anion for initiation of polymerization?
Explanation: On addition of styrene monomer to the solution containing naphthalene radical, the medium gains an orange color due to the formation of orange colored styryl radical anions by transfer of an electron to the styrene monomer from the naphthalene anion radical.
2. The polymerization of methacrylonitrile using lithium metal in liquid ammonia takes place at a much faster rate than the lithium amide (LiNH2) in liquid ammonia. State true or false.
Explanation: The polymerization of methacrylonitrile using lithium metal in liquid ammonia takes place at a much faster rate than the corresponding amide (LiNH2) in liquid ammonia. This is because, metallic lithium initiates through the agency of solvated electrons formed in ammonia solution.
Li + NH3 → Li+(NH3) + e–(NH3).
3. What is the color of the metallic lithium in liquid ammonia solution?
b) light green
c) deep blue
Explanation: The deep blue color of the solution is due to the presence of solvated electrons.
4. What is the average degree of polymerization when styrene in polymerized using sodium naphthalene? (v is the average kinetic chain length)
Explanation: The average degree of polymerization is 2v in case of polymerization of styrene using sodium naphthalene, because the radicals form di-anions and propagates the chain at both ends.
5. Which of the following anionic initiators give the slowest polymerization rate in a non-polar medium?
a) sodium naphthalene
b) butyl lithium
c) metallic lithium in NH3
d) none of the mentioned
Explanation: In non-polar media, the initiator BuLi associates to degree of about 6 and the propagating species also associate. This results in the slow polymerization rate and longer time for complete conversion as compared to other anionic initiators.
6. How is the molecular weight distributed in the living polymers?
c) may be uniform or non-uniform
d) cannot be said
Explanation: The non-termination of polymers lead to the production of mono-disperse polymers which have uniform molecular weight distribution.
7. What is the utilization of living polymerization?
a) synthesis of block polymers
b) synthesis of functional-ended polymers
c) monodisperse polymers
d) all of the mentioned
Explanation: Living polymerization enables the formation of block polymers by adding a fresh monomer to the reaction. It results in the production of mono-disperse polymers and can also help in generating the functional –ended polymers by reacting the living ends with different reagents.
8. What is the application of star-shaped polystyrene produced by living polymerization with trifunctional initiator?
b) rheology control
d) dispersing agent
Explanation: The Star –shaped polystyrene polymer is used for the rheology control and are also used as strengthening agents.
9. Which of the following end group is formed when polystyrene is made to react with ethylene oxide?
a) carboxylic group
b) hydroxyl group
c) amine group
d) no end group
Explanation: Hydroxyl end groups are obtained on the reaction of polystyrene with ethylene oxide.
10. What are the functions of the bifunctional hydroxyl ended polymer formed by living polymerization technique?
a) cross-linking agents
b) elastomer synthesis
c) chain extension
d) all of the mentioned
Explanation: The bifunctional hydroxyl ended group polymer helps in elastomer synthesis and chain extension and also used as cross-linking agents.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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