This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Inhibition and Retardation”.
1. The substance that reduces the rate and degree of polymerization, without halting the propagation process, is called a___________
a) retarder
b) inhibitor
c) modifier
d) regulator
View Answer
Explanation: Inhibitors consume the radicals and completely suppress the polymerization and brings the rate of polymerization to a zero value.
2. Which of the following has the highest practical utility as an inhibitor?
a) benzoquinone
b) t-butyl catechol
c) nitro benzene
d) DPPH
View Answer
Explanation: DPPH (diphenylpicrylhydrazyl) is too stable toact as free radical but it has great potential to react with chain radicals to completely terminate them.
3. What is the order of inhibitor consumption in an inhibition process?
a) first
b) second
c) zero
d) none of the mentioned
View Answer
Explanation: In an ideal inhibition process, the consumption rate is independent of inhibitor concentration and depends on the rate of generation of radicals, by any means. The radical generation is however independent of the inhibitor, thus the inhibitor consumption is of zero order.
4. The inhibition period is proportional to the monomer concentration in the system. State true or false.
a) true
b) false
View Answer
Explanation: The inhibition period does not depend on monomer concentration; instead, it is proportional to the initial concentration of the inhibitor.
5. What does the stoichiometric ratio and nature of products formed depends on, when the reaction of inhibitor radicals and chain radicals leads to copolymerization?
a) nature of monomer
b) initiator
c) solvent
d) all of the mentioned
View Answer
Explanation: The nature of non-radical products formed through reaction of inhibitor radicals and chain radicals, which may even lead to copolymerization, and the stoichiometric ratio, may not follow a uniform pattern which largely depends on the nature of monomer and overall polymerization environment including initiator, solvents, etc.
6. Where has the role of aromatic nitro compounds as an inhibitor or retarder been unsuccessful?
a) styrene polymerization
b) vinyl acetate polymerization
c) acrylate polymerization
d) vinyl chloride polymerization
View Answer
Explanation: These compounds have been unsuccessful or ineffective in any of retardation and inhibition, for acrylate polymerization.
7. What happens to the rate of polymerization at the end of inhibition period as compared to the rate for uninhibited monomer, when oxygen is used as an inhibitor?
a) recedes
b) exceeds
c) remains same
d) none of the mentioned
View Answer
Explanation: The rate of polymerization usually observed at the end of inhibition period due to oxygen often exceeds that for the uninhibited monomer under otherwise comparable conditions.
8. What is the necessary condition for hydroquinone to be used as inhibitors?
a) presence of α-hydrogen
b) presence of oxygen
c) presence of ring
d) none of the mentioned
View Answer
Explanation: The inhibitory action of hydroquinone is noticeable only in the presence of oxygen, as it become effective due to its oxidation to quinones.
9. What role does nitrobenzene play for the polymerization of methyl acrylate?
a) inhibitor
b) retarder
c) chain transfer agent
d) none of the mentioned
View Answer
Explanation: The value of inhibitor constants for a particular substrate widely depends on the reactivity of chain radicals. Nitrobenzene acts as a strong chain transfer agent for polymerization of methyl acrylate due to the less reactivity of methyl acrylate radicals.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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